How certain are projections of the future European summer climate? And can this uncertainty be reduced? Researchers from Wageningen University investigated the uncertainty in an ensemble of regional climate model simulations. Confronting these models with observations of heat exchanges at the land surface allowed for a reduction in uncertainty. The largest reduction was obtained in regions where the land surface has an important effect on the summer climate.
Rising atmospheric concentrations of greenhouse gases are adding more energy to the Earth system, but how that extra energy turns to heat—and where that heating takes place—depends in part on regional variations in how the atmosphere and the land surface interact. Based on a historically high susceptibility to natural climate variability, driven in part by such land surface-atmosphere interactions, researchers expect Europe to be more strongly affected by climate change than some other regions.
Model vs. observation
To reduce uncertainty in projections of European regional warming Stegehuis et al. use modern measurements of land surface-atmosphere processes to constrain a series of 15 regional climate models. In general, heat exchange between the atmosphere and the land surface occurs in one of two ways. Latent heat exchange is when energy is used to drive processes that don't result in a change in temperature, such as evaporating water or melting ice and snow. Sensible heat exchange is a convective transfer of energy that results in a temperature change. Though researchers know that both latent and sensible heat exchange are important for controlling regional temperatures, these processes have not before been used to constrain regional models.
In the present study, the authors used observations of sensible heat flux to identify the best-performing regional climate models. They found that for central and northern Europe, warming by the end of the century may be as much as 1 Kelvin higher than the 2 to 6 degrees of warming that previous research suggested. But, for the Mediterranean and Balkans, previous work may have overestimated warming. By constraining future temperature projections with realistic sensible heat flux values the authors reduced the uncertainty in those calculations by up to 40% for regions with strong land surface-atmosphere coupling.
The paper by Stegehuis et al., written as part of an MSc thesis project at Wageningen University, was published in Geophysical Research Letters. It was selected by the editors of GRL as an AGU research spotlight.
Annemiek I. Stegehuis, Adriaan J. Teuling, Philippe Ciais, Robert Vautard and Martin Jung (2013). Future European temperature change uncertainties reduced by using land heat flux observations. Geophys. Res. Lett. doi:10.1002/grl.50404