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Fig. lla, b. The first EOF for annually-averaged near-surface temperature change in the a EIN and b SZA experiments Weight
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Due to restrictions in the available computing resources and a lack of suitable observational data, transient climate change experiments with global coupled ocean-atmosphere models have been started from an initial state at equilibrium with the present day forcing. The historical development of greenhouse gas forcing from the onset of industrializa...
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... Because of the large computer-time requirements of models, it is not always possible to perform a very long spin-up before starting an experiment with an AOGCM. Nevertheless, it is generally considered that starting a simulation devoted to analysing climate in the 20th and 21st centuries from a state representative of the pre-industrial climate (for instance 1850) allows problems related to initial conditions to be minimized (Fichefet and Tricot, 1992; Cubasch et al., 1995; Keen and Murphy, 1997). This appears to be valid for a large part of the world, but it may not be for the Southern Ocean because of the delayed response of the climate system at those latitudes, even at the surface. ...
Using the three-dimensional coarse-resolution climate model ECBILT-CLIO, 1000-year long ensemble simulations with natural and anthropogenic forcings have been performed to study the long-term variation of the ice cover in the Southern Ocean. Over the last 250 years, the ice area has decreased by about 1 × 106 km2 in its annual mean. A comparison with experiments driven by only natural forcings suggests that this reduction is due to both natural and anthropogenic forcing, the latter playing a larger role than natural forcing over the last 150 years. Despite this contribution from anthropogenic forcing, the simulated ice area at the end of the 20th century is similar to that simulated during the 14th century because of the slow response of the Southern Ocean to radiative forcing. Sensitivity experiments performed with the model show that the model's initial conditions have a large influence on the simulated ice cover and that it is necessary to start simulations at least two centuries before the period of interest in order to remove this influence. Copyright © 2005 Royal Meteorological Society.
... T21), and then provided as prescribed lower boundary conditions for an integration in a highresolution (e.g. T106) atmospheric model (CUBASCH et al. 1995). The equilibrium response of the high resolution model run is taken as a regional climate estimate. ...
... T21), and then provided as prescribed lower boundary conditions for an integration in a highresolution (e.g. T106) atmospheric model (CUBASCH et al. 1995). The equilibrium response of the high resolution model run is taken as a regional climate estimate. ...
... The atmospheric winter circulation over the North Atlantic area and the NAO winter index are good predictors of the structure of the macrofauna communities in the following spring. Models which simulate climate-change scenarios are able to reproduce the past and predict the future NAO winter index ( Cubasch et al. 1995, Hasselmann et al. 1995). Therefore, possible future developments of macrozoobenthos communities can be predicted for the next decades from those scenarios, and conclusions for long-term changes can drawn. ...
A multivariate regression model using observed climate data is used to forecast the climate-induced changes in macrozoobenthos in spring. This is demonstrated by a forecast over 6 yr of biomass, abundance and species number of macrozoobenthos communities in the southern North Sea. The partial linearity between climate and benthic variables, as well as the existence of a phase lag between climate variability during winter time and the response in macrozoobenthos in spring, makes the climate-induced variability in macrozoobenthos predictable. The results indicate that a major part of interannual and interdecadal variability of marine ecosystem, here demonstrated for macrozoobenthos, can be attributed to the physical forcing of winter climate.
... In the case of the anthropogenic sulfate aerosol (SUL) forcing, column depths from 8 latitude bands are used, deduced from anthropogenic sulfur dioxide (SO 2 ) emission data (Charlson et al. 1991). These are the same data used by Cubasch et al. (1995). However, an EOF decomposition (details see Section 3.1) of these time series reveals that using the first 3 PCs 99.9% of the total variance is explained. ...
