Radiation and the Hydrological Cycle on Global Scales

The primary anthropogenic interference with climate occurs through a perturbation of the global energy balance in response to human induced changes in atmospheric greenhouse gas and aerosol concentrations. The main focus of this research domain is thus on the global energy balance and its spatiotemporal variation. For this purpose we use global and regional climate models as well as comprehensive observational datasets in order to investigate the distribution of the energy fluxes in the climate system and the relation between the energy and water cycles on global to regional scales. Special emphasis is placed on variations in surface radiative energy which states the key driver of the global water cycle. There is indeed increasing evidence from direct observations that the surface radiative fluxes undergo significant changes on decadal timescales, not only in the thermal spectral range as expected from the increasing greenhouse effect, but also in the amount of solar radiation that reaches the Earth’s surface. A major issue is the detected multidecadal variations of surface solar radiation, with a decrease from the 1950s to the 1980s  ("global dimming") and its partial recovery thereafter ("brightening"). We also explore the consequences of these variations for various aspects of climate change, such as global warming, the intensity of the global water cycle, biosphere growth or glacier melt. On a more applied level, the impact of changes in solar resources on future solar power generation and on agricultural production are investigated.

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