Modeling and diagnosing changes in radiation and surface energy balance

The primary anthropogenic interference with climate occurs through a perturbation of the Earth radiation balance in response to human induced changes in atmospheric greenhouse gas and aerosol concentrations. Here we use global and regional climate models as well as comprehensive observational datasets to investigate the role of both natural and anthropogenic radiative forcings in the context of climate change. Our emphasis thereby lies on the radiative forcings at the surface, which critically influence various other components of the climate system, such as the hydrological cycle, biosphere growth or glacier melt. The spatial focus is on global down to European and Alpine scales.

Support:
These studies are supported by the NCCR Climate. The climate modeling part of these studies is supported by generous computational resources provided by the Swiss Center for Scientific Computing (CSCS).

Selected research topics:

Decadal changes in surface solar radiation (“global dimming/brightening”)

Recent studies present evidence that observed solar radiation reaching the ground has not been stable over time, but underwent significant decadal variations. These include a decrease of surface solar radiation ("global dimming") from the 1950s to the 1980s and a more recent recovery ("global brightening", Wild et al. 2005, Wild 2009).

In order to reproduce these trends in climate models and estimate their impacts on other components of the climate system, the inclusion of sophisticated schemes of aerosol and cloud microphysics are essential. Such schemes are implemented in the latest versions of the ECHAM5-HAM and CLM model series available at ETH. Transient experiments are carried out with these extended modeling systems to investigate the origins, magnitude and impacts of global dimming and brightening. These modelling studies are accompanied by diagnostic studies based on observational records from the Global Energy Balance Archive maintained in this group.

Contact: Martin Wild, Doris Folini, Marc Chiacchio, Knut Makowski,Christoph Schär

Selected publications:

Wild, M., Gilgen, H., Roesch, A., Ohmura, A., Long, C., Dutton, E., Forgan, B., Kallis, A., Russak, V., and Tsvetkov, A., 2005: From dimming to brightening: Decadal changes in solar radiation at the Earth’s surface. Science, 308, 847-850.

Norris, J.R., and Wild, M., 2006: Trends in direct and indirect aerosol radiative effects over Europe inferred from observed solar “dimming” and “brightening”, J. Geophys. Res. 112, D08214, doi:10.1029/2006JD007794.

Wild, M., 2009: How well do the IPCC AR4/CMIP3 models simulate global dimming and brightening and related effects on 20th century day- and nighttime warming? J. Geophys. Res., 114, D00D11, doi:10.1029/2008JD011372.

Wild, M., Trüssel, B., Ohmura, A., Long, C.N. König-Langlo G., Dutton, E.G., and Tsvetkov, A., 2009: Global Dimming and Brightening: an update beyond 2000. J. Geophys. Res., 114, D00D13, doi:10.1029/2008JD011382.

Mercado, L.M., Bellouin, N., Sitch, S., Boucher, O., Huntingford, C., Wild,^, M., and Cox, P.M., 2009: Impact of Changes in Diffuse Radiation on the Global Land Carbon Sink. Nature, 458, 1014-1018.

Wild, M., 2009: Global dimming and brightening: A review. J. Geophys. Res. 114, D00D16, doi:10.1029/2008JD011470.

Changes in surface radiation balance and the hydrological cycle

Radiative energy available at the Earth's surface is the principal driver of the hydrological cycle. Variations in the surface radiation balance thus induce changes in evapotranspiration as well as precipitation, and thereby govern the intensity of the global hydrological cycle. Recent evidence suggests that significant anthropogenic variations occur in both solar and thermal radiation reaching the Earth’s surface, driven by changes in air pollution and greenhouse gas emissions, respectively (see above). These variations may affect the strength of the hydrological cycle. We investigate the link between the radiation balance and the intensity of the hydrological cycle using both global and regional climate models as well as comprehensive observational databases, such as the Global Energy Balance Archive. A particular focus will be placed on Europe, where the changes in surface energy and water are best documented.

Contact: Martin Wild, Christoph Schär, 

Selected publications:

Wild, M., Dümenil, L., and Schulz, J.P., 1996: Regional climate simulation with a high resolution GCM: surface hydrology. Climate Dynamics, 12, 755-774.

Wild, M., Ohmura, A., Gilgen, H., and Rosenfeld, D., 2004: On the consistency of trends in radiation and temperature records and implications for the global hydrological cycle. Geophys. Res. Lett., 31, L11201, doi: 10.1029/2003GL019188.

