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How Warm Was the Medieval Warm Period?
Abstract
A frequent conclusion based on study of individual records from the so-called Medieval Warm Period (1000-1300 A.D.) is that the present warmth of the 20 th century is not unusual and therefore cannot be taken as an indication of forced climate change from greenhouse gas emissions. This conclusion is not supported by published composites of Northern Hemisphere climate change, but the conclusions of such syntheses are often either ignored or challenged. In this paper, we revisit the controversy by incorporating additional time series not used in earlier hemispheric compilations. Another difference is that the present reconstruction uses records that are only 900–1000 years long, thereby, avoiding the potential problem of uncertainties introduced by using different numbers of records at different times. Despite clear evidence for Medieval warmth greater than present in some individual records, the new hemispheric composite supports the principal conclusion of earlier hemispheric reconstructions and, furthermore, indicates that maximum Medieval warmth was restricted to two-three 20–30 year intervals, with composite values during these times being only comparable to the mid-20 th century warm time interval. Failure to substantiate hemispheric warmth greater than the present consistently occurs in composites because there are significant offsets in timing of warmth in different regions; ignoring these offsets can lead to serious errors concerning inferences about the magnitude of Medieval warmth and its relevance to interpretation of late 20 th century warming.
... The Medieval Warm Period almost superimposes with the Reconquest of the Iberian Peninsula by the Christian armies, which in the Northern region initiated practically immediately after the invasion [51,52]. For some authors, the Medieval Warm Period can be framed between the years 800 to 1200 ACE, as is the case for Broecker (2001), while, for others, such as Crowley and Lowery (2000), the Medieval Warm Period is in between the years 1000 and 1300 ACE, but that does not seem to be a very relevant issue at all [53,54]. However, it is the occurrence of this period that justifies, for example, events, such as the colonization of Iceland and Greenland by the Scandinavians, as reported by Hughes and Diaz (1994), Kuijpers and Mikkelsen (2009), or Ogilvie and Jónsson (2001) [55][56][57]. ...
... The Medieval Warm Period almost superimposes with the Reconquest of the Iberian Peninsula by the Christian armies, which in the Northern region initiated practically immediately after the invasion [51,52]. For some authors, the Medieval Warm Period can be framed between the years 800 to 1200 ACE, as is the case for Broecker (2001), while, for others, such as Crowley and Lowery (2000), the Medieval Warm Period is in between the years 1000 and 1300 ACE, but that does not seem to be a very relevant issue at all [53,54]. However, it is the occurrence of this period that justifies, for example, events, such as the colonization of Iceland and Greenland by the Scandinavians, as reported by Hughes and Diaz (1994), Kuijpers and Mikkelsen (2009), or Ogilvie and Jónsson (2001) [55][56][57]. ...
Climate change is a global phenomenon that has become a focus of concern for society, mainly due to its impacts on daily lives. Despite being a global issue that affects the entire planet, these effects are not felt in the same way in all regions, so the analysis of processes from a regional or local perspective allows a better adaptation of populations to the new reality, as well as being used as a supporting tool for decision making when implementing mitigation measures. For the present analysis, a region in Northern Portugal was chosen, which is in the Mediterranean region, considered one of the hot spots for climate change. In this region of Entre Douro e Minho, more specifically in the municipality of Guimarães, the climate of the last centuries was reconstructed based on documentary information and recent data collected and modeled for the region under study. The results show a successive alternation of hot and dry periods with colder and wetter ones, where climate instability seems to be the dominant trend over the last thousand years. Currently, with the advent of a new period of climatic instability, which, unlike the periods verified previously, now have an anthropic origin, there is a tendency for a new period to occur, in which conditions will tend to be hotter and drier. Knowing this trend in advance allows informed decisions to be made to mitigate some problems that can be associated with these conditions, such as the increase in the risk of wildfires, the proliferation of invasive species, the decrease in agriculture and forests productivity, or even the occurrence of extreme weather events.
... Figure 9. The proxy temperature results of tree-ring analyses of Crowley and Lowery (2000), Briffa (2000), Jones et al. (1998), andMann et al. (1999). The grand maximums and minimums of 60-and 88-year oscillations have been marked (Ollila and Timonen, 2022). ...
Anthropogenic global warming (AGW) is the prevailing theory of the IPCC for global warming. Greenhouse (GH) gases are the major drivers, whereas albedo, aerosols, and clouds have had cooling effects, and natural drivers have an insignificant role (<0.8 %). According to Assessment Report 6 (AR6), these radiative forcings (RF) have been a total of 2.70 Wm-2 causing a temperature increase of 1.27 °C in 2019. Many research studies are showing significantly lower RF and climate sensitivity values for anthropogenic climate drivers. Research studies offering natural climate drivers as the partial or total solution for global warming have gradually emerged like solar radiation changes, cosmic forces, and multidecadal, century-and millennial-scale oscillations. The cloud effects are still a major concern in General Circulation Models (GCMs). The cloudiness changes have a major role in cosmic effects like magnifying the warming effect of the Total Solar Irradiation (TSI). The 60-and 88-year oscillations are the best-known oscillations, which are commonly known as AMO (Atlantic Multidecadal Oscillation) and the Gleissberg cycle explaining the ups and downs of the global temperature in the 1900s. Mechanisms of long-term climate oscillations are still under debate. There are also essential differences between carbon cycle models and GH effect magnitude specifications. The synthesis of these natural climate drivers together with anthropogenic drivers constitutes an alternative theory called Natural Anthropogenic Global Warming (NAGW), in which natural drivers have a major role in dominating the warming during the current warm period. These results mean that there is no climate crisis and a need for prompt CO2 reduction programs.
... Climatically warmer periods have existed before in human historical times, e.g., the so-called Medieval Warm Period-documented archaeologically, geologically, and historically (Crowley and Lowery 2000;Zalasiewicz et al. 2020)-which is considered a localized phenomenon (Neukom et al. 2019). It is well documented that the last 400,000 years have witnessed alternating glacial and interglacial periods known as Milankovitch cycles (Campisano 2012), the causes of which are attributed to a combination of astronomical phenomena and not to human activities. ...
The challenge of this century is without a doubt to counter global warming. Land management, agriculture, and forests are responsible for 23% of total greenhouse gases (GHGs). In developing countries, such as those in African territories, where economic capacities are sometimes small and socio-cultural and linguistic perceptions are different, this requires a transition that is just and respectful of local culture and language, while at the same time helping to create labor conditions that respect gender and minors. This article describes a socio-technical ecological transition in the cocoa chain production in Côte d’Ivoire, which is not only the world’s leading producer of cocoa beans (45%) but also one of the African countries most prone to deforestation. Linguistic and multicultural aspects come together in Côte d’Ivoire, where more than 70 local languages are spoken. Intelligent digital approaches, agroecological issues, new methods, and sociocultural questions are embedded in a context of collaboration and co-creation, a living lab approach, to ensures sharing and co-creation among NGOs, farmers, companies, and researchers. A framework of socio-technical transition is presented, and this research aims to not only achieve the goals of a just ecological transition and reduce carbon footprint and deforestations but also to create diverse labour conditions, gender respect and inclusion.
... The Himalayas are critically prone to climate change and therefore a unique area for investigating proxy archives to gain information on the hydrological, thermal and ecological variabilities of regional to global significance (Chinthala et al., 2022). The last millennium witnessed a comparatively cooler Little Ice Age (LIA) phase between 1500 and 1850 CE (Grove, 2001) that primarily impacted the hydroclimate of the northern Hemisphere (Crowley and Lowery, 2000). Speleothem records revealed that the Himalayan regions experienced higher winter precipitation during the LIA . ...
The Kashmir region in the western Himalayas is located in a transition zone between areas dominated by the South Asian Summer Monsoon (SASM) and the North Atlantic Oscillation (NAO). Currently being primarily influenced by westerly disturbances (WDs), the area is important to decipher teleconnections between these two important circulation systems for the assessment of past climate variability. We evaluated climate-growth relationships of Abies pindrow (Royle ex D. Don) and reconstructed April to June (AMJ) self-calibrated Palmer drought severity index (scPDSI) for the south Kashmir region during the period 1643e2016 CE. Our reconstructed scPDSI revealed a long wet phase during 1650e1816 CE, indicating the impact of the Little Ice Age (LIA) over the region, followed by prominent drier post-LIA episodes. The mid 18th century (1730e1760 CE) was the wettest period in the past four centuries, whereas the period 1817 to 1865 CE marked the driest phase. These phases are consistent with other precipitation reconstructions from the WD-dominated western and Trans-Himalayan regions, but inconsistant with summer precipitation reconstructions from the SASM-dominated Himalayan regions. A significant positive correlation between our scPDSI reconstruction and the North Atlantic Oscillation (NAO) for the wet phase of the LIA suggests that the NAO remained dominant in modulating the winter and spring precipitation at the study region. During the 19th and 20th centuries, scPDSI was either weakly or negatively correlated with the NAO index, indicating the influence of other atmospheric circulation systems in driving the spring/summer precipitation in the study area. This study, augmented with other moisture records, contributes to analyze the temporal and spatial extent of moisture variability in a regional perspective.
... Similar abnormal climatic conditions have been observed during previous centuries, for example the medieval warm period (MWP), where annual mean temperatures were similar to those of the end of the 20th century. However, natural factors can account for the MWP temperature changes, whereas only anthropogenic interventions can explain the current anomalous global warming [3]. ...
Simple Summary
Global warming has caused a significant extension of the duration and the mean temperatures of summers; this is a serious stressor for dairy cows that are particularly sensitive to the high temperatures. Under these conditions, the productivity and the fertility of the animals are seriously compromised leading to considerable financial losses to the farmers. A deep understanding of the prevailing mechanisms of the cow to withstand this serious stressor, is prerequisite for planning and implementation of heat stress mitigation programs. To this end, in this review we analyze the main hormonal and molecular alterations that take place during heat stress, and which directly or indirectly affect cow’s fertility.
Abstract
Global warming is a significant threat to the sustainability and profitability of the dairy sector, not only in tropical or subtropical regions but also in temperate zones where extreme summer temperatures have become a new and challenging reality. Prolonged exposure of dairy cows to high temperatures compromises animal welfare, increases morbidity, and suppresses fertility, resulting in devastating economic losses for farmers. To counteract the deleterious effects of heat stress, cattl e employ various adaptive thermoregulatory mechanisms including molecular, endocrine, physiological, and behavioral responses. These adaptations involve the immediate secretion of heat shock proteins and cortisol, followed by a complex network of disrupted secretion of metabolic and reproductive hormones such as prolactin, ghrelin, ovarian steroid, and pituitary gonadotrophins. While the strategic heat stress mitigation measures can restore milk production through modifications of the microclimate and nutritional interventions, the summer fertility records remain at low levels compared to those of the thermoneutral periods of the year. This is because sustainment of high fertility is a multifaceted process that requires appropriate energy balance, undisrupted mode of various hormones secretion to sustain the maturation and fertilizing competence of the oocyte, the normal development of the early embryo and unhampered maternal—embryo crosstalk. In this review, we summarize the major molecular and endocrine responses to elevated temperatures in dairy cows, as well as the impacts on maturing oocytes and early embryos, and discuss the consequences that heat stress brings about in dairy cattle fertility.
