Editing IPCC:AR6/WGI/Chapter-11 (section)

=== Temperature Extremes ===

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'''The frequency and intensity of hot extremes (including heatwaves) have increased, and those of cold extremes have decreased on the global scale since 1950''' ( ''virtually certain'' '''). This also applies at regional scale, with more than 80% of AR6 regions''' [[#footnote-011|1]] '''showing similar changes assessed to be at least''' ''likely'' '''.''' In a few regions, ''limited evidence'' (data or literature) prevents the reliable estimation of trends. {11.3, 11.9}

'''Human-induced greenhouse gas forcing is the main driver of the observed changes in hot and cold extremes on the global scale''' ( ''virtually certain'' ''') and on most continents''' ( ''very likely'' ''').''' The effect of enhanced greenhouse gas concentrations on extreme temperatures is moderated or amplified at the regional scale by regional processes such as soil moisture or snow/ice-albedo feedbacks, by regional forcing from land-use and land-cover changes, or aerosol concentrations, and decadal and multi-decadal natural variability. Changes in anthropogenic aerosol concentrations have ''likely'' affected trends in hot extremes in some regions. Irrigation and crop expansion have attenuated increases in summer hot extremes in some regions, such as the Midwestern USA ( ''medium confidence'' ). Urbanization has ''likely'' exacerbated changes in temperature extremes in cities, in particular for nighttime extremes. {11.1, 11.2, 11.3}

'''The frequency and intensity of hot extremes will continue to increase and those of cold extremes will continue to decrease, at global and continental scales and in nearly all inhabited regions''' <sup>1</sup> '''with increasing global warming levels.''' This will be the case even if global warming is stabilized at 1.5°C. Relative to present-day conditions, changes in the intensity of extremes would be at least double at 2°C, and quadruple at 3°C of global warming, compared to changes at 1.5°C of global warming. The number of hot days and hot nights and the length, frequency, and/or intensity of warm spells or heatwaves will increase over most land areas ( ''virtually certain'' ). In most regions, future changes in the intensity of temperature extremes will ''very likely'' be proportional to changes in global warming, and up to two to three times larger ( ''high confidence'' ). The highest increase of temperature of hottest days is projected in some mid-latitude and semi-arid regions and in the South American Monsoon region, at about 1.5 times to twice the rate of global warming ( ''high confidence'' ). The highest increase of temperature of coldest days is projected in Arctic regions, at about three times the rate of global warming ( ''high confidence'' ). The frequency of hot temperature extreme events will ''very likely'' increase nonlinearly with increasing global warming, with larger percentage increases for rarer events. {11.2, 11.3, 11.9; Table 11.1; Figure 11.3}

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