Editing IPCC:AR6/WGI/TS (section)

==== TS.4.3.2 Region-by-Region Changes in Climatic Impact-Drivers ====

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This section provides a continental synthesis of changes in CIDs, some examples of which are presented in Figure TS.25.

'''With 2°C global warming, and as early as the mid-21st century, a wide range of CIDs, particularly related to the water cycle and storms, are expected to show simultaneous region-specific changes relative to the recent past with ''high'' or ''medium confidence'' . In a number of regions (Southern Africa, the Mediterranean, North Central America, Western North America, the Amazon regions, South-Western South America, and Australia), increases in one or more of drought, aridity and fire weather ( ''high confidence'' ) will affect a wide range of sectors, including agriculture, forestry, health and ecosystems. In another group of regions (North-Western, Central and Eastern North America, Arctic regions, North-Western South America, Northern, Western and Central and Eastern Europe, Siberia, Central, South and East Asia, Southern Australia and New Zealand), decreases in snow and/or ice or increases in pluvial/river flooding ( ''high confidence'' ) will affect sectors such as winter tourism, energy production, river transportation and infrastructure. Links to chapters 11.9, 12.3, 12.4, 12.5, Table 12.2'''
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===== TS.4.3.2.1 Africa =====

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'''Additional regional changes in Africa, besides those described in Section TS.4.3.1, include a projected decrease in total precipitation in the northernmost and southernmost regions ( ''high confidence'' ), with Western Africa having a west-to-east pattern of decreasing-to-increasing precipitation ( ''medium confidence'' ). Increases in heavy precipitation that can lead to pluvial floods ( ''high confidence'' ) are projected for most African regions, even as increasing dry CIDs (aridity; hydrological, agricultural and ecological droughts; fire weather) are projected in the western part of Western Africa, Southern Africa and Northern Africa and the Mediterranean regions ( ''medium'' to ''high confidence'' ). Links to chapters 8.4, 11.3, 11.6, 11.9, 12.4, Atlas.4'''
In addition to the main changes summarized above and in Section TS.4.3.1, additional details per CID are given below.

'''Heat and cold:''' Observed and projected increases in mean temperature and a shift toward heat extreme characteristics are broadly similar to the generic pattern described in Section TS.4.3.1. Links to chapters 2.3.1.1.2, 11.3, 11.9, 12.4.1.1, Atlas.4.2, Atlas.4.4

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[[File:727e1fb83cd7f937f79ce8d9d92b8312 IPCC_AR6_WGI_TS_Figure_25.png]]

'''Figure TS.25 |''' '''Distribution of projected changes in selected climatic impact-driver (CID) indices for selected regions for Coupled Model Intercomparison Project Phases 5 and 6 (CMIP6, CMIP5) and Coordinated Regional Downscaling Experiment (CORDEX) model ensembles.''' ''The intent of this figure is to show that many CID projections for multiple global warming levels and scenarios time slices are available for all the AR6 WGI reference regions and are based on both global (CMIP5, CMIP6) and regional (CORDEX) model ensembles.'' Different indices are shown for different region: for Eastern Europe and North Asia, the mean number of days per year with maximum temperature exceeding 35°C; for Central America, the Caribbean, South West Asia, South Asia and South East Asia, the mean number of days per year with the National Oceanic and Atmospheric Administration (NOAA) Heat Index exceeding 41°C; for Australasia, East Asia and Russian Far East, the average shoreline position change; for South America, Europe and Africa, the mean change in 1-in-100-year river discharge per unit catchment area (m <sup>3</sup> s <sup>–1</sup> km <sup>–2</sup> ); and for North America, the median change in the number of days with snow water equivalent (SWE) over 100 mm. For each box plot, the changes or the climatological values are reported with respect to, or compared to, the recent past (1995–2014) period for 1.5°C, 2 <sup>°</sup> C and 4 <sup>°</sup> C global warming levels and for mid-century (2041–2060) or end-century (2081–2100) periods for the CMIP5 and CORDEX RCP8.5 and RCP2.6 and CMIP6 SSP5-8.5 and SSP1-2.6 scenarios ensembles. Links to chapters Figures 12.5, 12.6, 12.9, 12.SM.1, 12.SM.2, and 12.SM.6

