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

• Published in: Environmental Research Letters
• Main Authors: Moreno-Chamarro, E, Caron, L-P, Ortega, P, Loosveldt Tomas, S, Roberts, M J
• Other Authors: Horizon 2020 Framework Programme, Met Office Hadley Centre Climate Programme funded by BEIS and Defra
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2021
• Subjects: North Atlantic
• Online Access: http://dx.doi.org/10.1088/1748-9326/abf28a; https://iopscience.iop.org/article/10.1088/1748-9326/abf28a; https://iopscience.iop.org/article/10.1088/1748-9326/abf28a/pdf

Abstract 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 ∼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° 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°) 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 ∼100 km resolution models could be underestimating the precipitation increase over Europe in winter and, consequently, the related potential risks.