Observed global and European spatiotemporal related fields of surface air temperature, mean-sea-level pressure and precipitation are analyzed statistically with respect to their response to external forcing factors such as anthropogenic greenhouse gases, anthropogenic sulfate aerosol, solar variations and explosive volcanism, and known internal climate mechanisms such as the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). As a first step, a princi- pal component analysis (PCA) is applied to the observed spatiotemporal related fields to obtain spa- tial patterns with linear independent temporal structure. In a second step, the time series of each of the spatial patterns is subject to a stepwise regression analysis in order to separate it into signals of the external forcing factors and internal climate mechanisms as listed above as well as the residuals. Finally a back-transformation leads to the spatiotemporally related patterns of all these signals being intercompared. Two kinds of significance tests are applied to the anthropogenic signals. First, it is tested whether the anthropogenic signal is significant compared with the complete residual variance including natural variability. This test answers the question whether a significant anthropogenic cli- mate change is visible in the observed data. As a second test the anthropogenic signal is tested with respect to the climate noise component only. This test answers the question whether the anthro- pogenic signal is significant among others in the observed data. Using both tests, regions can be specified where the anthropogenic influence is visible (second test) and regions where the anthro- pogenic influence has already significantly changed climate (first test).
... Recently some investigations , using forcing conditions from a time slice experiment (Cubasch et al. 1995), have been carried out for the North Sea (Kauker 1999, Langenberg et al. 1999) in order to investigate the influence of predicted climate change on the sea level of the North Sea. 'Time slice experiments' are carried out with high resolution global atmospheric models that are integrated for a relatively short period, using initial and boundary conditions from long-term integrations with coarse climate models. ...
Using a coupled ice/ocean model, an impact study on the influence of increased westerly winds in the North Sea and Baltic Sea due to strengthening of the polar front was carried out, as part of the German research project KLINO (Modelling inter-annual variability of hydrographic conditions in the North Sea and the Baltic Sea). By means of a simple sensitivity experiment it could be shown that the impact of a positive westerly wind anomaly (i.e. high North Atlantic Oscillation Index, NAO) results in an intensification of the cyclonic circulation in both the Baltic Sea and the North Sea, However, the impact on salt exchange and content is opposite for the 2 shelf seas: exchange between the North Sea and the North Atlantic increases with intensified westerly wind forcing and thus the North Sea salt content increases; for the Baltic Sea, the intensification of westerly winds inhibits exchange with the Kattegat. In combination with the increased doming of the lower layer (i.e. saltier) water in the center of the cyclonic eddies, and thus intensified vertical mixing, an overall decrease of salt content in the Baltic Sea and an erosion of the permanent halocline result. Thus, as it is expected that future climate, under the influence of increased atmospheric CO2 concentration, will lead to an intensification of the NAO, it was concluded that expected anthropogenic climate change will result in a weakening of haline stratification and a decrease in the salt content of the Baltic Sea.
... Such patterns can be derived from climate models. For instance, experiments with climate models (e.g., Cubasch et al., 1995) indicate that the ongoing increase of greenhouse gas concentrations in the atmosphere will lead to a general warming of the air near to the surface, with stronger warming over the continents and delayed warming over the ocean; the delay is, according to the model, particularly evident over the northwestern part of the North Atlantic. Figure 8 displays the warming as calculated by the climate model after 100 years of continuous increase (about 1% per year) of the CO 2 concentration. ...
Climate is largely determined by the fluid flows in the atmosphere and oceans. These flows are governed by the laws of fluid dynamics and thermodynamics. These laws are partial differential equations that represent the conservation of mass, momentum, energy and other quantities.1 If we could solve these equations, with the right initial and boundary conditions, then we would have the answers to all the pressing questions of the current climate debate. This, however, is not possible. Even if there were a unique set of such equations the only consensus about them is that they are highly and multiply nonlinear. They couple processes across all scales, from the planetary scales of wind and current systems to the micro-scales of molecular diffusion. The resulting flow is turbulent, with everything depending on everything else. It is also impossible to know the exact initial and boundary conditions, such as the exact shape of the continents or the details of human land use.
... Such patterns can be derived from climate models. For instance, experiments with climate models (e.g., Cubasch et al., 1995) indicate that the ongoing increase of greenhouse gas concentrations in the atmosphere will lead to a general warming of the air near to the surface, with stronger warming over the continents and delayed warming over the ocean; the delay is, according to the model, particularly evident over the northwestern part of the North Atlantic. Figure 8 displays the warming as calculated by the climate model after 100 years of continuous increase (about 1% per year) of the CO 2 concentration. ...
