Both temperature and precipitation output from all GCMs' twentieth century simulations have been found to be satisfactory representations of current climate in terms of mean geographical patterns, if analyzed at large scales (Raisanen 2007; Randall et al. 2007). Trend patterns are consistent with observations for those models that are forced by all known sources: volcanic eruptions, solar irradiance, greenhouse gases and aerosols (Barnett et al. 2005). Projected future warming patterns are robust (Meehl et al. 2007b), but global temperature change is uncertain by approximately 50% (Knutti et al. 2008) due to carbon cycle uncertainties (Friedlingstein et al. 2006) and models differing in their feedbacks and climate sensitivities (Bony et al. 2006, Knutti and Hegerl 2008). Short-term projections are better constrained by the observed warming than long-term projections (Knutti et al. 2002; Stott and Kettleborough 2002). This is because the effect of feedbacks amplifies with time and so do inter-model differences, so that differences across models become larger the farther in the future projections are. Models project changes in precipitation, extreme events (Tebaldi et al. 2006) and many other aspects of the climate system that are consistent with our understanding of climate processes and the consequences of a significant human influence on the climate, but agreement between models deteriorates as one moves from continental to regional to local (i.e. grid point) scales, and from mean quantities to more complex indices of climate events.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.