Editing IPCC:AR6/WGI/Chapter-10 (section)

==== 10.6.4.6 Future Climate Information From Global Simulations ====

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The Mediterranean is expected to be one of the most prominent and vulnerable climate change hotspots ( [[#Diffenbaugh--2012|Diffenbaugh and Giorgi, 2012]] ). CMIP5, CMIP6, HighResMIP and CORDEX ( [[#10.6.4.7|Section 10.6.4.7]] ) simulations all project a future warming for the 21st century that ranges between 3.5°C and 8.75°C for RCP8.5 at the end of this century for those ending at 2100 (Figure 10.21a, b). CMIP6 results project more pronounced warming than CMIP5 for a given emissions scenario and time period (Figure 10.21c; [[#Coppola--2020|Coppola et al., 2020]] ). However, when analysing the Mediterranean warming in terms of mean global warming levels, the two ensembles largely agree, showing that summer warming is projected to reach values up to 40–50% larger than the global annual warming, largely independent of models and emissions scenarios (Figure 10.21d). Large regional differences exist, with enhanced warming projected over Turkey, the Balkans, the Iberian Peninsula and North African regions (Figures 10.14a, 10.21c; [[#Almazroui--2020a|Almazroui et al., 2020a]] ) and reaching, locally, values of up to double the global mean ( [[#Lionello--2018|Lionello and Scarascia, 2018]] ). The enhanced summer warming also increases the amplitude of the seasonal cycle ( [[#Yettella--2018|Yettella and England, 2018]] ).

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[[File:007e4c2219b09c7224cd75140ad29075 IPCC_AR6_WGI_Figure_10_20.png]]

'''Figure''' '''10.20 |''' '''Aspects of Mediterranean summer warming.''' '''(a)''' Mechanisms and feedbacks involved in enhanced Mediterranean summer warming. '''(b)''' Locations of observing stations in E-OBS and [[#Donat--2014|Donat et al. (2014)]] . '''(c)''' Differences in temperature observational datasets (NOAA Global Temp, Berkeley Earth, CRUTEM4 and GISTEMP) with respect to E-OBS for the land points between the Mediterranean Sea and 46°N and west of 30°E. '''(d)''' Observed summer (June to August) surface air temperature linear trends (°C decade <sup>–1</sup> ) over the 1960–2014 period from Berkeley Earth. '''(e)''' Time series of area averaged Mediterranean (25°N–50°N, 10°W–40°E) land point summer temperature anomalies (°C, baseline 1995–2014). Dark blue, brown and turquoise lines show low-pass filtered temperature of Berkeley Earth, CRU TS and HadCRUT5, respectively. Orange, light blue and green lines show low-pass filtered ensemble means of HighResMIP (4 members), CORDEX EUR-44 (20 members) and CORDEX EUR-11 (37 members). Blue and red lines and shadings show low-pass filtered ensemble means and standard deviations of CMIP5 (41 members) and CMIP6 (36 members). The filter is the same as the one used in Figure 10.10. '''(f)''' Distribution of 1960–2014 Mediterranean summer temperature linear trends (°C decade <sup>–1</sup> ) for observations (black crosses), CORDEX EUR-11 (green circles), CORDEX EUR-44 (light blue circles), HighResMIP (orange circles), CMIP6 (red circles), CMIP5 (blue circles) and selected SMILEs (grey box-and-whisker plots, MIROC6, CSIRO-Mk3-6-0, MPI-ESM and d4PDF). Ensemble means are also shown. CMIP6 models showing a very high ECS (Box. 4.1) have been marked with a black cross. All trends are estimated using ordinary least-squares and box-and-whisker plots follow the methodology used in Figure 10.6. '''(g)''' Ensemble mean differences with respect to the Berkeley Earth linear trend for 1960–2014 (°C decade <sup>–1</sup> ) of CMIP5, CMIP6, HighResMIP, CORDEX EUR-44 and CORDEX EUR-11. Further details on data sources and processing are available in the chapter data table (Table 10.SM.11).