'''Wet and dry:''' Mean precipitation changes have been observed over Africa, but the historical trends are not spatially coherent ( ''high confidence'' ). North Eastern Africa, East Southern Africa and Central Africa have experienced a decline in rainfall since about 1980 and parts of West Africa an increase ( ''high confidence'' ). Increases in the frequency and/or the intensity of heavy rainfall have been observed in East and West Southern Africa, and the eastern Mediterranean region ( ''medium confidence'' ). Increasing trends in river flood occurrence can be identified beyond 1980 in East and West Southern Africa ( ''medium confidence'' ) and Western Africa ( ''high confidence'' ). However, Northern Africa and West Southern Africa are ''likely'' to have a reduction in precipitation. Over West Africa, rainfall is projected to decrease in the western Sahel subregion and increase along the Guinea Coast subregion ( ''medium confidence'' ). Rainfall is projected to increase over Eastern Africa ( ''medium confidence'' ). Links to chapters 8.3.1.6, 11.4, 11.9, 12.4.1.2, Atlas.4.2, Atlas.4.4, Atlas.4.5

Precipitation declines and aridity trends in Western Africa, Central Africa, Southern Africa and the Mediterranean co-occur with trends towards increased agricultural and ecological droughts in the same regions ( ''medium confidence'' ). Trends towards increased hydrological droughts have been observed in the Mediterranean ( ''high confidence'' ) and Western Africa ( ''medium confidence'' ). These trends correspond with projected regional increases in aridity and fire weather conditions ( ''high confidence'' ). Links to chapters 8.3.1.6, 8.4.1.6, 11.6, 11.9, 12.4.1.2

'''Wind:''' Mean wind, extreme winds and the wind energy potential in North Africa and the Mediterranean are projected to decrease across all scenarios ( ''high confidence'' ). Over Western Africa and Southern Africa, a future significant increase in wind speed and wind energy potential is projected ( ''medium confidence'' ). There is a projected decrease in the frequency of tropical cyclones making landfall over Madagascar, East Southern Africa and East Africa ( ''medium confidence'' ). Links to chapters 12.4.1.3

'''Snow and ice:''' There is ''high confidence'' that African glaciers and snow have very significantly decreased in the last decades and that this trend will continue in the 21st century. Links to chapters 12.4.1.4

'''Coastal and oceanic:''' Relative sea level has increased at a higher rate than GMSL around Africa over the last 3 decades. The present day 1-in-100-year extreme total water level (ETWL) is between 0.1 m and 1.2 m around Africa, with values around 1 m or above along the East and West Southern and Central Eastern Africa coasts. Satellite-derived shoreline retreat rates up to 1 m yr <sup>–1</sup> have been observed around the continent from 1984 to 2015, except in South Eastern Africa, which has experienced a shoreline progradation (growth) rate of 0.1 m yr <sup>–1</sup> over the same period. Links to chapters 12.4.1.5

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===== TS.4.3.2.2 Asia =====

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Due to the high climatological and geographical heterogeneity of Asia, some assessment findings below are summarized over five sub-continental areas comprising one or more of the AR6 WGI reference regions (Box TS.12): East Asia (EAS+ECA), North Asia (WSB+ESB+RFE), South Asia (SAS), South East Asia (SEA) and South West Asia (ARP+WCA).