... Sıcak Ortaçağ Dönemi (Küçük Klimatik Optimum) içerisinde hızlı sıcaklık artışı antropojenik nedenlere bağlanmadan, güneş radyasyonunun ve atmosferik salınımların yaşanması sonucu sıcaklığın daha yüksek değerlerde ulaşması ile açıklanmaktadır (Perry & Hsu, 2000;Crowley & Lowery, 2000;Rigozo vd., 2001). İç Anadolu'da Nar Gölü'nde yapılan çalışmada δ 18 O değerleri 1.100 Kal GÖ'de yüksek salınım göstermesi nemli koşulların yaşandığını göstermektedir (Dean vd., 2015). ...
Yelten Sazlığı (Antalya-Korkuteli) ilçesinde yer almaktadır. Bu çalışma Anadolu’da dağlık alanlarda yapılan ilk paleovejetasyon çalışması niteliğinde olup son ~2100 yıllık paleovejetasyon ve paleoiklim yapısını belirlemeyi amaçlamaktadır. Bu kapsamda Yelten Sazlığı’ndan Livingstone sondaj aleti ile sediman karotu alınmış ve radyokarbon ile tarihlendirme analizi sonucuna göre taban yaşının 2.157 (Kal GÖ) olduğu bilgisine ulaşılmıştır. Sediman karotu üzerinde fosil polen analizleri yapılmış ve sonuçları, Tilia 2.0.41 programında diyagrama dönüştürülmüştür. Elde edilen diyagramda üç ana ve üç alt zon belirlenmiştir. Zonlar arasında odunsu/ağaç taksonlarının toplam oranı (AP; arboreal polen) %98 ile %85,1 arasında değişim göstermiştir. Fosil polen bulguları içerisinde Pinus sp., Juniperus sp., Quercus sp. önemli AP taksonlarıdır. Otsu taksonları temsil eden NAP (non-arboreal polen) içerisinde ise Asteraceae, Chenopodiaceae ve Lactuaceae önemli taksonlar olmuştur. Ayrıca karot üzerinde μ-XRF analizleri uygulanmış ve element oranları standardize edilmiştir. Standardizasyon işlemi tamamlanan μ-XRF verilerinin grafikleri çizilmiş ve paleoiklim değişimleri ortaya koyulmuştur. Analizler sonucunda bölgede dört farklı küresel iklim döneminin (Roma Sıcak İklim Dönemi, 1400 Soğuk İklim Dönemi, Ortaçağ Sıcak Dönemi ve Küçük Buzul Çağı) özellikleri ile benzerlikler tespit edilmiştir. Güneybatı Anadolu’da daha önce gerçekleştirilen araştırma sonuçları ile karşılaştırılarak Roma, Bizans İmparatorluğu, Selçuklu ve Osmanlı Devleti döneminde iklim koşulları, arazi kullanımı ve vejetasyon yapısının değişimine dair bilgiler elde edilmiştir.
... EBSP showed Lineage A and Lineage B experienced rapid range expansions (Fig. 10A) during the Last Interglacial Period (LIG; Otto-Bliesner et al., 2006). Moreover, during the Medieval Warm Period (MWP; Crowley and Lowery, 2000), these lineages exhibited rapid expansions following a bottleneck event (Fig. 10B). Although these very recent events are not straightforward to explain without more comprehensive data and analyses, they fit into the general picture of a volatile population history expected for parasitic taxa, involving bottlenecks and expansions following host-switches as well as expansions due to post-glacial host range expansions. ...
Studies on parasite biogeography and host spectrum provide insights into the processes driving parasite diversification. Global geographical distribution and a multi-host spectrum make the tapeworm Ligula intestinalis a promising model for studying both the vicariant and ecological modes of speciation in parasites. To understand the relative importance of host association and biogeography in the evolutionary history of this tapeworm, we analysed mtDNA and reduced-represented genomic SNP data for a total of 139 specimens collected from 18 fish-host genera across a distribution range representing 21 countries. Our results strongly supported the existence of at least 10 evolutionary lineages and estimated the deepest divergence at approximately 4.99-5.05 Mya, which is much younger than the diversification of the fish host genera and orders. Historical biogeography analyses revealed that the ancestor of the parasite diversified following multiple vicariance events and was widespread throughout the Palearctic, Afrotropical, and Nearctic between the late Miocene and early Pliocene. Cyprinoids were inferred as the ancestral hosts for the parasite. Later, from the late Pliocene to Pleistocene, new lineages emerged following a series of biogeographic dispersal and host-switching events. Although only a few of the current Ligula lineages show narrow host-specificity (to a single host genus), almost no host genera, even those that live in sympatry, overlapped between different Ligula lineages. Our analyses uncovered the impact of historical distribution shifts on host switching and the evolution of host specificity without parallel host-parasite co-speciation. Historical biogeography reconstructions also found that the parasite colonized several areas (Afrotropical and Australasian) much earlier than was suggested by only recent faunistic data.
... CE; 55.5-50.5 cm). As already recorded in other peatlands across Europe (Lamentowicz et al., 2008(Lamentowicz et al., , 2009) and other natural archives (Esper et al., 2002;Tiljander et al., 2003), the dry phase may be explained by the Medieval Warm Period (WMP), which was characterized by temperatures comparable to the current ones (Bradley et al., 2003;Crowley and Lowery, 2000;Goosse et al., 2006). ...
In the last decades, climate and human activities significantly affected ecosystems, particularly in mountain areas. Whereas the Alps have been extensively studied for palaeoclimatic reconstructions, little information is available about ecological changes, especially in the Southeastern Alps. This study presents a palaeoclimatic and palaeoecological reconstruction from a 1500-years-old mountain peatland record: Wölflmoor, Bozen (Italy).
Through Physico-chemical proxies, testate amoeba, pollen, plant macro-fossils, and environmental DNA (eDNA) analyses, we pursued a twofold objective: 1) reconstructing the palaeoenvironmental variations of the peatland and the surrounding environment to identify the main dry/wet periods, and their correlations with climate and human activities; 2) testing the use of eDNA from a peatland in palaeoecological reconstructions. The dating highlighted a distinct change of age at a depth of 55.5–50.5 cm (ca. 800–930 calibrated years), which suggests a depositional gap (hiatus), at least in this section, occurred during the Medieval Warm Period, due to the increase in air temperature. However, the possible exploitation of the peatland by humans cannot be excluded. Indeed, the increase of Poaceae, Cerealia type, and Secale cereale, and the reduction of Fagus sylvatica and Quercus presented a high human pressure starting around 720 cal. CE. Environmental DNA metabarcoding results showed similar trends. However, it gave limitations such as the preferential amplification of the most abundant species, leading to a relatively small number of detected taxa. This is one of the first studies of eDNA metabarcoding from peatland; thus, we argue that ample room for improvement is expected in a short time, making eDNA metabarcoding a valuable complementary approach, primarily when both flora and fauna taxa are targeted.
... The late Holocene is essential in understanding the hydroclimatic conditions with emphasis on the climate anomalies of the last 2 millennia. Medieval Warm Period (MWP) and Little Ice Age (LIA) were observed in the Northern Hemisphere primarily impacting the European landmass and parts of the North Atlantic (Crowley and Lowery, 2000). Globally, the MWP is documented between 900 and 1300 C.E. (Graham et al., 2011) and the LIA is between 1500 and 1850 C.E. (Grove, 2001). ...
We reviewed the available climate records for the past 2 millennia based on the analyzed sediment and speleothem archives from different regions of South Asia. Speleothem records from the core-monsoon regions of the Indian sub-continent have revealed the Little Ice Age (LIA) as a climatically dry phase, whereas the same from the western and central Himalaya recorded LIA as wet. Moreover, the sediment-derived vegetation proxy records [pollen-spores and stable organic carbon isotope (δ¹³Corg)] from the western Himalaya also reported LIA as a dry phase. Heterogeneous results by different proxies during LIA enhanced our interest to understand the response of the proxies toward the primary precipitation sources, Indian summer monsoon (ISM) and winter westerly disturbances (WDs), over the Himalaya. We emphasize that in the Himalayan region, the vegetation predominantly responds to the ISM dynamics, whereas speleothem also captures the WD effect.
... CE; 55.5-50.5 cm). As already recorded in other peatlands across Europe (Lamentowicz et al., 2008(Lamentowicz et al., , 2009) and other natural archives (Esper et al., 2002;Tiljander et al., 2003), the dry phase may be explained by the Medieval Warm Period (WMP), which was characterized by temperatures comparable to the current ones (Bradley et al., 2003;Crowley and Lowery, 2000;Goosse et al., 2006). ...
... However, disagreement continues on the exact timing of both MCA and LIA intervals, which appear desynchronized worldwide (Crowley and Lowery, 2000;Broecker, 2001;Neukom et al., 2019), with many studies pointing to profound differences in temperature and precipitation gradients (e.g., Cronin et al., 2010;Jomelli et al., 2016). For example, while tropical East Africa experienced arid conditions during the MCA due to weak East African monsoons (Tierney et al., 2011), drier conditions associated with a positive phase of the North Atlantic Oscillation (NAO) characterizes the southern Levant during the same interval (Toker et al., 2012;Kushnir and Stein, 2019). ...
The climate of the Arabian Desert is not well documented during the past two millennia due to the scarcity of continuous and well-dated terrestrial archives in the region. Reliable interpretation from the climatic records from this region are pivotal for identifying periodicities of inter-annual to multi-decadal variability and trends driven by shifts in position of the Intertropical Convergence Zone (ITCZ) and the strength of the monsoons. A high-resolution multiproxy approach is presented for a ∼3.3 m composite core, GBW, from a karst lake located in Ghayl ba Wazir, southern Yemen. Sedimentary proxies, including particle size distribution, coupled with magnetic susceptibility (MS) and geochemistry (XRF), provide a comprehensive picture of sediment depositional changes that may be linked to climate and environmental variability over the southern Arabian Desert. The chronology of the GBW core is provided by five radiocarbon (¹⁴C) dates from terrestrial macrofossils (wood and twigs) extracted from sediment samples and indicates the core extends to ∼900 CE. Our data indicates generally wetter conditions from 930 to 1400 CE corresponding to the “Medieval climate anomaly (MCA)” followed by arid phases during 1,410–1700 CE coinciding with the “Little Ice Age (LIA)”. Evidence for a drier LIA include high authigenic calcium precipitation [Ca/(Al + Fe + Ti)], decreased TOC/TIC values, and gypsum precipitation, whereas the wetter MCA is characterized by higher detrital element ratios (Ti/Al, K/Al, Rb/Sr), and increased TOC/TIC and deposition of finer sediments (EM1). Furthermore, end-member mixing analyses (EMMA) derived from the grain-size distribution (EM2 and EM3) corroborates the deposition of coarser silt sediment through wind erosion and production of carbonate sand during the LIA concurrently with low lake levels under generally dry conditions. Aridity during the LIA is consistent with evidence and theory for weakened boreal summer monsoons during intervals of northern hemisphere cooling.
... The beginning of the millennium witnessed a relatively warm period in much of Europe. Known today as the Medieval Warm Period (or Medieval Climate Anomaly), this lasted from about 950 to 1250 CE (Crowley and Lowery, 2000;Mann et al., 2009). Subsequently, around 1400 CE, the continent was plunged into the Little Ice Age, a deep cold that lingered into the early 19th century CE (Mann et al., 2009) with some parts of the Northern Hemisphere experiencing as much as a 4°C drop in average temperatures in a few decades (D'Andrea et al., 2011). ...