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[[File:d024a23587bfc4b1a98f1def61fbd518 IPCC_AR6_WGI_Figure_10_21.png]]

'''Figure 10.''' '''21 |''' '''Projected Mediterranean summer warming. (a)''' Time series of area averaged Mediterranean (25°N–50°N, 10°W–40°E) land point summer surface air temperature anomalies (°C, baseline period is 1995–2014). Orange, light blue and green lines show low-pass filtered ensemble means of HighResMIP (highres-future, four members), CORDEX EUR-44 (RCP8.5, 20 members) and CORDEX EUR-11 (RCP8.5, 37 members). Blue and dark red lines and shadings show low-pass filtered ensemble means and standard deviations of CMIP5 (RCP8.5, 41 members) and CMIP6 (SSP5-8.5, 36 members). The filter is the same as the one used in Figure 10.10. The box-and-whisker plots show long-term (until 2081–2100) temperature changes of different CMIP6 scenarios with respect to the baseline period (SSP1-2.6 in dark blue, SSP2-4.5 in yellow, SSP3-7.0 in red, SSP5-8.5 in dark red). '''(b)''' Distribution of 2015–2050 Mediterranean summer temperature linear trends (°C per decade) for CORDEX EUR-11 (RCP8.5, green circles), CORDEX EUR-44 (RCP8.5, light blue circles), HighResMIP (highres-future, orange circles), CMIP6 (SSP5-8.5, dark red circles), CMIP5 (RCP8.5, blue circles) and selected SMILEs (grey box-and-whisker plots, MIROC6, CSIRO-Mk3-6-0 and MPI-ESM). Ensemble means are also shown. CMIP6 models showing a very high ECS (Box 4.1) have been marked with a black cross. All trends are estimated using ordinary least-squares and box-and-whisker plots follow the methodology used in Figure 10.6. '''(c)''' Projections of ensemble mean 2015–2050 linear trends (°C per decade) of CMIP5 (RCP8.5), CORDEX EUR-44 (RCP8.5), CORDEX EUR-11 (RCP8.5), CMIP6 (SSP5-8.5) and HighResMIP (highres-future). All trends are estimated using ordinary least-squares. '''(d)''' Projected Mediterranean summer warming in comparison to global annual mean warming of CMIP5 (dashed lines, RCP2.6 in dark blue, RCP4.5 in light blue, RCP6.0 in orange and RCP8.5 in red) and CMIP6 (solid lines, SSP1-2.6 in dark blue, SSP2-4.5 in yellow, SSP3-7.0 in red and SSP5-8.5 in dark red) ensemble means. Further details on data sources and processing are available in the chapter data table (Table 10.SM.11).

As noted in [[#10.6.4.4|Section 10.6.4.4]] , the Mediterranean summer climate is affected by large-scale circulation patterns, of which the summer NAO is the most important ( [[#Folland--2009|Folland et al., 2009]] ; [[#Bladé--2012|Bladé et al., 2012]] ). [[#Barcikowska--2020|Barcikowska et al. (2020)]] highlight the importance of correctly simulating the summer NAO impact on the Mediterranean climate, as it partly offsets the anthropogenic warming signal in the western and central Mediterranean.

Climate models project a reduction in precipitation in all seasons, and a northward and eastward expansion of the Mediterranean climate, with the affected areas becoming more arid with an increased summer drying (Atlas.8.5; [[#Alessandri--2015|Alessandri et al., 2015]] ; [[#Mariotti--2015|Mariotti et al., 2015]] ; [[#Rajczak--2017|Rajczak and Schär, 2017]] ; [[#Waha--2017|Waha et al., 2017]] ; [[#Barredo--2018|Barredo et al., 2018]] ; [[#Lionello--2018|Lionello and Scarascia, 2018]] ; [[#Spinoni--2018|Spinoni et al., 2018]] , 2020). The drying can contribute to the enhanced warming by land surface feedbacks ( [[#Whan--2015|Whan et al., 2015]] ; [[#Lorenz--2016|Lorenz et al., 2016]] ; [[#Russo--2019|Russo et al., 2019]] ). A negative feedback to this dryness-induced warming might be provided by an enhanced moisture transport into the dry area associated with the dynamical response of the atmosphere ( [[#Zhou--2021|]] [[#Zhou--2021|Zhou et al., 2021]] ). Due to the arid climate, no positive soil moisture-temperature feedback is found over the North African regions of the Mediterranean, where the surface energy budget is mostly governed by radiative cooling ( [[#Lelieveld--2016|Lelieveld et al., 2016]] ), implying that soil moisture feedbacks are not contributing to enhanced warming over those regions.

Over the Mediterranean region, daily maximum temperature is projected to increase more than the daily minimum. Consequently, the difference between daytime maxima and nighttime minima is expected to increase, particularly in summer ( [[#Lionello--2018|Lionello and Scarascia, 2018]] ). Temperature extremes will be affected as well, with a dramatic increase in the number of warm days and reduction of cold nights ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ; [[#Lionello--2020|Lionello and Scarascia, 2020]] ). The Mediterranean summer warming will also increase the frequency and intensity of heatwaves ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ).

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