Can we trust CMIP5/6 future projections of European winter precipitation?

IPCC models project a likely increase in winter precipitation over northern Europe under a high-emission scenario. These projections, however, typically rely on relatively coarse similar to 100 km resolution models that can misrepresent important processes driving precipitation, such as extratropical cyclone activity, and ocean eddies. Here, we show that a pioneering 50 km atmosphere-1/12 degrees ocean global coupled model projects a substantially larger increase in winter precipitation over northwestern Europe by mid-century than lower-resolution configurations. For this increase, both the highest ocean and atmosphere model resolutions are essential: only the eddy-rich (1/12 degrees) ocean projects a progressive northward shift of the Gulf Stream. This leads to a strong regional ocean surface warming that intensifies air-sea heat fluxes and baroclinicity. For this then to translate into a strengthening of North Atlantic extratropical cyclone activity, the 50 km atmosphere is essential, as it enables enhanced diabatic heating from water vapor condensation and an acceleration of the upper-level mean flow, which weaken vertical stability. Our results suggest that all recent IPCC climate projections using traditional similar to 100 km resolution models could be underestimating the precipitation increase over Europe in winter and, consequently, the related potential risks.

Automated summary

The use of a higher resolution atmosphere-ocean coupled model can more accurately predict an increase in winter precipitation over northern Europe, with traditional 100 km resolution models potentially underestimating the risk of precipitation increase in winter in Europe.