The Mediterranean climate change hotspot in the CMIP5 and CMIP6 projections

Pierre-Antoine Bretonnière,Francisco Doblas-Reyes,Martin Jury,Margarida Samsó,Raül Marcos,Josep Cos

doi:10.5194/esd-13-321-2022

Abstract

Abstract. The enhanced warming trend and precipitation decline in the Mediterranean region make it a climate change hotspot. We compare projections of multiple Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 6 (CMIP6) historical and future scenario simulations to quantify the impacts of the already changing climate in the region. In particular, we investigate changes in temperature and precipitation during the 21st century following scenarios RCP2.6, RCP4.5 and RCP8.5 for CMIP5 and SSP1-2.6, SSP2-4.5 and SSP5-8.5 from CMIP6, as well as for the HighResMIP high-resolution experiments. A model weighting scheme is applied to obtain constrained estimates of projected changes, which accounts for historical model performance and inter-independence in the multi-model ensembles, using an observational ensemble as reference. Results indicate a robust and significant warming over the Mediterranean region during the 21st century over all seasons, ensembles and experiments. The temperature changes vary between CMIPs, CMIP6 being the ensemble that projects a stronger warming. The Mediterranean amplified warming with respect to the global mean is mainly found during summer. The projected Mediterranean warming during the summer season can span from 1.83 to 8.49 ∘C in CMIP6 and 1.22 to 6.63 ∘C in CMIP5 considering three different scenarios and the 50 % of inter-model spread by the end of the century. Contrarily to temperature projections, precipitation changes show greater uncertainties and spatial heterogeneity. However, a robust and significant precipitation decline is projected over large parts of the region during summer by the end of the century and for the high emission scenario (−49 % to −16 % in CMIP6 and −47 % to −22 % in CMIP5). While there is less disagreement in projected precipitation than in temperature between CMIP5 and CMIP6, the latter shows larger precipitation declines in some regions. Results obtained from the model weighting scheme indicate larger warming trends in CMIP5 and a weaker warming trend in CMIP6, thereby reducing the difference between the multi-model ensemble means from 1.32 ∘C before weighting to 0.68 ∘C after weighting.

Highlights

The Mediterranean region (10◦ W, 40◦ E, 30◦ N, 45◦ N; Iturbide et al, 2020) is located between the arid and warm northern African climate and the humid and mild European climate (Cramer et al, 2018)
Apart from the figures displayed and the Supplement, additional ones generated during the study can be found in a shiny app in the following link https: //earth.bsc.es/shiny/medprojections-shiny_app/
The inter-model spread for the precipitation projections is large for all ensembles and usually has both negative and positive trends (e.g. DJF Coupled Model Intercomparison Project Phase 5 (CMIP5) precipitation trends range from −0.092 to 0.097 mm d−1 decade−1 for the 5th and 95th percentiles respectively)

Summary

Introduction

The Mediterranean region (10◦ W, 40◦ E, 30◦ N, 45◦ N; Iturbide et al, 2020) is located between the arid and warm northern African climate and the humid and mild European climate (Cramer et al, 2018). Global warming is not homogeneous, and Lionello and Scarascia (2018) suggests that the Mediterranean region is a climate change hotspot. The observed warming in the Mediterranean region during the last decades is expected to continue and grow larger than the global-mean warming (Lionello and Scarascia, 2018). Characteristics of the projected Mediterranean climate change have been linked to thermodynamic sources such as land–ocean warming contrast and lapse rate change in summer (Brogli et al, 2019), and to dynamical processes such as the changes in upper-tropospheric large-scale flow in winter (Tuel and Eltahir, 2020)

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Discussion

Conclusion