'''Additional regional changes in Asia, besides those features described in Section TS.4.3.1, include historical trends of annual precipitation that show considerable regional differences ( ''high confidence'' ). East Asian Monsoon precipitation has changed, with drying in the north and wetting in the south since the 1950s, and annual mean precipitation totals ''very likely'' have increased over most territories of North Asia since the mid-1970s ( ''high confidence'' ). South Asian summer monsoon precipitation decreased over several areas since the mid-20th century ( ''high confidence'' ) but is ''likely'' to increase during the 21st century, with enhanced interannual variability. (Box TS.13)''' '''Increases in precipitation and river floods are projected over much of Asia: in the annual mean precipitation in East, North, South and South East Asia ( ''high confidence'' ); for extremes in East, South, West Central, North and South East Asia ( ''high confidence'' ) and Arabian Peninsula ( ''medium confidence'' ); and for river floods in East, South and South East Asia and East Siberia ( ''medium confidence'' ). Aridity in East and West Central Asia is projected to increase, especially beyond the middle of the 21st century and global warming levels beyond 2°C ( ''medium confidence'' ). Fire weather seasons are projected to lengthen and intensify everywhere except South East Asia, Tibetan Plateau and Arabian Peninsula ( ''medium confidence'' ).''' '''Surface wind speeds have been decreasing in Asia ( high confidence ), but there is a large uncertainty in future trends, with medium confidence that mean wind speeds will decrease in North Asia, East Asia and Tibetan Plateau and that tropical cyclones will have decreasing frequency and increasing intensity overall in South East and East Asia.''' '''Over North Asia, increases in permafrost temperature and its thawing have been observed over recent decades ( ''high confidence'' ). Future projections indicate continuing decline in seasonal snow duration, glacial mass, and permafrost area by mid-century ( ''high confidence'' ). Snow-covered areas and snow volumes will decrease in most regions of the Hindu Kush Himalaya (HKH) during the 21st century, and snowline elevations will rise ( ''high confidence'' ) and glacier volumes are ''likely'' to decline with greater mass loss in higher CO <sub>2</sub> emissions scenarios. Heavy snowfall is increasing in East Asia and North Asia ( ''medium confidence'' ) but with limited evidence on future changes in hail and snow avalanches.''' '''Links to chapters 2.3, 8.3, 8.4, 9.5, 9.6, 10.6, Box 10.4, 11.4, 11.5, 11.7, 11.9, 12.4.2, Atlas.3.1, Atlas.5, Atlas.5.2, Atlas.5.3, Atlas.5.4, Atlas.5.5'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' Over all regions of Asia, observed and projected increases in mean temperature and a shift toward heat extreme characteristics are broadly similar to the generic pattern described in Section TS.4.3.1. Over South East Asia, annual mean surface temperature will ''likely'' increase by a slightly smaller amount than the global average. Links to chapters Atlas.5.4.4

'''Wet and dry:''' Over East Asia, historical trends of annual precipitation show considerable regional differences but with increases over north-west China and South Korea ( ''high confidence'' ). Daily precipitation extremes have increased over part of the region ( ''high confidence'' ). Extreme hydrological drought frequency has increased in a region extending from south-west to north-east China, with projected increases of agricultural and ecological drought for 4°C GWL and fire weather for 2°C and above ( ''medium confidence'' ) ''.'' Links to chapters 8.3.2, 8.4.2, 11.4.4, 11.4.5, 11.9, 12.4.2.2, Atlas.5.1.2

Over North Asia, annual mean precipitation totals have ''very likely'' increased, causing more intense flooding events, and there is ''medium confidence'' that the number of dry days has decreased. Concurrently, total soil moisture is projected to decline extensively ( ''medium confidence'' ). Links to chapters 8.3.1.3, 8.4.1.6, 11.4.5, 11.5.2, 11.5.5, 12.4.2.2, Atlas.5.2.2

Over South Asia, the summer monsoon precipitation decreased over several areas since the mid-20th century ( ''high confidence'' ), while it increased in parts of the western HKH and decreased over eastern-central HKH ( ''medium confidence'' ). The frequency of heavy precipitation and flood events has increased over several areas during the last few decades ( ''medium confidence'' ). Links to chapters 8.3.1.3, 8.3.2.4.1, 8.4.1.5, 8.4.2.4.1, 10.6.3.3, 10.6.3.5, 10.6.3.6, 10.6.3.8, Cross-Chapter Box 10.4, 11.4.1, 11.4.2, 11.4.5, 11.5.5, 12.4.2.2, Box 10.4, [[IPCC:Wg1:Chapter:Atlas|Atlas]] 5.3.2

Over South East Asia, mean precipitation trends are not spatially coherent or consistent across datasets and seasons ( ''high confidence'' ). Most of the region has experienced an increase in rainfall intensity but with a reduced number of wet days ( ''medium confidence'' ). Rainfall is projected to increase in the northern parts of South East Asia and decrease in areas in the Maritime Continent ( ''medium confidence'' ). Links to chapters 8.4.1, 11.4.2, 11.5.5, 11.9, 12.4.2.2, Atlas.3.1, Atlas.5.4.2, Atlas.5.4.4