The second millennium CE in Europe is known for both climatic extremes and bloody conflict. Europeans experienced the Medieval Warm Period and the Little Ice Age, and they suffered history-defining violence like the Wars of the Roses, Hundred Years War, and both World Wars. In this paper, we describe a quantitative study in which we sought to determine whether the climatic extremes affected conflict levels in Europe between 1,005 and 1980 CE. The study involved comparing a well-known annual historical conflict record to four published temperature reconstructions for Central and Western Europe. We developed a Bayesian regression model that allows for potential threshold effects in the climate–conflict relationship and then tested it with simulated data to confirm its efficacy. Next, we ran four analyses, each one involving the historical conflict record as the dependent variable and one of the four temperature reconstructions as the sole covariate. Our results indicated that none of the temperature reconstructions could be used to explain variation in conflict levels. It seems that shifts to extreme climate conditions may have been largely irrelevant to the conflict generating process in Europe during the second millennium CE.
... The Uchediya sequence's age bracket falls from 1395 to 1850 AD and coincides with the globally accepted transition phase of the Medieval Warm Period (MWP) to the Little Ice Age (LIA). The LIA is inconsistently defined between a broad time frame of 14th century (AD 1300-1400) and 19th century (AD 1850 and 1900) whereas, the MWP falls ∼1000-1300 AD (Crowley, 2000;Crowley and Lowery, 2000;Mann, 2002;Jones and Mann, 2004). Mostly, the onset of LIA is taken as 1440 AD and ends as late as 1920 AD. ...
Analyses of a fluvial sedimentary sequence from the lower reaches of the Narmada River establish a record of rhythmic cycles of sediment facies that represent floods during the late Holocene. The south-west Indian monsoon strongly influences the study area, and heavy rainfall or cyclones which originate from either the Bay of Bengal or the Arabian Sea, also affect the region. Optically stimulated luminescence dating places the 8 m thick sediment sequence in the climate transition phase which ranges from the Medieval Warm Period to the Little Ice Age. Multi-proxy analyses including high-resolution granulometry, magnetic susceptibility, ferromagnetic mineral concentration, facies major oxide geochemistry, and micro-fossil records (from two sedimentary units) are used to study these late Holocene flood events. The latter are characterised by multiple sediment facies, depositional events, changes in channel morphology, and distinctive flood signatures. Integration of these records enables to identify two distinct aggradations viz. phase I and phase II, as well as a relative change in channel morphology. The study describes 11 flooding events and their imprints over multi-proxy records. Historic documents and instrumental records from the town of Bharuch referring to floods, movement of channel sand, channel shallowing, and the dysfunction of the ancient port of Bharuch further validate the inferences drawn from the sedimentary sequence. The study exemplifies the need to use high resolution and multi-proxy studies to interpret paleoflood records and climate signatures in order to build archives of monsoonal rivers.
... The second warm phase recorded in the high-resolution stable isotope and Mg concentration data can be identified as the MWP. This period between 1.1 and 0.6 ka BP was relatively warm and humid [2,9,10,61,65]. A temperature reconstruction from several climate proxies on the extratropical continents of the northern Hemisphere indicated the highest temperatures during the MWP and the Twentieth Century [7]. Furthermore, Martín-Chivelet et al. [68] suggested that climate during the MWP was warmer than during the RWP and temperatures of both warm periods were higher than present-day temperatures. ...
The Late Holocene was characterized by several centennial-scale climate oscillations including the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period and the Little Ice Age. The detection and investigation of such climate anomalies requires paleoclimate archives with an accurate chronology as well as a high temporal resolution. Here, we present 230Th/U-dated high-resolution multi-proxy records (δ13C, δ18O and trace elements) for the last 2500 years of four speleothems from Bunker Cave and the Herbstlabyrinth cave system in Germany. The multi-proxy data of all four speleothems show evidence of two warm and two cold phases during the last 2500 years, which coincide with the Roman Warm Period and the Medieval Warm Period, as well as the Dark Ages Cold Period and the Little Ice Age, respectively. During these four cold and warm periods, the δ18O and δ13C records of all four speleothems and the Mg concentration of the speleothems Bu4 (Bunker Cave) and TV1 (Herbstlabyrinth cave system) show common features and are thus interpreted to be related to past climate variability. Comparison with other paleoclimate records suggests a strong influence of the North Atlantic Oscillation at the two caves sites, which is reflected by warm and humid conditions during the Roman Warm Period and the Medieval Warm Period, and cold and dry climate during the Dark Ages Cold period and the Little Ice Age. The Mg records of speleothems Bu1 (Bunker Cave) and NG01 (Herbstlabyrinth) as well as the inconsistent patterns of Sr, Ba and P suggests that the processes controlling the abundance of these trace elements are dominated by site-specific effects rather than being related to supra-regional climate variability.
... There are two common basic methods to reconstruct regional paleo-temperature series under the constraint of lacking sufficient data (Yang et al., 2002). One way is to compute the average of all available proxy series in a study area (Jones et al., 1998;Crowley and Lowery, 2000), and the other is to merge proxy records of several subregions by a specific area weight (Wang and Gong, 2000;Yang et al., 2002). It is important to notice that before averaging, each series should be standardized or calculated using the anomalies to homogenize the original variability of all series (Yang et al., 2002). ...
Quantitative palaeotemperature reconstruction is crucial for understanding the evolution of Earth’s climate and reducing uncertainty in future climate predictions. Clarifying the temperature change over the Tibetan Plateau (TP) during the Common Era is critical because it plays a vital role in the prediction of cryosphere changes in such regions under a future warming climate. In this paper, we report a comprehensive synthesis of currently available quantitative temperature records to refine the temperature history of the TP during the Common Era. To date, Common Era quantitative temperature reconstructions are sparse and mainly concentrated in the northeastern TP. Considering seasonal bias of the available quantitative temperature reconstructions, three different composite temperature records for TP were derived, namely the “Standardization” composite, the “Mean annual air temperature anomaly” composite, and the “Mean summer temperature anomaly” composite individually. All the integrated temperature series reveal the Medieval Climate Anomaly and the Little Ice Age, but the start and end timings of these multi-centennial-scale periods and their temperature amplitudes differ. There is strong seasonality in temperature variations on this high plateau, and the 20th century warming was characterized by rapid winter temperature increases, while summer temperatures displayed weak variations. Spatial analysis suggests a relatively consistent signal marking a warm TP during 600–1400 CE and a cold plateau during 1400–1900 CE. Large-scale trends in temperature history for the TP resemble those for China and the Northern Hemisphere. Many factors, such as seasonality of temperature proxies, might lead to uncertainty in the reconstructed series. The results highlight that it is of crucial importance to develop more seasonal temperature reconstructions to improve the reliability of quantitative paleoclimatic reconstructions based on geological records across the TP.
... Historical pine expansion starts during the warm medieval maximum [28,39]. Local historical sources suggest a growing human impact on forest cover as soon as the seventh and eighth centuries; however, deforestation increased mostly during the 10th-11th centuries. ...
A 4 m core was extracted from the center of a peatland located in the Drugeon valley (France). Thirteen radiocarbon dates were used to build a robust age model. Testate amoebae were used for reconstructing mire surface wetness. High-resolution pollen analysis of the sequence reconstructed 9 millennia of development of the peatland and its surrounding vegetation. During the early/middle Holocene (9500 to 5800 cal BP), warm conditions led to high evapotranspiration and low water levels. The vegetation history is characterized by the development of a Pinus and a mixed Quercus forest. From 5800 cal BP, testate amoebae show wetter conditions, indicating the onset of the cooler Neoglacial period. The cooling is also evidenced by the development of Abies and Fagus trees, replacing the oak forest. The first indicators of human impact appear at about 4800 cal BP, and indicators of farming activity remains very rare until ca. 2600 cal BP, at the beginning of the Iron Age. The development of the peatland responded to climatic fluctuation until 2600 cal BP, after which human impact became the main driver. The last millennium has been characterized by sudden drying and the spread of pine on the peatland.
... Este periodo cubre varias etapas de importancia arqueológica como son: el Clásico del 2000 al 1300 años cal AP (1-650 dC) y el Epiclásico 1300 a 1000 cal AP (650-950 dC) (Sugiura, 2009), incluyendo importantes eventos de variabilidad climática como la denominada sequía Maya 900-1000 años cal AP (850-950 dC) y la anomalía cálida medieval 1000-715 años cal AP (950-1300 dC) (Crowley y Lowery, 2000). ...
The sedimentary record from alpine Lake La Luna provided evidences of the vegetation dynamics and climate change during the last 6000 cal yr BP (calibrated years before present). A combination of analyses, including palynology, geochemistry and charcoal, allow inferring changes in the plants communities and the environment. The record starts with the establishment of alpine grasslands. According to the pollen spectra, coniferous and Quercus forests developed between 6000 and 4700 cal yr BP associated to humid conditions and low fire forests frequency events. By 4700 to 2000 cal yr BP drier environments with increases in fires frequency and high abundance of Pinus pollen is recorded. During the last 2000 cal yr BP changes in vegetation includes increases in Abies and reduction in Pinus pollen that point to humid environmental conditions during the Classic (1-650 AD), whereas during the Epiclassic (650-950 AD) and the Medieval Anomaly (950 a 1300 AD) the Pinus pollen increased suggesting drier conditions. Cold climates with reduced frequency of fires events are inferred during the Little Ice Age (1300-1850 AD). Presence of maize pollen in the pollen record gives evidence human activities in the area since 4680 cal yr BP.
Palynological analysis of surface soil and sub-surface sediments from the outwash plain of Hamtah Glacier, Lahaul-Spiti, India, has brought out the vegetation and climatic changes in the area during the last 1580 years. The arboreal and non-arboreal pollen ratio (AP/NAP) has been used to demarcate the different vegetation and climatic zones, complemented by the frequencies of the broad-leaved taxa. Lower values of thermophilous, broad-leaved arboreal taxa, indicate that the region experienced cold-arid conditions between 1580 and 1330 yr BP (AD 370–620); which can be related to the Dark Ages Cold Period (DACP). Thereafter, between 1330 and 950 yr BP (AD 620–1000), a rejuvenation of the broad-leaved elements reflects the initiation of a comparatively warm and moist phase, marking the Medieval Climatic Anomaly (MCA) in the region. The warm-moist phase was, however, short-lived, and from 950 yr BP to the Present (AD 1000 onwards), the region saw a return to cold-arid conditions, as evidenced by a sharp fall in the AP/NAP ratio. This cold-arid phase was, nevertheless, punctuated by a warm-moist period during 790 to 680 yr BP (AD 1160–1270), which marks the terminal phase of the MCA. After the termination of the MCA, the Little Ice Age (LIA) is well-marked in the area. The culmination of the long cold-arid regime is characterized by warmer conditions over the last 160 years, which is the manifestation of the Current Warm Period (CWP). Magnetic susceptibility (χlf) and sediment geochemistry (Weathering Index of Parker) were also attempted to have a multi-proxy approach, and show a general compatibility with the palynological data. The palaeoclimatic evidences suggest shorter warm periods and extended colder phases during the last 1580 years; in this high-altitude, cold-desert, Trans Himalayan region.
