Past long-term summer warming over western Europe in new generation climate models: role of large-scale atmospheric circulation

Julien Boé,Sybren Drijfhout,Katja Lohmann,Alessio Bellucci,Malcom Roberts,Laurent Terray,Retish Senan,Marie-Pierre Moine,Enrico Scoccimarro,Rein Haarsma,Sophie Valcke,Jon Seddon,Dian A Putrasahan,Klaus Wyser,Chris Roberts

doi:10.1088/1748-9326/ab8a89

Abstract

Past studies have concluded that climate models of previous generations tended to underestimate the large warming trend that has been observed in summer over western Europe in the last few decades. The causes of this systematic error are still not clear. Here, we investigate this issue with a new generation of climate models and systematically explore the role of large-scale circulation in that context.As an ensemble, climate models in this study warm less over western Europe and warm more over eastern Europe than observed on the 1951–2014 period, but it is difficult to conclude this is directly due to systematic errors given the large potential impact of internal variability. These differences in temperature trends are explained to an important extent by an anti-correlation of sea level pressure trends over the North Atlantic / Europe domain between models and observations. The observed trend tends to warm (cool) western (eastern) Europe but the simulated trends generally have the opposite effect, both in new generation and past generation climate models. The differences between observed and simulated sea level pressure trends are likely the result of systematic model errors, which might also impact future climate projections. Neither a higher resolution nor the realistic representation of the evolution of sea surface temperature and sea ice leads to a better simulation of sea level pressure trends.

Highlights

In the last few decades, western Europe has warmed faster than the global average (Bhend and Whetton 2013)
Future SLP changes strongly project on 1951–2014 trends for the vast majority of individual models (figure 6(b)). These results strongly suggest that both SLP trends over the North Atlantic / Europe domain on the 1951–2014 period and future changes in summer are shaped to an important extent by external forcings
Since the mid-20th century, a large warming trend has been observed over western Europe in summer

Summary

Introduction

In the last few decades, western Europe has warmed faster than the global average (Bhend and Whetton 2013). Van Oldenborgh et al (2009), analysing climate models from the Coupled Model Intercomparison Phase 3 project (CMIP3, Meehl et al 2007), have concluded that ‘Western Europe is warming much faster than expected’, especially in summer. Have concluded that the summer temperature trends over western Europe are underestimated in a large number of both CMIP3 and CMIP5 (Taylor et al 2012) models. For both Van Oldenborgh et al (2009) and Bhend and Whetton (2013) these differences between models and observations are likely the result of systematic model errors rather than internal variability. A systematic underestimation of the forced warming signal could have major implications for future climate and impact projections over western Europe

Methods

Results

Conclusion