Climate sensitivity and regional climate change patterns
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With regard to the response of the climate system to changes in atmospheric composition and associated radiative properties, two core aspects were tested. The first parameter addressed was climate sensitivity, which describes by how many degrees the equilibrium global mean temperature will rise if the CO2-equivalent concentration of greenhouse gases in the atmosphere doubles compared to the pre-industrial level. The simple climate model in the Atmosphere-Ocean System (AOS) of IMAGE 2, attuned to represent the generally accepted central estimate for the climate sensitivity of 2.5 degrees, was adjusted to explore the range from 1.5 to 4.5 degrees. As expected, this amplified or reduced all climate-related impacts very tightly for any given emission projection. For climate change impacts, however, global mean effects are of limited significance. Therefore, a second sensitivity analysis addressed the spatial patterns of temperature and precipitation projections. IMAGE employs exogenous patterns from complex climate models (GCMs) to scale the impacts of the endogenously derived global mean temperature change. The robustness of regional impacts on different GCM patterns was tested by UNEP/RIVM (2004). Results indicate that while GCM outcomes for some regions are fairly consistent, in other regions the temperature effect is very different. With regard to annual precipitation the disagreement between models is even stronger. In some regions, e.g. South America, they do not even agree on the direction of change. |