Temperature variability likely played an important role in determining the spread and productive potential of North America’s key prehispanic agricultural staple, maize. The United States Southwest (SWUS) also served as the gateway for maize to reach portions of North America to the north and east. Existing temperature reconstructions for the SWUS are typically low in spatial or temporal resolution, shallow in time depth, or subject to unknown degrees of insensitivity to low-frequency variability, hindering accurate determination of temperature’s role in agricultural productivity and variability in distribution and success of prehispanic farmers. Here, we develop a model-based modern analog technique (MAT) approach applied to 29 SWUS fossil pollen sites to reconstruct July temperatures from 3000 BC to AD 2000. Temperatures were generally warmer than or similar to those of the modern (1961–1990) period until the first century AD. Our reconstruction also notes rapid warming beginning in the AD 1800s; modern conditions are unprecedented in at least the last five millennia in the SWUS. Temperature minima were reached around 1800 BC, 1000 BC, AD 400 (the global minimum in this series), the mid-to-late AD 900s, and the AD 1500s. Summer temperatures were generally depressed relative to northern hemisphere norms by a dominance of El Niño-like conditions during much of the second millenium BC and the first millenium AD, but somewhat elevated relative to those same norms in other periods, including from about AD 1300 to the present, due to the dominance of La Niña-like conditions.
Climate change refers to long-term alterations in climate patterns across various regions of the world. As per the data availability and explanations given by different researchers, human exercises, particularly the burning of coal, deforestation, and the use of oil have increased the temperature of the Earth by significantly improving the engagement of heat-absorbing gases in the environment. The above-stated ratio will increase proportionally in the future. Therefore, climate change is one of our biggest global challenges, and urgent action must be taken to reduce greenhouse gas emissions, and adapt to its effects, and ensure a long and healthy life for all. This paper examines the different aspects of the effects of climate change on different ecosystem elements, such as air, water, plants, animals, and human beings, with a notable focus on economic aspects. Finally, to better understand the situation, data in this report were collected from different media platforms, research mechanisms, guideline papers, newspapers, and other references. This review paper considers climate change mitigation and transformation hovers worldwide in different sectors like human health, crop productivity, and the related economic impact. The conclusions emphasize that government monitoring is essential for the country's long-term growth through responsible resource management.
In the recent years, the growing concern to understand the impact of climate variability on various aspects of human civilizations have led to developing an understanding of proxy response according to change in the environmental conditions. Among various climate-sensitive proxies (e.g., geochemistry, pollens, biomarkers, grain size, etc.), the stable isotopes are the crucial component that not only helps us to understand the climate variability in the past, but also provides a detailed understanding of past meteorological variables such as temperature and precipitation, and vegetation response with changing hydrological conditions. The present study is focusing on the application of stable isotopes (δ13C, δ18O, δ15N and δD) in order to understand the climate variability since Pleistocene to present day conditions and provide a significant insight towards understanding the role of external (solar forcings), and internal forcing factors (teleconnections, such as El-Niño Southern Oscillation – ENSO, North Atlantic Oscillation – NAO) influencing the centennial to millennial-scale climate variability. Further, using case studies from the south Asian region, we have highlighted several challenges such as the impact of post-depositional changes and moisture pathways associated with the isotopic studies. This understanding will further provide better insights of isotope behaviour in natural archives in spatially varied terrains which is essential to decipher the temporal evolution of climate.
Notre-Dame de Paris, the so famous Catholic cathedral standing on Ile de la Cité in Paris, was partially destroyed by fire on April 15 of 2019. This unfortunate destruction miraculously spared a part of the frame and made these woods accessible to the scientific community. As scientists particularly interested in the isotopic composition of wood as memory of past climate and as a clock to the past, we will take advantage of this tragedy and give new life to the Notre Dame woods. In the context of a programmatic action, the δ¹³C and δ¹⁸O chronologies will open a window on the climate of the Middle Ages. They will allow rekindling the debate on the geographical extension of the MWP and, therefore, on its origin. The ¹⁴C record, at a yearly resolution, is expected to be implemented in the next ¹⁴C calibration curve and to be used to document past changes in ¹⁴C production resulting either from changes in solar activity or supernovae.
The Little Ice Age (LIA), which lasted from about 1250 to 1860 AD, was likely the coldest period of the last 8000 years. Using new documentary data and analyses of alpine glacier fluctuations, the complex transition from the Medieval Climate Anomaly to the LIA and the ensuing high variability of seasonal temperatures, are described and interpreted for Europe. The beginning of the LIA was likely different in both hemispheres. The low temperature average of the LIA is primarily due to the high number of cold winters. Conversely many summers were warm and dry.
Important triggers of the lower temperatures were, primarily, the numerous clusters of volcanic eruptions and the weak solar irradiance during the four prominent Grand Solar Minima: Wolf, Spörer, Maunder, and Dalton. The drop in temperature triggered the sea-ice–albedo feedback and led to a weakening of the Atlantic overturning circulation, possibly associated with a trend towards negative North Atlantic Oscillation indices.
The statistics of extreme events show a mixed picture. Correlations with forcing factors are weak, and can only be found in connection with the “Years without a Summer”, which very often occurred after large volcanic eruptions.
Coastal forests and wetlands play an important role in supporting biodiversity, protecting the hinterlands and shorelines from erosion and also contributing to carbon sequestration and freshwater storage. To reconstruct late Holocene vegetation and environmental dynamics in the coastal lowlands of northern Iran and to detect the possible role of climate, human and Caspian Sea level fluctuation on coastal ecosystems, multi-proxy analysis was applied on the sediment cores from the inland Eynak (EYK) lagoon and near coast Bibi Heybat (BBH) alder swamp. Results shows that in the last 170 years, strong reduction of alder forest occurred around Eynak lagoon, while an expansion occurred in the coastal area in the last 100 years. This indicates that human impact shifted from the near coast to elevated inland, which might be due to the raised water level from the Caspian Sea and the coastal area of BBH region was flooded by brackish water from the Caspian Sea, and was not so suitable for agriculture anymore. This study indicate that alder swamp extent is different between coastal and inland sites, suggesting that further studies of multiple records across the region are needed. Moreover, this study helps to distangle human impacts from wetland processes and thus will be an important contribution to effective climate mitigation and conservation strategies. This multi-proxy study presents important palynological records, which helps to understand past and future impacts of various drivers, such as climate, human impact and sea level changes on wetland ecosystems both regionally and globally.
This study presents a decadal to centennial scale late Holocene climate scenario from the Indian summer monsoon (ISM) dominant region of western Himalaya. The subsurface sediments analyzed for palynology, carbon isotope (δ¹³C) and magnetic susceptibility (χlf) were collected from the temperate and alpine meadows, respectively receiving high (low) and relatively low (high) amount of ISM (winter) precipitation. We could identify the dry and moist phases linked to respective weakening and strengthening of ISM. High frequency of steppe pollen (Ephedra, Amaranthaceae, Asteraceae, Brassicaceae) between 4.4 and 3.8 ka represented a dry phase, coeval to 4.2 ka global dry event. Subsequent low δ¹³C values and high pollen frequency of moist vegetation (Geraniaceae, Cyperaceae, Apiaceae, Ranunculaceae and pteridophytes) till ca. 0.9 ka suggested moist phase but with an intermittent dry episode ca. 2.9 − 2.5 ka, allowing rise of steppe taxa. Conditions ameliorated ca. 1.8 ka and further enhanced between 1.5 and 0.9 ka, corresponding to Medieval Warm Period. Sharp increase in δ¹³C values and steppe vegetation ca. 0.8 ka attributed to dryness that intensified between 0.6 and 0.3 ka and coincide with Little Ice Age (LIA) anomaly. The recorded dry (weak ISM) phases correspond well with the low solar irradiance and also support the teleconnection with north Atlantic circulations. Palynological data from both the valleys complement each other throughout late Holocene time. However, the valleys showed temporal inconsistency in their aridity peaks during LIA phase. This indicates response variability of the two physiographically different sites to summer and winter monsoon systems.
The representation of the thermal and hydrological states in Land Surface Models is important for a realistic simulation of land-atmosphere coupling processes. The available evidence indicates that the simulation of subsurface thermodynamics in Earth System Models is inaccurate due to a zero-heat-flux bottom boundary condition being imposed too close to the surface. In order to assess the influence of soil model depth on the simulated terrestrial energy and subsurface thermal state, sensitivity experiments have been carried out in piControl, historical and RCP scenarios. A deeper bottom boundary condition placement has been introduced into the JSBACH land surface model by enlarging the vertical stratification from 5 to 12 layers, thereby expanding its depth from 9.83 to 1416.84 m. The model takes several hundred years to reach an equilibrium state in stand-alone piControl simulations. A depth of 100 m is necessary, and 300 m recommendable, to handle the warming trends in historical and scenario simulations. Using a deep bottom boundary, warming of the soil column is reduced by 0.5 to 1.5 K in scenario simulations over most land areas, with the largest changes occurring in northern high latitudes, consistent with polar amplification. Energy storage is 3 to 5 times larger in the deep than in the shallow model and increases progressively with additional soil layers until the model depth reaches about 200 m. While the contents of Part I focus on the sensitivity of subsurface thermodynamics to enlarging the space for energy, Part II (Steinert et al. 2021) addresses the sensitivity to changing the space for water and improving hydrological and phase-change interactions.
Ambio is a leading journal in environmental science and policy, sustainable development, and human-environment interactions. The paper at hand aims to run a bibliometric analysis to inspect the main publications features of Ambio in Science Citation Index Expanded SCI-EXPANDED. For this scope, a bibliometric survey has been carried out to investigate the journal’s historic characteristics in the Web of Science (WoS) categories of environmental sciences and environmental engineering for Ambio from 1980 to 2019. These are the categories for which the journal has been indexed throughout the indexed time frame. The paper proposes technical and methodological innovations, including improvements in the methods and original characteristics analyzed. Documents published in Ambio were searched out from SCI-EXPANDED. Six publication indicators were applied to evaluate the publication performance of countries, institutes, and authors. Three citation indicators were used to compare publications. As a parameter, the journal impact factor contributor was applied to compare the most frequently cited publications. The journal impact factor contributing publications were also discussed. Results show that Sweden ranked top in six publication indicators and that the top three productive institutes were located in Sweden. A low percentage of productive authors emerged as a journal impact factor contributor. Similarly, a low relationship between the IF contributing publications and the highly cited publications was also found. Less than half of the top 100 highly cited publications in Ambio did not lie within the high impact in most the recent year of 2019. Three members of the advisory board in Ambio were the main productive authors. T.V. Callaghan contributed to most of the publications while papers published by J. Rockstrom as first and corresponding author contributed the most to the journal impact factor. An article authored by Steffen et al. (2007) scored the highest total citations in 2019.
