Editing IPCC:AR6/WGI/Chapter-4 (section)

==== 4.6.1.1 Temperature ====

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Global warming of 1.5°C implies higher mean temperatures compared to 1850–1900, with generally higher warming over land compared to ocean areas ( ''virtuallycertain'' ) and larger warming in high latitudes compared to low latitudes (Figure 4.31). In addition, global warming of 2°C versus 1.5°C results in robust increases in the mean temperatures in almost all locations, both on land and in the ocean ( ''virtually certain'' ), with subsequent further warming at almost all locations at higher levels of global warming ( ''virtually certain'' ) ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). For each particular level of global warming, relatively larger mean warming is projected for land regions ( ''virtually certain'' ) (see Figure 4.31; [[#Christensen--2013|Christensen et al., 2013]] ; [[#Collins--2013|Collins et al., 2013]] ; [[#Seneviratne--2016|Seneviratne et al., 2016]] ). The projected changes at 1.5°C and 2°C global warming are consistent with observed historical global trends in temperature and their attribution to anthropogenic forcing (Chapter 3), as well as with observed changes under the recent global warming of 0.5°C ( [[#Schleussner--2017|Schleussner et al., 2017]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). That is, spatial patterns of temperature changes associated with the 0.5°C difference in GMST warming between 1991–2010 and 1960–1979 ( [[#Schleussner--2017|Schleussner et al., 2017]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ) are consistent with projected changes under 1.5°C and 2°C of global warming.

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[[File:68da52712f4289321d6b5d7412f0fcaf IPCC_AR6_WGI_Figure_4_31.png]]

'''Figure 4.31''' '''|''' '''Projected spatial patterns of change in annual average near-surface temperature (°C) at different levels of global warming.''' Displayed are '''(a–d)''' spatial patterns of change in annual average near-surface temperature at 1.5°C, 2°C, 3°C, and 4°C of global warming relative to the period 1850–1900 and '''(e–g)''' spatial patterns of differences in temperature change at 2°C, 3°C, and 4°C of global warming compared to 1.5°C of global warming. The number of models used is indicated in the top right of the maps. No overlay indicates regions where the change is robust and ''likely'' emerges from internal variability. That is, where at least 66% of the models show a change greater than the internal-variability threshold ( [[#4.2.6|Section 4.2.6]] ) and at least 80% of the models agree on the sign of change. Diagonal lines indicate regions with no change or no robust significant change, where fewer than 66% of the models show change greater than the internal-variability threshold. Crossed lines indicate areas of conflicting signals where at least 66% of the models show change greater than the internal-variability threshold but fewer than 80% of all models agree on the sign of change. Values were assessed from a 20-year period at a given warming level, based on model simulations under the Tier-1 SSPs of CMIP6. Further details on data sources and processing are available in the chapter data table (Table 4.SM.1).

The largest increase in annual mean temperature is found in the high latitudes of the Northern Hemisphere across all levels of global warming ( ''virtually certain'' ) (Figure 4.31). This phenomenon peaks in the Arctic and is known as Arctic amplification, with the underlying physical mechanisms assessed in detail in [[#4.5.1|Section 4.5.1]] and [[IPCC:Wg1:Chapter:Chapter-7|Chapter 7]] (Section 7.4.4.1). For the CMIP6 ensemble average considered here, Arctic annual mean temperatures warm by a factor of 2.3, 2.5, 2.4 and 2.4 for 1.5°C, 2°C, 3°C and 4°C of global warming, respectively. That is, Arctic warming scales approximately linearly with GSAT. Generally, when Arctic amplification is considered across individual models, warming occurs at a factor of two to four times the global level of warming. It is ''unlikely'' that warming in the Southern Hemisphere high latitudes in the 21st century will exceed the change in GSAT, or that it will substantially exceed warming in the tropics, for GSAT change ranging between 1.5°C and 4°C (Figure 4.31 and Table 4.2). Correspondingly, there is ''low confidence'' of Antarctic amplification occurring under transient, 21st century low mitigation scenarios (Table 4.2 and Section 7.4.4.1). The Antarctic continent is projected to warm at a higher rate than the mid-latitude Southern Ocean, however, at all levels of global warming (Figure 4.31). The relevant physical mechanisms that reduce the amplitude of polar amplification over Antarctica compared to the Arctic are assessed in detail in [[#4.5.1|Section 4.5.1]] and [[IPCC:Wg1:Chapter:Chapter-7|Chapter 7]] (Section 7.4.4.1). In the Southern Hemisphere the strongest warming over land is to occur, at any given level of global warming, over the subtropical areas of South America, southern Africa and Australia ( ''high confidence'' ). The relatively strong warming in subtropical southern Africa may be attributed to strong soil-moisture–temperature coupling and projected increased dryness under enhanced subsidence ( [[#Engelbrecht--2015|Engelbrecht et al., 2015]] ; [[#Vogel--2017|Vogel et al., 2017]] ). Across the globe, in the tropics, subtropics, and mid- to high latitudes, temperatures tend to scale linearly with the level of increase in GSAT and patterns of change are largely scenario independent ( ''high confidence'' ).

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