Wild, M., Grieser, J. and Schär, C., 2008: Combined surface solar brightening and greenhouse effect support recent intensification of the global land-based hydrological cycle. Geophys. Res. Lett., 35, L17706, doi:10.1029/2008GL034842.

Changes in surface radiative forcing, global warming and the diurnal temperature range

To disentangle the influence of surface solar and thermal radiation on global warming, the diurnal temperature range (DTR) is a promising quantity. Thereby we use the fact that solar and thermal radiation have different effects on the diurnal temperature range. Since the solar flux is only in effect during daylight, it affects the daily maximum temperature more than daily minimum temperature. The nighttime minimum temperature, on the other hand, is mainly affected by the thermal radiative exchanges. Nighttime surface radiative cooling depends on the capacity of the atmosphere to absorb and re-emit thermal radiation towards the surface. We analyse the evolution of DTR in global and regional (European) observational datasets as well as in transient global and regional climate model simulations, to determine the role of solar and thermal forcings in the context of global warming.

Contact: Martin Wild, Knut Makowski

Publications:

Wild, M., Ohmura A., Makowski, K., 2007: Impact of global dimming and brightening on global warming. Geophys. Res. Lett., 34, L04702, doi:10.1029/2006GL028031.

Makowski, K., Wild, M., and Ohmura, A., 2008: Diurnal temperature range over Europe between 1950 and 2005, Atmos. Chem. Phys., 8, 6483-6498.

Makowski, K., Jäger, E., Chiacchio, M., Wild, M., Ewen, T., and Ohmura, A., 2009: On the relationship between diurnal temperature range and surface solar radiation in Europe, J. Geophys. Res., 114, D00D07, doi:10.1029/2008JD011104.

Radiation and surface energy budgets in global and regional models

Substantial uncertainties exist in the distribution of radiative energy within the climate system and its representation in climate models. Particularly, the partitioning of energy absorption between the atmosphere and surface, and between the cloud-free atmosphere and clouds is insufficiently established and currently disputed. We combine the comprehensive surface observations available at ETH with top of atmosphere measurements to investigate this issue in global and regional climate models. Related diagnostic projects have been carried out in the framework of the Atmospheric Model Intercomparison Project (AMIP) and the IPCC 4th Assessment Report (AR4) Coupled Model Intercomparsion Project (CMIP3) as well as the forthcoming CMIP5 for the 5th Assessment Report (AR5). The aim is to gain a deeper insight into the processes that determine the distribution of radiative energy in the climate system, as a guideline to model improvement. An additional focus is on the non-radiative components of the surface energy balance in climate models, particularly on the latent heat flux, which is crucial for the link between the surface energy and water balance. The GEBA database provides a useful source of information for these studies.

Contact: Martin Wild

Selected publications:

Wild, M., Ohmura, A., Gilgen, H., and Roeckner, E., 1995a: Validation of GCM simulated radiative fluxes using surface observations. J. Climate, 8, 1309-1324.

Wild, M., Ohmura, A., Gilgen, H., and Roeckner, E., 1995b: Regional climate simulation with a high resolution GCM: surface radiative fluxes. Climate Dynamics, 11, 469-486

Wild, M., A. Ohmura, H. Gilgen, E. Roeckner, M. Giorgetta and J.J. Morcrette, 1998: The disposition of radiative energy in the global climate system: GCM-calculated versus observation estimates. Climate Dynamics, 14, 853-869.

Wild, M., 1999: Discrepancies between model-calculated and observed atmospheric shortwave absorption in areas with high aerosol loadings. J. Geophys. Res., 104 (D22), 27361-27371.

Wild, M., Ohmura, A., Gilgen, H., Morcrette, J.J., and Slingo, A., 2001: Downward longwave radiation in General Circulation Models. J. Climate, 14, 3227-3239.

Wild, M., 2005: Solar radiation budgets in atmospheric model intercomparisons from a surface perspective. Geophys. Res. Lett., 32, L07704, doi:10.1029/ 2005GL022421.

Wild, M., Long, C.N., and Ohmura, A., 2006: Evaluation of clear-sky solar fluxes in GCMs participating in AMIP and IPCC-AR4 from a surface perspective. J. Geophys. Res., 111, D01104, doi:10.1029/2005JD006118.

Wild, M., and Roeckner, E., 2006: Radiative fluxes in ECHAM5. J. Climate, 19, 3792-3809.

Wild, M., 2008: Shortwave and longwave surface radiation budgets in GCMs: a review based on the IPCC-AR4/CMIP3 models. Tellus, 60, 932 - 945. doi: 10.1111/j.1600-0870.2008.00342.x