Paleoclimate reconstructions for the western US show spatial variability in the timing, duration, and magnitude of climate changes within the Medieval Climate Anomaly (MCA, ca. 900–1350 CE) and Little Ice Age (LIA, ca. 1350–1850 CE), indicating that additional data are needed to more completely characterize late-Holocene climate change in the region. Here, we use dendrochronology to investigate how climate changes during the MCA and LIA affected a treeline, whitebark pine ( Pinus albicaulis Engelm.) ecosystem in the Greater Yellowstone Ecoregion (GYE). We present two new millennial-length tree-ring chronologies and multiple lines of tree-ring evidence from living and remnant whitebark pine and Engelmann spruce ( Picea engelmannii Parry ex. Engelm.) trees, including patterns of establishment and mortality; changes in tree growth; frost rings; and blue-intensity-based, reconstructed summer temperatures, to highlight the terminus of the LIA as one of the coldest periods of the last millennium for the GYE. Patterns of tree establishment and mortality indicate conditions favorable to recruitment during the latter half of the MCA and climate-induced mortality of trees during the middle-to-late LIA. These patterns correspond with decreased growth, frost damage, and reconstructed cooler temperature anomalies for the 1800–1850 CE period. Results provide important insight into how past climate change affected important GYE ecosystems and highlight the value of using multiple lines of proxy evidence, along with climate reconstructions of high spatial resolution, to better describe spatial and temporal variability in MCA and LIA climate and the ecological influence of climate change.
The chapter “Climate change before instrumental measurements” is a review and compilation of papers concerning the reconstruction of Poland’s climate in the last millennium. Data for this period are gaining importance due to their comparability with modern instrumental data, which is possible thanks to their high temporal resolution (annual, seasonal). The authors compiled the research results of climate reconstruction based on the following available data sources: direct man-made observations of weather and early instrumental measurements, dendrochronological records and varved sediment records. These three types of material are so far the best-known and best-developed proxy sources of past climate information, going back centuries in Poland. Generally, the chapter is divided into three parts presenting the results of climate reconstruction made with the above-mentioned data sources. On the basis of each method, the reconstructions of both air temperature and precipitation (including extreme rainfall and drought) for the winter and summer seasons are presented.
Lacustrine sediments from ice-free areas of Antarctica record both paleoecological and paleoclimatic information. Four sediment profiles (IIL1, IIL3, IIL4 and IIL9) were collected at Inexpressible Island, Ross Sea, to establish a robust late-Holocene chronology using accelerator mass spectrometry (AMS) ¹⁴C dating and geochemical and lithological analyses. The IIL1 and IIL4 sediments were strongly affected by penguin guano, and their bottom (oldest) ages were dated to 1659 and 4860 yr BP, respectively, using a Mixed Marine SoHem mode. By contrast, the organic matter of IIL3 and IIL9 sediments were predominantly sourced from aquatic microbial mats with the bottom ages of these two cores at 3179 and 2945 yr BP, respectively, based on a SHCal13 mode. The mass accumulation rates of the four sediment profiles inferred from this chronology showed peaks during ~1400–800 yr BP, corresponding to greater mean grain size and higher sand fraction ratios in the IIL3 and IIL9 profiles, suggesting strengthened hydrodynamic effect in this period. Our results indicate a relatively warm period occurred in the study area, in accordance with an ‘optimum’ warming in the Ross Sea region. From a regional view, this warm period was also consolidated with climatic records from the western Ross Sea, most likely corresponding to a well-recognized climate perturbation known as the Medieval Climate Anomaly (MCA) in many parts of the world.
The phenomenon of climate change is posing a serious threat to the overall integrity of our planet and to the existence of life on Earth. Climate change, however, is not a new phenomenon as far as the history of Earth is considered. All the previous events of climate change were driven by the natural causes, and the environment of Earth was gradually restored back to normal during the course of time. However, in the present scenario, climate change is completely driven by anthropogenic factors and is occurring at a very fast rate. The abrupt and extreme changes that are occurring in the environment are beyond the buffering capacity of Earth, and there does not seem to be any possibility that the situation will come back to normal. This chapter discusses the natural as well as anthropogenic causes of climate change and compares the past and the present scenario of climate change.
Recently, there has been a lot of discussion about the impact of climate change on human conflict. Here, we report a study in which we revisited the findings of a paper that has been cited many times in the discussion. The paper in question focused on the association between temperature and conflict in Europe between 1000 and 1980 CE and suggested that colder temperatures led to more conflict. However, there are reasons to be skeptical of this finding. Most importantly, the analytical technique used by the paper’s authors was not suitable for the conflict dataset because the dataset is count-based and contains autocorrelation. With this in mind, we developed a Bayesian time-series model that is capable of dealing with these features, and then we reanalysed the dataset in conjunction with several temperature reconstructions. The results we obtained were unambiguous. None of the models that included temperature as a covariate outperformed a null hypothesis in which conflict levels at any given time were determined only by previous levels. Thus, we found no evidence that colder temperatures led to more conflict in Europe during the second millennium CE. When this finding is placed alongside the results of other studies that have examined temperature and conflict over the long term, it is clear that the impact of temperature on conflict is context dependent. Identifying the factor(s) that mediate the relationship between temperature and conflict should now be a priority.
This work highlights the potential significance of palaeoclimate model outputs in explaining the physical processes and mechanisms to better understand the speleothem-based proxy records of the precipitation and temperature signals during the Indian northeast and southwest monsoon from 850 to 2000AD. Thus, discussion is mainly focused on this conception by providing insights for aligning modeling preferences with the proxy records. δ¹⁸O speleothem values show that precipitation over northeast India (NEI) remained constantly higher than that over the summer core monsoon zone (CMZ) from 850-2000AD. Based on the dynamical numerical coupled model (CSIRO-Mk3L-1–2) outputs, the data are in alignment with the presence of four proxy-based major extreme climatic events: Dry Century (DC), Medieval Climatic Anomaly (MCA), Extreme Dry Century (EDC) and Little Ice Age (LIA) during the last millennia. In these extremes a significant trend in diurnal temperature range (DTR), in particular, is correspondingly observed. These extremes and associated mechanisms are examined using surface energetics and corresponding atmospheric-oceanic coupled processes. The analysis of downward radiative (shortwave and longwave), latent and sensible heat fluxes provided better rationale and understanding of associated physical processes and mechanisms. It is found that the latent and sensible heat fluxes were balanced by downward radiative fluxes and the remaining part of energy was anomalously trapped inside the surface, thus reflecting anomalous climatic behavior during these extremes.
The sediment core collected at a water depth of 260.2 m off Mahanadi, western Bay of Bengal was analyzed for grain size fractions, clay minerals, and major and trace elements to understand changing depositional environments, source and processes with time, from ~ 2300 cal yr before present (BP) to the year of the collection (2014). Age was estimated using accelerator mass spectrometer (AMS) 14C dates of two planktonic foraminifera samples. The core was divided into six distinct zones based on the significant changes in the sediment components and clay minerals. The presence of higher than average clay and smectite and lower silt and illite, in Zone II (2000 years BP–1070 cal yr BP) and Zone V (300–130 cal yr BP) revealed their deposition in low energy conditions, while, Zone III (1070 to 530 cal yr BP) and Zone VI (132 cal yr BP to present) exhibited higher silt and illite and lower clay and smectite than average suggesting their deposition in a high energy environment. Similar depositional environments observed between Zones II and V and also between Zones III and VI indicated the reoccurrence of similar hydrodynamic conditions with time. Zone II represents the Roman Warm Period and part of the early Medieval Warm Period, while, zone V corresponds to the retreating phase of the Little Ice Age. High Al in zone III and fluctuating trend in zone VI indicates higher Al release along with silt and illite from physical weathering in a cold and arid climate, while, smectite showed a positive correlation with Ti indicating the source of Ti and smectite as basic igneous rocks released during the enhanced southwest monsoon and warm climate. Mn and Zn distribution revealed fluctuations in the Oxygen Minimum Zone (OMZ) intensity to changing hydrodynamic conditions and depositional environments. The present study revealed changing depositional environments in the western Bay of Bengal with time with respect to changing material influx, reflecting fluctuating monsoons and climate.
Global warming has had an unprecedented impact on environmental changes and thus human life in mid-high latitude regions. As one of the areas most affected by global warming, Northeast China has suffered from a series of ecological crises, including warming-induced water deficits, permafrost thaw, and extended growing seasons. The change in annual average temperature (annual T) variations in Northeast China since the Industrial Revolution are still not fully understood, mainly because of the lack of long-term instrumental data and high-resolution annual T reconstructions. Here, we present the first annual T reconstruction (r = −0.683, p < .001, n = 60) for 1818–2012 in Northeast China, which may also be the first temperature reconstruction based on tree-ring δ¹⁸O in China. The reconstruction is significantly related to temperature variations over mid-high latitude Eurasia and agree (p < .01) with several long-term hydroclimatic reconstructions in the surrounding area. When the internal variability in the reconstruction was high, the decadal to multidecadal cycles were significant. Further analysis found that the reconstruction was mainly affected by the East Asian Summer Monsoon (EASM) and North Atlantic Oscillation (NAO). The reconstruction was significantly negatively correlated with several time series of annual T in the Northern Hemisphere, which showed that there is a substantial difference in annual T between Northeast China and other regions of the Northern Hemisphere. The difference mainly existed before the 1950s. From the 1850s to the 1950s, the annual T in Northeast China decreased slightly. However, extreme warming began in the 1950s in Northeast China, and this warming has been unprecedented during the past two centuries. If the warming trend since the 1950s continues, then it will lead to devastating disasters to forest and permafrost ecosystems in Northeast China.
Temperature-depth profiles of boreholes of a region can be analysed to estimate the past variations in climate. Perturbations over the surface ground temperature are imparted deep into the Earth’s subsurface. Western Ghats regions of India are considered to be one of the most ecologically rich regions and also play a crucial role in deciding the climatological characteristics of the country. This study quantifies the possible climate warming or cooling in the past century in the Western Ghats using temperature-depth profiles of five boreholes in a depth range of 140–198 m located in Koyna region (17.38° N, 73.74° E) of Maharashtra state, India. The analysis shows that there has been a significant warming of 0.8 ± 0.2 °C over the past 100 years in the region. The inferred warming is comparable with the trends of meteorological records of the area which yields an increasing trend of 0.56 °C in the surface air temperature (SAT). For further validation of results, a combined study of borehole temperature profiles and surface air temperature (SAT) profiles was done which showed that the period was warmer than the earlier long-term temperature records of the region by 0.8 °C. This pre-observational mean (POM) value seems to be consistent with previously studied POMs over India. This study provides a ‘true estimate’ of climate change and can be used as a robust technique to reconstruct the past climate warming.
We studied a periglacial lake situated in the monsoon-dominated Central Himalaya where an interplay of monsoonal precipitation and glacial fluctuations during the late Holocene is well preserved. A major catastrophe occurred on 16–17 June 2013, with heavy rains causing rupturing of the moraine-dammed Chorabari Lake located in the Mandakini basin, Central Himalaya, and exposed 8-m-thick section of the lacustrine strata. We reconstructed the late-Holocene climatic variability in the region using multi-parametric approach including magnetic, mineralogical and chemical (XRF) properties of sediments, paired with grain size and optically simulated luminescence (OSL) dating. The OSL chronology suggests that the lake was formed by a lateral moraine during the deglaciation phase of Chorabari Glacier between 4.2 and 3.9 ka and thereafter the lake deposited about 8-m-thick sediment sequence in the past 2.3 ka. The climatic reconstruction of the lake broadly represents the late-Holocene glacial chronology of the Central Himalaya coupled with many short-term climatic perturbations recorded at a peri-glacial lake setting. The major climatic phases inferred from the study suggests (1) a cold period between 260 BCE and 270 CE, (2) warmer conditions between 900 and 1260 CE for glacial recession and (3) glacial conditions between ~1370 and 1720 CE when the glacier gained volume probably during the ‘Little Ice Age’ (LIA). We suggest a high glacial sensitivity to climatic variability in the monsoon-dominated region of the Himalaya.