Over South West Asia, an observed annual precipitation decline over the Arabian Peninsula since the 1980s of 6.3 mm per decade is contrasted with observed increases between 1.3 mm and 4.8 mm per decade during 1960–2013 over the elevated part of eastern West Central Asia ( ''very high confidence'' ), along with an increase of the frequency and intensity of extreme precipitation. Links to chapters Figure 8.19, Figure 8.20, 8.3.1.6, 8.4.1.6, 11.9, Table 11.2A, 12.4.2.2, Atlas.5.5

'''Wind:''' Over East Asia, the terrestrial near-surface wind speed has decreased and is projected to decrease further in the future ( ''medium confidence'' ). Since the mid 1980’s, there has been an increase in the number and intensification rate of intense TCs ( ''medium confidence'' ), with a significant north-westward shift in tracks and a northward shift in their average latitude, increasing exposure over East China, the Korean Peninsula and the Japanese Archipelago ( ''medium confidence'' ). Links to chapters 11.7.1, 12.4.2.3

Over North Asia, there is ''medium confidence'' for a decreasing trend in wind speed during 1979–2018 and for projected continuing decreases of terrestrial near-surface wind speed. Links to chapters 2.3.1.4.4, 12.4.2.3

Over South East Asia, although there is no significant long-term trend in the number of TCs, fewer but more extreme TCs have affected the Philippines during 1951–2013. Links to chapters 11.7.4, 12.4.2.3

'''Snow and ice:''' Over East Asia, decreases have been observed in the frequency, and increases in the mean intensity, of snowfall in north-western, north-eastern and south-eastern China and the eastern Tibetan Plateau since the 1960s. Heavy snowfall is projected to occur more frequently in some parts of Japan ( ''medium confidence'' ). Links to chapters 12.4.2.4, Atlas.5.1.2

Over North Asia, seasonal snow duration and extent have decreased in recent decades ( ''high confidence'' ), and maximum snow depth ''likely'' has increased since the mid-1970s, particularly over the south of the Russian Far East. Links to chapters 2.3.2.5, 8.3.1.7.2, 9.5, 12.4.2.4, Atlas.5.2, Atlas.5.4

Over South Asia, snow cover has reduced over most of the HKH since the early 21st century, and glaciers have thinned, retreated, and lost mass since the 1970s ( ''high confidence'' ), although the Karakoram glaciers have either slightly gained mass or are in an approximately balanced state ( ''medium confidence'' ). Links to chapters 8.3.1.7.1, Cross-Chapter Box 10.4

Over South West Asia, mountain permafrost degradation at high altitudes has increased the instability of mountain slopes in the past decade ( ''medium confidence'' ). More than 60% of glacier mass in the Caucasus is projected to disappear under RCP8.5 emissions by the end of the 21st century ( ''medium confidence'' ). Links to chapters 9.5.1, 9.5.3, 12.4.2.4

'''Coastal and oceanic:''' Over the last three decades, relative sea level has increased at a rate higher than GMSL around Asia ( ''high confidence'' ). Gross coastal area loss and shoreline retreat has been observed over 1984–2015, but with localized shoreline progradation in the Russian Far East, East and South East Asia. Links to chapters 12.4.2.5

Projections show that regional mean sea level continues to rise ( ''high confidence'' ), ranging from 0.4–0.5 m under SSP1-2.6 to 0.8–1.0 m under SSP5-8.5 for 2081–2100 relative to 1995–2014 (median values). This will contribute to more frequent coastal flooding and higher ETWL in low-lying areas and coastal erosion along sandy beaches ( ''high confidence'' ). There is ''high confidence'' that compound effects of climate change, land subsidence, and human factors will lead to higher flood levels and prolonged inundation in the Mekong Delta and other Asian coasts. Links to chapters 9.6.1, 9.6.3, 12.4.2.5

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===== TS.4.3.2.3 Australasia =====

