Browsing by Author "Kröger, Anni"

Earth’s energy budget describes the balance between the net incoming and outgoing energy fluxes, and the energy balance approach can be used to better understand the basic physical mechanisms of climate change. Anthropogenic changes in the atmospheric composition, such as increases in greenhouse gases, drive changes in climate system which in turn can cause rising of the global temperatures. Various feedbacks, associated with increase in atmospheric water vapor content, changes in clouds and reduced snow/ice cover, affect the pattern of surface warming by altering the fluxes of energy. By studying the energy balance at the top of the atmosphere and at the surface, we gain useful information about the climate system’s response to changes in the atmospheric composition. In this thesis, data for 23 climate models in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) was used. The present-day distributions and future projections of the simulated changes (under RCP8.5 emission scenario, Representative Concentration Pathway) for 14 radiative and non-radiative energy budget components, along with the changes in surface temperature and cloud cover were studied, with baseline period of 1981-2010 and a comparison scenario period of 2071-2100. The geographical distributions of the multimodel mean changes and their global averages were analysed. Additionally, the intermodel consistency of the simulated changes was studied with the intermodel standard deviations and the ratio of multimodel mean change to the intermodel standard deviation. Furthermore, the intermodel correlation between the change in surface temperature and each energy budget variable was discussed. A general finding was that the multimodel mean surface temperature increases everywhere, more over land than oceans, and that the warming is amplified over the northern polar regions. The changes were largest for the thermal radiation fluxes, and the dominating contribution to the surface warming was concluded to be the change in clear- sky atmospheric re-radiation component. However, increase in absorbed shortwave radiation, presumably due to reduced ice/snow cover and increase in atmospheric water vapor content, was also found to be substantial, and there was a strong negative correlation between the clear-sky downward shortwave radiation flux and the change in temperature over the low-to-mid latitudes. The comparison of contribution of the changes in longwave and shortwave fluxes to global warming in the near-future and long-term climate model projections could be an interesting subject for future studies. Additionally, the changes in the surface energy fluxes were found to modify the pattern of surface warming.