Der Treibhauseffekt beruht auf der Absorption terrestrischer Infrarotstrahlung in der Erdatmosphäre. Wasserdampf reduziert die Transmissivität der Erdatmosphäre für Infrarotstrahlung in einem weiten Wellenlängenbereich und ist das wichtigste Treibhausgas. Kohlendioxid (CO2) hat ein Absorptionsmaximum bei 15 µm.
The South Pacific Subtropical High (SPSH) is a predominant feature of the South American climate. The variability of this high-pressure center induces changes in the intensity of coastal alongshore winds and precipitation, among others, over southwestern South America. In recent decades, strengthening and expansion of the SPSH have been observed and attributed to the current global warming. These changes have led to an intensification of the southerly winds along the coast of northern to central Chile and a decrease in precipitation from central to southern Chile. Motivated by improving our understanding about the regional impacts of climate change in this part of the Southern Hemisphere, we analyzed SPSH changes during the two most extreme climate events of the last millennium, the Little Ice Age (LIA) and the Current Warm Period (CWP: 1970–2000), based on paleoclimate records and CMIP5/PMIP3 model simulations. In order to assess the level of agreement of general circulation models, we also compare them with ERA-Interim reanalysis data for the 1979–2009 period as a complementary analysis. Finally, with the aim of evaluating future SPSH behavior, we include 21st century projections under a Representative Concentration Pathway (RCP8.5) scenario in our analyses. Our results indicate that during the relative warm (cold) period, the SPSH expands (contracts). Together with this change, alongshore winds intensify (weaken) south (north) of ∼35∘ S; also, southern westerly winds become stronger (weaker) and shift southward (northward). Model results generally underestimate reanalysis data. These changes are in good agreement with paleoclimate records, which suggest that these variations could be related to tropical climate dynamics but also to extratropical phenomena. However, although models adequately represent most of the South American climate changes, they fail to represent the Intertropical Convergence Zone–Hadley cell system dynamics, emphasizing the importance of improving tropical system dynamics in simulations for a better understanding of its effects on South America. Climate model projections indicate that changes recently observed will continue during the next decades, highlighting the need to establish effective mitigation and adaptation strategies against their environmental and socioeconomic impacts.
The Medieval Climate Anomaly (MCA, AD950-1250) is the most recent warm period lasting for several hundred years and is regarded as a reference scenario when studying the impact of and adaptation to global and regional warming. In this study, we investigated the characteristics of temperature variations on decadal-centennial scales during the MCA for four regions (Northeast, Northwest, Central-east, and Tibetan Plateau) in China, based on high-resolution temperature reconstructions and related warm-cold records from historical documents. The ensemble empirical mode decomposition method is used to analyze the time series. The results showed that for China as a whole, the longest warm period during the last 2000 years occurred in the 10th–13th centuries, although there were multi-decadal cold intervals in the middle to late 12th century. However, in the beginning and ending decades, warm peaks and phases on the decadal scale of the MCA for different regions were not consistent with each other. On the inter-decadal scale, regional temperature variations were similar from 950 to 1130; moreover, their amplitudes became smaller, and the phases did not agree well from 1130 to 1250. On the multi-decadal to centennial scale, all four regions began to warm in the early 10th century and experienced two cold intervals during the MCA. However, the Northwest and Central-east China were in step with each other while the warm periods in the Northeast China and Tibetan Plateau ended about 40–50 years earlier. On the multi-centennial scale, the mean temperature difference between the MCA and Little Ice Age was significant in Northeast and Central-east China but not in the Northwest China and Tibetan Plateau. Compared to the mean temperature of the 20th century, a comparable warmth in the MCA was found in the Central-east China, but there was a little cooling in Northeast China; meanwhile, there were significantly lower temperatures in Northwest China and Tibetan Plateau.
The evolution of temperatures during the Holocene is controversial, especially for the early Holocene. The occurrence of the Holocene Thermal Maximum (HTM) during the early Holocene has recently been reconsidered and seasonal biases have been suggested in the paleoclimatic proxies. High regional variability and a low number of reliable and continuous quantitative reconstructions compared with the oceanic realm further complicate study of the Holocene climate in the continental realm. We analyzed branched glycerol dialkyl glycerol tetraethers (brGDGTs), an organic paleothermometer, and palyno-logical signals as part of a multiproxy analysis of the sedimentary record from Lake St Front, in the Massif Central (France). Identification of a shift in brGDGT sources through the Holocene required removing terrigenous influences from the temperature signal. BrGDGT-and pollen-inferred paleotemperature reconstructions (based on the Modern Analog Technique and the Weighted Averaging Partial Least Squares method) were compared. Both showed a thermal maximum during the early Holocene followed by a decrease of temperatures. We evaluated biases which could potentially influence the reconstructed signal. There was no evidence for a summer temperature bias either for brGDGT-derived temperatures or for pollen-derived temperatures. The Lake St Front data, in agreement with other regional records, confirm the occurrence of the HTM as a general warm period during the early Holocene followed by mid-Holocene cooling in Western Europe and suggest that seasonal biases are not the main explanation of the Holocene conundrum d the disagreement between model simulations and proxy-based temperature reconstructions for the northern hemisphere.
Making use of EOF analysis and statistical optimal averaging techniques, the problem of random sampling error in estimating the global average temperature by a network of surface stations has been investigated. The EOF representation makes it unnecessary to use simplified empirical models of the correlation structure of temperature anomalies. If an adjustable weight is assigned to each station according to the criterion of minimum mean-square error, a formula for this error can be derived that consists of a sum of contributions from successive EOF modes. The EOFs were calculated from both observed data and a noise-forced EBM for the problem of one-year and five-year averages. The mean square statistical sampling error depends on the spatial distribution of the stations, length of the averaging interval, and the choice of the weight for each station data stream. Examples used here include four symmetric configurations of 4 × 4, 6 × 4, 9 × 7, and 20 × 10 stations and the Angell-Korshover configuration. Comparisons with the 100-yr U.K. dataset show that correlations for the time series of the global temperature anomaly average between the full dataset and this study's sparse configurations are rather high. For example, the 63-station Angell-Korshover network with uniform weighting explains 92.7% of the total variance, whereas the same network with optimal weighting can lead to 97.8% explained total variance of the U.K. dataset.
Climatic changes resulting from greenhouse gases will be superimposed on natural climatic variations. High-resolution proxy records of past climate can be used to extend our perspective on regional and hemispheric changes of climate back in time by several hundred years. Using historical, tree-ring and ice core data, we examine climatic variations during the period commonly called the 'Little Ice Age'. The coldest conditions of the last 560 years were between AD 1570 and 1730, and in the nineteenth century. Unusually warm conditions have prevailed since the 1920s, probably related to a relative absence of major explosive volcanic eruptions and higher levels of greenhouse gases.
A method is developed for estimating the uncertainty (standard error) of observed regional, hemispheric, and global-mean surface temperature series due to incomplete spatial sampling. Standard errors estimated at the grid-box level [SE 2 S 2 (1 r ¯)/(1 (n 1)r ¯)] depend upon three parameters: the number of site records (n) within each box, the average interrecord correlation (r ¯) between these sites, and the temporal variability (S 2) of each grid-box temperature time series. For boxes without data (n 0), estimates are made using values of S 2 interpolated from neighboring grid boxes. Due to spatial correlation, large-scale standard errors in a regional-mean time series are not simply the average of the grid-box standard errors, but depend upon the effective number of independent sites (N eff) over the region. A number of assumptions must be made in estimating the various parameters, and these are tested with observational data and complementary results from multicentury control integrations of three coupled general circulation models (GCMs). The globally complete GCMs enable some assumptions to be tested in a situation where there are no missing data; comparison of parameters computed from the observed and model datasets are also useful for assessing the performance of GCMs. As most of the parameters are timescale dependent, the resulting errors are likewise timescale dependent and must be calculated for each timescale of interest. The length of the observed record enables uncertainties to be estimated on the interannual and interdecadal timescales, with the longer GCM runs providing inferences about longer timescales. For mean annual observed data on the interannual timescale, the 95% confidence interval for estimates of the global-mean surface temperature since 1951 is 0.12C. Prior to 1900, the confidence interval widens to 0.18C. Equivalent values on the decadal timescale are smaller: 0.10C (1951–95) and 0.16C (1851–1900).
Fingerprint techniques for the detection of anthropogenic climate change aim to distinguish the climate response to anthropogenic
forcing from responses to other external influences and from internal climate variability. All these responses and the characteristics
of internal variability are typically estimated from climate model data. We evaluate the sensitivity of detection and attribution
results to the use of response and variability estimates from two different coupled ocean atmosphere general circulation models
(HadCM2, developed at the Hadley Centre, and ECHAM3/LSG from the MPI für Meteorologie and Deutsches Klimarechenzentrum). The
models differ in their response to greenhouse gas and direct sulfate aerosol forcing and also in the structure of their internal
variability. This leads to differences in the estimated amplitude and the significance level of anthropogenic signals in observed
50-year summer (June, July, August) surface temperature trends. While the detection of anthropogenic influence on climate
is robust to intermodel differences, our ability to discriminate between the greenhouse gas and the sulfate aerosol signals
is not. An analysis of the recent warming, and the warming that occurred in the first half of the twentieth century, suggests
that simulations forced with combined changes in natural (solar and volcanic) and anthropogenic (greenhouse gas and sulfate
aerosol) forcings agree best with the observations.
It has frequently been suggested that the period encompassing the ninth to the fourteenth centuries A.D. experienced a climate warmer than that prevailing around the turn of the twentieth century. This epoch has become known as the Medieval Warm Period, since it coincides with the Middle Ages in Europe. In this review a number of lines of evidence are considered, (including climate-sensitive tree rings, documentary sources, and montane glaciers) in order to evaluate whether it is reasonable to conclude that climate in medieval times was, indeed, warmer than the climate of more recent times. Our review indicates that for some areas of the globe (for example, Scandinavia, China, the Sierra Nevada in California, the Canadian Rockies and Tasmania), temperatures, particularly in summer, appear to have been higher during some parts of this period than those that were to prevail until the most recent decades of the twentieth century. These warmer regional episodes were not strongly synchronous. Evidence from other regions (for example, the Southeast United States, southern Europe along the Mediterranean, and parts of South America) indicates that the climate during that time was little different to that of later times, or that warming, if it occurred, was recorded at a later time than has been assumed. Taken together, the available evidence does not support a global Medieval Warm Period, although more support for such a phenomenon could be drawn from high-elevation records than from low-elevation records.
The available data exhibit significant decadal to century scale variability throughout the last millennium. A comparison of 30-year averages for various climate indices places recent decades in a longer term perspective.