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'''Additional regional changes in Australasia, besides those features described in Section TS.4.3.1, include a significant decrease in April to October rainfall in the south-west of the state of Western Australia, observed from 1910 to 2019 and attributable to human influence ( ''high confidence'' ), which is ''very likely'' to continue in future. Agricultural and ecological droughts and hydrological droughts have increased over Southern Australia ( ''medium confidence'' ), and meteorological droughts have decreased over Northern and Central Australia ( ''medium confidence'' ). Relative sea level has increased over the period 1993–2018 at a rate higher than GMSL around Australasia ( ''high confidence'' ). Sandy shorelines have retreated around the region, except in Southern Australia, where a shoreline progradation rate of 0.1 m yr <sup>–1</sup> has been observed.''' '''In the future, heavy precipitation and pluvial flooding are ''very likely'' to increase over Northern Australia and Central Australia, and they are ''likely'' to increase elsewhere in Australasia for global warming levels (GWLs) exceeding 2°C and with ''medium confidence'' for a 2°C GWL. Agricultural and ecological droughts are projected to increase in Southern and Eastern Australia ( ''medium confidence'' ) for a 2°C GWL. Fire weather is projected to increase throughout Australia ( ''high confidence'' ) and New Zealand ( ''medium confidence'' ). Snowfall is expected to decrease throughout the region at high altitudes in both Australia ( ''high confidence'' ) and New Zealand ( ''medium confidence'' ), with glaciers receding in New Zealand ( ''high confidence'' ). Links to chapters 11.4, Table 11.6, 12.3, 12.4.3, Atlas.6.4, Atlas.6.5'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' Observed and projected increases in mean temperature and a shift toward heat extreme characteristics are broadly similar to the generic pattern described in Section TS.4.3.1. Links to chapters 11.9, 12.4.3.1, Atlas.6

'''Wet and dry:''' There is ''medium confidence'' that heavy precipitation has increased in Northern Australia since 1950. Annual mean precipitation is projected to increase in the south and west of New Zealand ( ''medium confidence'' ) and is projected to decrease in south-west Southern Australia ( ''high confidence'' ), Eastern Australia ( ''medium confidence'' ), and in the north and east of New Zealand ( ''medium confidence'' ) for a GWL of 2°C. There is ''medium confidence'' that river flooding will increase in New Zealand and Australia, with higher increases in Northern Australia. Aridity is projected to increase with ''medium confidence'' in Southern Australia ( ''high confidence'' in south-west Southern Australia), Eastern Australia ( ''medium confidence'' ) and in the north and east of New Zealand ( ''medium confidence'' ) for GWLs around 2°C. Links to chapters 11.4, 11.9, Table 11.6, 12.4.3.2, Atlas.6.2

'''Wind:''' Mean wind speeds are projected to increase in parts of north-eastern Australia ( ''medium confidence'' ) by the end of the 21st century under high CO <sub>2</sub> emissions scenarios. TCs in north-eastern and north Australia are projected to decrease in number ( ''high confidence'' ) but increase in intensity except for ‘east coast lows’ ( ''low confidence'' ). Links to chapters 12.4.3.3

'''Snow and ice:''' Observations in Australia show that the snow season length has decreased by 5% in the last five decades. Furthermore, the date of peak snowfall in Australia has advanced by 11 days over the last 5 decades. Glacier ice volume in New Zealand has decreased by 33% from 1977 to 2018. Links to chapters 12.4.3.4, Atlas.6.2

'''Coastal and oceanic:''' Observed changes in marine heatwaves (MHWs) over the 20th century in the region show an increase in their occurrence frequency, except along the south-east coast of New Zealand, an increase in duration per event, and the total number of MHW days per decade, with the change being stronger in the Tasman Sea than elsewhere. The present day 1-in-100-year ETWL is between 0.5–2.5 m around most of Australia, except the north-western coast where 1-in-100-year ETWL can be as high as 6–7 m. Links to chapters Box 9.1, 12.3.1.5, 12.4.3.5

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===== TS.4.3.2.4 Central and South America =====