Climate is largely determined by the fluid flows in the atmosphere and oceans. These flows are governed by the laws of fluid dynamics and thermodynamics. These laws are partial differential equations that represent the conservation of mass, momentum, energy and other quantities.1 If we could solve these equations, with the right initial and boundary conditions, then we would have the answers to all the pressing questions of the current climate debate. This, however, is not possible. Even if there were a unique set of such equations the only consensus about them is that they are highly and multiply nonlinear. They couple processes across all scales, from the planetary scales of wind and current systems to the micro-scales of molecular diffusion. The resulting flow is turbulent, with everything depending on everything else. It is also impossible to know the exact initial and boundary conditions, such as the exact shape of the continents or the details of human land use.
... Here, the evaluation performed by Langenberg et al. (1999) is repeated with the results of the OPYC model for 15 yr (1979 to 1993) and for the high resolution time slice experiment of the '2 × CO 2 ' scenario of the German Climate Computing Centre (Bengtsson et al. 1995, Cubasch et al. 1995. The results of the 2 different models are compared and differences are evaluated with respect to the relevance of different processes for an accurate assessment of sea level variations. ...
... In Figs. 2 & 3, for the OPYC model, the same analysis as before is shown for the case of a thermal expansion of the Atlantic Ocean by about 10 cm, assumed to be realistic for the time of doubled atmospheric carbon dioxide concentrations (Cubasch et al. 1995). While there is an increase in the winter mean values, roughly by the same amount that the sea level was raised at the open boundaries (i.e. 10 cm), the deviations between mean and extremes (Fig. 3) are negligible for most coastal points. ...
Two models of the North Sea are compared with respect to their performance in the assessment of sea level changes in a changing climate: the OPYC model, originally designed as a global ocean model and run in a regional version, and the HAMSOM, which was built as a shelf sea model and applied to an extended region in a simplified version. Both models agree very well in their hindcast skill as measured by correlation and explained variance. The reaction of both models to the '2 x CO2' and 'control' runs of the time slice experiments of the DKRZ (German Climate Computing Center) is also very similar and indicates an increase of up to 30 cm of winter mean sea levels and no significant (compared with the variability in the past) impact an the intra-monthly 90 % quantiles. It is concluded that sea level is a rather robust parameter that could still be assessed with some confidence if both models were simplified further.
... Large-scale distributions of pressure, temperature, winds and precipitation are well represented spatially and seasonally. In recent years, GCM climate models are being applied extensively to analyses of transient or time-dependent variations in climate change (Cubasch et al., 1992Cubasch et al., , 1995 IPCC, 1992 IPCC, , 1996a Manabe and Stouer, 1993; Meehl et al., 1993 Meehl et al., , 1994 Mitchell et al., 1995a, b; Santer et al., 1994 Santer et al., , 1995 Haywood et al., 1997; Le Treut et al., 1998). Although GCMs and coupled models are attractive for these purposes, complex models are computationally costly, sometimes dicult to understand, and require high resolution data inputs, which in some cases simply does not exist. ...
Only recently, within a few decades, have we realized that humanity significantly influences the global environment. In the early 1980s, atmospheric measurements confirmed basic concepts developed a decade earlier. These basic concepts showed that human activities were affecting the ozone layer. Later measurements and theoretical analyses have clearly connected observed changes in ozone to human-related increases of chlorine and bromine in the stratosphere. As a result of prompt international policy agreements, the combined abundances of ozone-depleting compounds peaked in 1994 and ozone is already beginning a slow path to recovery. A much more difficult problem confronting humanity is the impact of increasing levels of carbon dioxide and other greenhouse gases on global climate. The processes that connect greenhouse gas emissions to climate are very complex. This complexity has limited our ability to make a definitive projection of future climate change. Nevertheless, the range of projected climate change shows that global warming has the potential to severely impact human welfare and our planet as a whole. This paper evaluates the state of the scientific understanding of the global change issues, their potential impacts, and the relationships of scientific understanding to policy considerations.