Building on recent studies, we attempt hemispheric temperature reconstructions with proxy data networks for the past millennium. We focus not just on the reconstructions, but the uncertainties therein, and important caveats. Though expanded uncertainties prevent decisive conclusions for the period prior to AD 1400, our results suggest that the latter 20th century is anomalous in the context of at least the past millennium. The 1990s was the warmest decade, and 1998 the warmest year, at moderately high levels of confidence. The 20th century warming counters a millennial-scale cooling trend which is consistent with long-term astronomical forcing.
Spatially resolved global reconstructions of annual surface temperature
patterns over the past six centuries are based on the multivariate calibration
of widely distributed high-resolution proxy climate indicators. Time-dependent
correlations of the reconstructions with time-series records representing
changes in greenhouse-gas concentrations, solar irradiance, and volcanic aerosols
suggest that each of these factors has contributed to the climate variability
of the past 400 years, with greenhouse gases emerging as the dominant forcing
during the twentieth century. Northern Hemisphere mean annual temperatures
for three of the past eight years are warmer than any other year since (at
least) ad 1400.
Abstract. We review the surface air temperature
record of the past 150 years, considering the homogeneity
of the basic data and the standard errors of estimation
of the average hemispheric and global estimates.
We present global fields of surface temperature change
over the two 20-year periods of greatest warming this
century, 1925–1944 and 1978–1997. Over these periods,
global temperatures rose by 0.378 and 0.328C, respectively.
The twentieth-century warming has been accompanied
by a decrease in those areas of the world affected
by exceptionally cool temperatures and to a lesser extent
by increases in areas affected by exceptionally warm
temperatures. In recent decades there have been much
greater increases in night minimum temperatures than
in day maximum temperatures, so that over 1950–1993
the diurnal temperature range has decreased by 0.088C
per decade. We discuss the recent divergence of surface
and satellite temperature measurements of the lower
troposphere and consider the last 150 years in the context
of the last millennium. We then provide a globally
complete absolute surface air temperature climatology
on a 18 3 18 grid. This is primarily based on data for
1961–1990. Extensive interpolation had to be undertaken
over both polar regions and in a few other regions
where basic data are scarce, but we believe the climatology
is the most consistent and reliable of absolute surface
air temperature conditions over the world. The
climatology indicates that the annual average surface
temperature of the world is 14.08C (14.68C in the Northern
Hemisphere (NH) and 13.48C for the Southern
Hemisphere). The annual cycle of global mean temperatures
follows that of the land-dominated NH, with a
maximum in July of 15.98C and a minimum in January of
12.28C.
Analyses of underground temperature measurements from 358 boreholes in eastern North America, central Europe, southern Africa, and Australia indicate that, in the 20th century, the average surface temperature of Earth has increased by about 0.5 degreesC and that the 20th century has been the warmest of the past five centuries. The subsurface temperatures also indicate that Earth's mean surface temperature has increased by about 1.0 degreesC over the past five centuries. The geothermal data offer an independent confirmation of the unusual character of 20th-century climate that has emerged from recent multiproxy studies.
A Monte Carlo inverse method has been used on the temperature profiles measured down through the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland Ice Sheet, and the Dye 3 borehole 865 kilometers farther south. The result is a 50, 000-year-long temperature history at GRIP and a 7000-year history at Dye 3. The Last Glacial Maximum, the Climatic Optimum, the Medieval Warmth, the Little Ice Age, and a warm period at 1930 A.D. are resolved from the GRIP reconstruction with the amplitudes -23 kelvin, +2.5 kelvin, +1 kelvin, -1 kelvin, and +0.5 kelvin, respectively. The Dye 3 temperature is similar to the GRIP history but has an amplitude 1.5 times larger, indicating higher climatic variability there. The calculated terrestrial heat flow density from the GRIP inversion is 51.3 milliwatts per square meter.
Changes in the size of glaciers, in the altitude of the alpine tree-limit, and variation in the width of tree-rings during the Holocene clearly indicate that the average Scandinavian summer temperature has fluctuated. During warm periods it has been about 2°C warmer than at present; during cold periods it has been almost as cold as it was during the coldest decades of the previous centuries. Superimposed on these long-term variations, which have lasted from 100 to 200 years, are short fluctuations in temperature. The Scandinavian chronology, which is based on glacier and alpine tree-limit fluctuations as well as on dendrochronology, is well correlated with the changes in climate, which studies of ice cores from central Greenland have revealed. It is therefore believed that the Scandinavian climate chronology depicts conditions typical of a large area. The Scandinavian record is compared with data concerning solar irradiation variations estimated as 14C anomalies obtained from tree-rings. A correlation between major changes in climate and variations in solar irradiation points to a solar forcing of the climate. This means that there is no evidence of a human influence on climate so far.
Lichenometry and geological evidence permit establishment of a chronology of rock glacier development during Neoglaciation in the northern Sawatch Range. Portions of rock glaciers were assigned approximate absolute ages based on maximum thallus diameters of Rhizocarpon geographicum, Lecanora thomsonii, and Lecidea atrobrunnea. Values for the total percentage of lichen cover also aided in separating younger from older deposits. Although lichen growth-rate curves could not be constructed for the study area, a growth-rate curve for Rhizocarpon geographicum, developed in 1967 by Benedict for the Colorado Front Range, appears to be useful for dating rock surfaces in the northern Sawatch Range. Available data indicate that rock glacier development in four cirques was nearly synchronous during the last several thousand years. An early period of rock glacier development, here termed Temple Lake I, began more than 4,000 years ago and lasted for an unknown length of time. Temple Lake II deposits began to form between 3,750 and 3,500 years BP and continued to accumulate until about 2,500 years ago. Audubon rock glaciers began forming about 1,900 years BP and continued to develop until 1,000 to 900 years ago. Relative sizes of Temple Lake and Audubon rock glaciers indicate that processes and conditions favoring rock glacier formation during the Temple Lake stade were more intense and/or lasted longer than during the Audubon stade. The Gannett Peak stade of Neoglaciation is represented in the study area only by talus. This study supports earlier conclusions that Neoglaciation in the Rocky Mountains was characterized by three main intervals of glacier advance and/or rock glacier development. The Neoglacial record, however, is incomplete in the study area because no evidence was found of glacier or rock glacier activity during the Gannett Peak stade.
IN the current debate on the magnitude of modern-day climate change,
there is a growing appreciation of the importance of long, high-resolution proxies
of past climate13. Such records provide an indication of natural
(pre-anthropogenic) climate variability, either singly at specific geographical
locations or in combination on continental and perhaps even hemispheric
scales4. There are, however, relatively few records that are well
dated, of high resolution and of verifiable fidelity in terms of climate response,
and conspicuously few that extend over a thousand years or more5.
Here we report a tree-ring-based reconstruction of mean summer temperatures over the
northern Urals since AD 914. This record shows that the mean temperature of the
twentieth century (190190) is higher than during any similar period since AD
914.
Tree-ring data have been used to reconstruct the mean summer (April-August) temperature of northern Fennoscandia for each year from AD 500 to the present. Summer temperatures have fluctuated markedly on annual, decadal and century timescales. There is little evidence for the existence of a Medieval Warm Epoch, and the Little Ice Age seems to be confined to the relatively short period between 1570 and 1650. This challenges the popular idea that these events were the major climate excursions of the first millennium, occurring synchronously throughout Europe in all seasons. An analysis of past warming trends suggests that any summer warming induced by greenhouse gases may not be detectable in this region until after 2030.
Understanding the role of volcanic and solar variations in climate change is important not only for understanding the Little Ice Age but also for understanding and predicting the effects of anthropogenic changes in atmospheric composition in the twentieth century and beyond. The evaluate the significance of solar and volcanic effects, we use four solar reconstructions and three volcanic indices as forcings to an energy-balance model and compare the results with temperature reconstructions. Our use of a model representing the climate system response to solar and volcanic forcings distinguishes this from previous direct comparisons of forcings with temperature series for the Little Ice Age. Use of the model allows us to assess the effects of the ocean heat capacity on the evolution of the temperature response. Using a middle-of-the-road model sensitivity of 3°C for doubled CO2, solar forcings of less than 0.5% are too small to account for the cooling of the Little Ice Age. Volcanic forcings, in contrast, give climate responses comparable in amplitude to the changes of the Little Ice Age. A combination of solar and volcanic forcings explains much of the Little Ice Age climate change, but these factors alone cannot explain the warming of the twentieth century. The best simulations of the period since 1850 include anthropogenic, solar, and volcanic forcings.
The principal results of studies on historical climate change from A.D.
1000 to the present in China are reviewed. The studies are based on
analysis of local annals and court records. After discussing the
methodology of transferring descriptive accounts into quantitative
estimates of past climates, we summarize the main results, which are
generally substantiated by multiple lines of evidence: 1) There were
significant historical climate fluctuations in China, with a range of
about 1.0°-1.5°C in recent centuries. 2) Significant
decadal-scale warm fluctuations occurred during a cool interval broadly
correlative with the Little Ice Age. 3) There was an increased frequency
of both droughts and floods in some pans of China during the Little Ice
Age. Increased frequencies of dust storms accompanied the dry phases of
the cool periods. 4) The spatial pattern of some Little Ice Age
precipitation changes appears to reflect a modified development of
different phases of the summer monsoon. 5) As suggested by recent GCM
studies, enhanced Little Ice Age aridity may be due to increased winter
snow cover causing temperature and soil moisture feedbacks the following
spun 6) Although there is some agreement between climate change in China
and elsewhere, there are also indications that significant lap occur
between the timing and direction of climate change in different regions.
This pattern appears different from the warming trend of the past
century, which is more uniform in both hemispheres.
Oxygen isotope analysis of anew ice core from the crest of the Greenland ice sheet reveals a climatic record of the past 1,420 years. Climatic changes of medium frequencies are in phase with corresponding changes in Iceland and England, whilst long-term changes at mid Atlantic longitudes are out of phase with Europe and North America. Reconciliation with Norse history suggests a strong climatic impact, and a parallel is drawn to the present critical situation of the human society.
Observations of the Earth's near-surface temperature show a global-mean temperature increase of approximately 0.6 K since 1900 (ref. 1), occurring from 1910 to 1940 and from 1970 to the present. The temperature change over the past 30–50 years is unlikely to be entirely due to internal climate variability2, 3, ⁴ and has been attributed to changes in the concentrations of greenhouse gases and sulphate aerosols⁵ due to human activity. Attribution of the warming early in the century has proved more elusive. Here we present a quantification of the possible contributions throughout the century from the four components most likely to be responsible for the large-scale temperature changes, of which two vary naturally (solar irradiance and stratospheric volcanic aerosols) and two have changed decisively due to anthropogenic influence (greenhouse gases and sulphate aerosols). The patterns of time/space changes in near-surface temperature due to the separate forcing components are simulated with a coupled atmosphere–ocean general circulation model, and a linear combination of these is fitted to observations. Thus our analysis is insensitive to errors in the simulated amplitude of these responses. We find that solar forcing may have contributed to the temperature changes early in the century, but anthropogenic causes combined with natural variability would also present a possible explanation. For the warming from 1946 to 1996 regardless of any possible amplification of solar or volcanic influence, we exclude purely natural forcing, and attribute it largely to the anthropogenic components.
