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

=== Atlas.8.1 Key Features of the Regional Climate and Findings From Previous IPCC Assessments ===

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==== Atlas.8.1.1 Key Features of the Regional Climate ====

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Westerly winds and the accompanying Atlantic storm track with cyclones and anticyclones travelling from the Atlantic towards inland Europe are the main climatic features that characterize daily to interannual variability in the European region. The Siberian High in winter determines cold weather in Eastern Europe and can affect other regions with cold outbreaks. Intra-seasonal and interannual variations are driven by modes of climate variability such as the North Atlantic Oscillation (NAO; Table Atlas.1 and Annex IV.2). Global warming can lead to systematic changes in regional climate variability via thermodynamic responses such as altered lapse rates ( [[#Kröner--2017|Kröner et al., 2017]] ; [[#Brogli--2019|Brogli et al., 2019]] ) and land-atmosphere feedbacks ( [[#Zampieri--2011|Zampieri and Lionello, 2011]] ; [[#Boé--2014|Boé and Terray, 2014]] ). Regional feedbacks involving the land-sea contrast, sea surface, land surface, clouds, aerosols, radiation and other processes modulate the regional response to enhanced warming.

Four climatic regions are defined for Europe (Figure Atlas.24). The Mediterranean region (MED) in the south is characterized by mild winters and hot and dry summers (Mediterranean climate; [[IPCC:Wg1:Chapter:Chapter-10#10.6.4.2|Section 10.6.4.2]] ). It covers both Europe and Africa, and MED assessments in this section generally imply the entire MED domain unless stated otherwise. The Western and Central Europe region (WCE) has distinct summer and winter seasons with increasing continentality of climate eastwards. The Northern Europe region (NEU), close to the Atlantic Ocean, is characterized by high humidity and relatively mild winters, and strong exposure to the Atlantic storm track. Eastern Europe (EEU) covers the western part of Russia and neighbouring territories and has continental characteristics. Many regional datasets and model projections assessed here do not sufficiently cover the EEU region.

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==== Atlas.8.1.2 Findings From Previous IPCC Assessments ====

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The AR5 WGII ( [[#Kovats--2014|Kovats et al., 2014]] ) reports with ''high confidence'' that observed climate trends show regionally varying changes in temperature and rainfall in Europe. The average temperature in Europe has continued to increase, with seasonally different rates of warming being greatest in high latitudes in Northern Europe. Annual precipitation has increased in Northern Europe and decreased in parts of Southern Europe. The SROCC ( [[#Hock--2019b|Hock et al., 2019b]] ) reports with ''high confidence'' that a reduction in snow cover at low elevation and glacier extent is observed in recent decades, with consequent changes in annual and seasonal runoff patterns. According to the SRCCL report ( [[#IPCC--2019b|IPCC, 2019b]] ) there is ''high agreement'' that observed vegetation greening and forestation in the last 30 years cools summer surface temperature and warms winter temperature due to decreased snow cover and increased snow shading in forested areas. It is ''very likely'' that aerosol column amounts have declined over Europe since the mid-1980s.

The AR5 ( [[#Collins--2013|Collins et al., 2013]] ) reports that the ability of models to simulate the climate in Europe has improved in many important aspects. Particularly relevant for this region are increased model resolution and a better representation of the land surface processes in many of the models that participated in CMIP5. The spread in climate model projections is still substantial, partly due to pronounced internal variability in this region (particularly NAO and AMO). In the winter half year, NEU and WCE are ''likely'' to have increased mean precipitation associated with increased atmospheric moisture and moisture convergence, and intensification in extratropical cyclone activity. No change or a moderate reduction is projected for MED. In the summer half year, it is ''likely'' that NEU and WCE mean precipitation will have only small changes with a notable reduction in MED. According to SR1.5 ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ), these precipitation changes are more pronounced at 2°C than at 1.5°C of global warming. For a 2°C global warming level, an increase in runoff is projected for north-eastern Europe while decreases are projected in the Mediterranean region, where runoff differences between 1.5°C and 2°C global warming will be most prominent ( ''medium confidence'' ). According to SROCC ( [[#Hock--2019b|Hock et al., 2019b]] ) the RCP8.5 projections lead to a loss of more than 80% of the ice mass from small glaciers by the end of century in Central Europe ( ''high confidence'' ). Snow cover and glaciers are projected to decrease throughout the 21st century.

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