Tree-ring data have been used to reconstruct the mean summer (April-August) temperature of northern Fennoscandia for each year from AD 500 to the present. Summer temperatures have fluctuated markedly on annual, decadal and century timescales. There is little evidence for the existence of a Medieval Warm Epoch, and the Little Ice Age seems to be confined to the relatively short period between 1570 and 1650. This challenges the popular idea that these events were the major climate excursions of the first millennium, occurring synchronously throughout Europe in all seasons. An analysis of past warming trends suggests that any summer warming induced by greenhouse gases may not be detectable in this region until after 2030.
In the northeastern St. Elias Mountains in southern Yukon Territory and Alaska, C14-dated fluctuations of 14 glacier termini show two major intervals of Holocene glacier expansion, the older dating from 3300-2400 calendar yr BP and the younger corresponding to the Little Ice Age of the last several centuries. Both were about equivalent in magnitude. In addition, a less-extensive and short-lived advance occurred about 1250-1050 calendar yr BP (A.D. 700–900). Conversely, glacier recession, commonly accompanied by rise in altitude of spruce tree line, occurred 5975–6175, 4030-3300, 2400-1250, and 1050-460 calendar yr BP, and from A.D. 1920 to the present. Examination of worldwide Holocene glacier fluctuations reinforces this scheme and points to a third major interval of glacier advances about 5800-4900 calendar yrs BP; this interval generally was less intense than the two younger major intervals. Finally, detailed mapping and dating of Holocene moraines fronting 40 glaciers in the Kebnekaise and Sarek Mountains in Swedish Lapland reveals again that the Holocene was punctuated by repeated intervals of glacier expansion that correspond to those found in the St. Elias Mountains and elsewhere. The two youngest intervals, which occurred during the Little Ice Age and again about 2300–3000 calendar yrs BP, were approximately equal in intensity. Advances of the two older intervals, which occurred approximately 5000 and 8000 calendar yr BP, were generally less extensive. Minor glacier fluctuations were superimposed on all four broad expansion intervals; those of the Little Ice Age culminated about A.D. 1500–1640, 1710, 1780, 1850, 1890, and 1916. In the mountains of Swedish Lapland, Holocene mean summer temperature rarely, if ever, was lower than 1°C below the 1931–1960 summer mean and varied by less than 3.5°C over the last two broad intervals of Holocene glacial expansion and contraction.
Relationships between the stable isotope contents (δ2H, δ13C) in dendrochronologically dated tree rings of firs (Abies alba, Black Forest) and air temperature, relative humidity, as well as precipitation rate were investigated for the period 1959 to 1980. Only the late wood of each ring was used, since isotope data from early wood, grown during spring, does not unambiguously reflect the climate of the respective growth season. The δ13C-values, but not the δ2H-values show significant correlations with temperature, humidity, and precipitation. Based on this observation, δ13C-values were used to construct a paleoclimatic record for the past millenium. This required correction for anthropogenic 13C-inputs since about 1850. The reconstructed temperatures are largely in agreement with presently-accepted variations in the recent past, whereby a “climatic optimum” appears during the Early Middle Ages with August temperatures about 0.5 °C higher than today.
Temperatures for the past 2700 yr are estimated using well-dated pollen data from northwestern lower Michigan. The pollen data were sampled from sediment cores of four lakes along a 75-km transect, with fine-grained morainic soils around the two western lakes and sandy outwash soils around the lakes to the east. Climatic reconstructions based on the pollen data from the sandy sites show less temperature change than the reconstructions from the other sites, because variations in the composition of the vegetation at the sandy sites are edaphically restricted. One of the cores studied was dated by counting visible annual laminations (varves). The cores from the other lakes were dated based on three radiocarbon dates per core as well as the historically determined age of the settlement horizons. All the time scales were cross-checked using pollen-stratigraphic correlation between the four sites. A calibration function was developed using a network of modern pollen and climate data covering all of lower Michigan. Based on this calibration function, the 2700-yr reconstruction for Marion Lake indicates an estimated growing-season temperature range of 1.3°C between extreme 30-yr means. Mild conditions persisted prior to ca. A.D. 400, but a cold interval occurred between ca. A.D. 500 and 800. The well-marked warm period evident from ca. A.D. 1000 to 1200 was the last time when temperatures were about equal to the 1931–1960 mean. A prolonged longed cooling occurred after A.D. 1200 and reached 1°C below the 1931–1960 mean by the 1700s. A warming of 0.5°C is indicated from ca. A.D. 1750 to 1850. The estimated temperatures for the 1830s at Marion Lake agree with the instrumental data for that period and this provides some validation of the calibration-function results.
Measured 18O/16O ratios from the Greenland Ice Sheet Project 2 (GISP2) ice core extending back to 16,500 cal yr B.P. provide a continuous record of climate change since the last glaciation. High-resolution annual 18O/16O results were obtained for most of the current millennium (A.D. 818-1985) and record the Medieval Warm Period, the Little Ice Age, and a distinct 11-yr 18O/16O cycle. Volcanic aerosols depress central Greenland annual temperature (∼1.5°C maximally) and annual 18O/16O for about 4 yr after each major eruptive event. On a bidecadal to millennial time scale, the contribution of solar variability to Holocene Greenlandic temperature change is ∼0.4°C. The role of thermohaline circulation change on climate, problematic during the Holocene, is more distinct for the 16,500-10,000 cal yr B.P. interval. (Analogous to 14C age calibration terminology, we express time in calibrated (cal) yr B.P. (A.D. 1950 = 0 cal yr B.P.)). The Oldest Dryas/Bølling/Older Dryas/Allerød/Younger Dryas sequence appears in great detail. Bidecadal variance in 18O/16O, but not necessarily in temperature, is enhanced during the last phase of lateglacial time and the Younger Dryas interval, suggesting switches of air mass transport between jet stream branches. The branched system is nearly instantaneously replaced at the beginning of the Bølling and Holocene (at ∼14,670 and ∼11,650 cal yr B.P., respectively) by an atmospheric circulation system in which 18O/16O and annual accumulation initially track each other closely. Thermodynamic considerations of the accumulation rate-temperature relationship can be used to evaluate the 18 O/16O-temperature relationship. The GISP2 ice-layer-count years of major GISP2 climate transitions also support the use of coral 14C ages for age calibration.
Spatial anomalies of tree-ring chronologies can provide information on high-frequency spatial anomalies in paleoclimate representing droughts, colder-than-normal intervals, and other synoptic-scale features. Examples are presented in which 65 tree-ring chronologies are calibrated with spatial anomalies in North American meteorological records of seasonal temperature and precipitation, and with sea-level pressure over the North American and North Pacific sectors. Multivariate transfer functions are obtained that scale and convert the past spatial variations in the tree-ring record into estimates of past variations in the meteorological record. Objective verifications of the reconstructions are obtained using independent meteorological observations for time periods other than those used in the calibration. Historical information or other proxy data from the 19th century are also used for verifying the decadal (or longer) and regional reconstructions and for identifying strengths and weaknesses of the various sources of information. The reconstructed winter and summer temperatures for the United States and southwestern Canada and winter precipitation for the Columbia Basin and California during the 17th through 19th centuries were found to differ from the 20th century means with large-scale variations evident. Extreme winters similar to 1976–1977 are also identified and found to be more frequent in the past, especially in the 17th century. The climatic reconstructions in this time domain are dominated by high-frequency, synoptic-scale fluctuations that can be interpreted as cyclonic-scale changes in atmospheric circulation. Such reconstructions may be useful for testing various climatic models and estimates developed primarily from 20th-century meteorological data against the longer estimated record for the 17th through 19th centuries.
Moraines and rock glaciers in Front Range cirques record at least four, and possibly five, intervals of Holocene glacier expansion. The earliest and most extensive was the Satanta Peak advance, which deposited multiple terminal moraines near present timberline shortly before 9915 ± 165 BP. By 9200 ± 135 BP, timberline had risen to at least its modern elevation; by 8460 ± 140 BP, patterned ground on Satanta Peak moraines had become inactive. Although a minor ice advance may have occurred just prior to 7900 ± 130 BP, there is no evidence that glaciers or perennial snowbanks survived in the Front Range during the “Altithermal” maximum (ca. 7500–6000 BP), or during a subsequent interval of alpine soil formation (ca. 6000–5000 BP).
Glaciers were larger during the Triple Lakes advance (5000–3000 BP) than at any other time during Neoglaciation. Minimum ages of 4485 ± 100 BP, 3865 ± 100 BP, and ca. 3150 BP apply to a threefold sequence of Triple Lakes deposits in Arapaho Cirque. After an important interval of soil formation and cavernous weathering, glaciers and rock glaciers of the Audubon advance (1850–950 BP) reoccupied many cirques, and perennial snowbanks blanketed much of the area above present timberline; although the general Audubon snow cover had begun to melt from valley floors by 1505 ± 95 BP, expanded snowbanks lingered on tundra ridge crests until 1050–1150 BP, and glaciers persisted is sheltered cirques until at least 955 ± 95 BP. Following a minor interval of ice retreat, glaciers of the Arapaho Peak advance (300–100 BP) deposited multiple moraines in favorably oriented cirques.
Interpretation of Holocene glacial deposits in the Southern and Central Rocky Mountains has been hampered by (1) a heavy reliance upon relative-dating criteria, many of which are influenced by factors other than age; (2) the assumption that glacial advances in high-altitude cirques can be correlated directly with alluvial deposition in far-distant lowlands; and (3) the assumption that glacial advances have necessarily been synchronous throughout the Rocky Mountain region and the world. Although Holocene glacier fluctuations in the Front Range are believed to reflect changes in regional climate, the Front Range chronology does not have particularly close analogs in other parts of North America. Better-dated local sequences are needed before the hypothesis of global synchroneity can be adequately evaluated; until synchroneity has been proven, long-distance correlations and worldwide cycles of recurring glaciation will remain unconvincing.
Ice cores from the tropics and subtropics, in conjunction with those from the polar regions, provide a multifaceted record (dust, chemistry, stable isotopes, accumulation) of environmental changes which can be viewed both spatially and temporally. This paper emphasizes the oxygen isotopic record (δ18O) preserved in cores from the poles to the tropics and assesses the evidence for global warming in the last 50–100 years. From north to south these records include: Camp Century, Greenland, Dunde and Guliya Ice Caps, China, Gregoriev Ice Cap, Kirghizia (formerly part of USSR), Quelccaya Ice Cap, Peru and Siple Station and South Pole, Antarctica. The central Asian records along with that from Quelccaya provide strong evidence of recent and rapid warming in the tropics and subtropics. For the Dunde Ice Cap, where a long paleoclimatic record is available, the warming in this century appears to be unprecedented in the Holocene. These tropical and subtropical records contrast sharply with those from polar cores which show little evidence of a recent warming. These data suggest that either the recent warming is a middle and lower latitude phenomenon or that these high altitude tropical and subtropical glaciers may be more sensitive to climate changes than the massive polar ice sheets. Regardless, the current rapid disintegration of many tropical and subtropical glaciers may result in the permanent loss of numerous unique archives.
Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbon-dated box core show that SST was approximately 1°C cooler than today approximately 400 years ago (the Little Ice Age) and 1700 years ago, and approximately 1°C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation.
Times of Feast, Times of Famine Farrar, Strauss, and Giroux
- Roy Le
- E Ladurie
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