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'''Additional regional changes in Central and South America, besides those features described in Section TS.4.3.1, include increases in mean and extreme precipitation in South-Eastern South America since the 1960s ( ''high confidence'' ) (Section TS.4.2.3). Decreasing trends in mean precipitation and increasing trends in agricultural and ecological drought are observed over North-Eastern South America ( ''medium confidence'' ). The intensity and frequency of extreme precipitation and pluvial floods is projected to increase over South-Eastern South America, Southern South America, Northern South America, South American Monsoon and North-Eastern South America ( ''medium confidence'' ) for a 2°C GWL and above. Increases of agricultural and ecological drought are projected in South America Monsoon and Southern South America, and fire weather is projected to increase over several regions (Northern South America, the South American Monsoon, North-Eastern South America and South-Western South America) ( ''high confidence'' ). Links to chapters 8.3, 8.4, 11.3, 11.4, 11.9, Table 11.13, Table 11.14, Table 11.15, 12.4.4.2, Atlas.7.1, Atlas.7.2'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' Observed and projected increases in mean temperature and a shift toward heat extreme characteristics are broadly similar to the generic pattern described in Section TS.4.3.1. Links to chapters 11.3.2, 11.3.5, Table 11.13, 12.4.4.1, Atlas.7.1.2, Atlas.7.2.2, Atlas.7.2.4

'''Wet and dry:''' Mean precipitation is projected to change in a dipole pattern with increases in North-Western and South-Eastern South America and decreases in North-Eastern and South-Western South America ( ''high confidence'' ) and with further decreases in Northern South America and Southern Central America ( ''medium confidence'' ). In Northern South America and Southern Central America, aridity and agricultural and ecological droughts are increasing with ''medium confidence'' . Fire weather is projected to increase over Southern Central America and Southern South America with ''medium confidence'' . Links to chapters 8.3.1.3, 8.4.2.4.5, 11.4.2, 11.9, Table 11.14, Table 11.15, 12.4.4.2, Atlas.7.2.2, Atlas.7.2.4

'''Wind:''' Climate projections indicate an increase in mean wind speed and in wind power potential over the Amazonian region (Northern South America, South American Monsoon, North-Eastern South America) ( ''medium confidence'' ). Links to chapters 12.4.4.3

'''Snow and ice:''' Glacier volume loss and permafrost thawing will ''likely'' continue in the Andes Cordillera under all climate scenarios, causing important reductions in river flow and potentially high-magnitude glacial lake outburst floods. Links to chapters 9.5.1.1, 12.4.4.4

'''Coastal and oceanic:''' Around Central and South America, relative sea level has increased at a higher rate than GMSL in the South Atlantic and the subtropical North Atlantic, and at a rate lower than GMSL in the East Pacific over the last 3 decades. The present day 1-in-100-year ETWL is highest in Southern and South-Western South America subregions, where it can be as large as 5 to 6 m. Satellite observations for 1984–2015 show shoreline retreat rates along the sandy coasts of Southern Central America, South-Eastern South America and Southern South America, while shoreline progradation rates have been observed in North-Western South America and Northern South America. Over the period 1982–2016, the coastlines experienced at least one MHW per year, and more along the Pacific coast of North Central America and the Atlantic coast of South-Eastern South America. Links to chapters 12.4.4.5

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===== TS.4.3.2.5 Europe =====

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'''Additional regional changes in Europe, besides those features described in Section TS.4.3.1, include observed increases in pluvial flooding in Northern Europe and hydrological and agricultural/ecological droughts in the Mediterranean ( ''high confidence'' ), which have been attributed to human influence with ''high'' and ''medium confidence'' , respectively. Increased mean precipitation amounts at high latitudes in boreal winter and reduced summer precipitation in southern Europe are projected starting from a 2°C GWL ( ''high confidence'' ). Aridity, agricultural and hydrological droughts and fire weather conditions will increase in the Mediterranean region starting from 2°C GWL ( ''high confidence'' ). Pluvial flooding will increase everywhere with ''high confidence'' except for ''medium confidence'' in the Mediterranean; in Western and Central Europe this also applies to river flooding starting from a 2°C GWL ( ''high confidence'' ). Most periglacial processes in Northern Europe are projected to disappear by the end of the 21st century, even for a low warming scenario ( ''medium confidence'' ). Links to chapters 8.3, 11.3, 11.9, 12.4.5, 12.5.2, Atlas.8.2, Atlas.8.4'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' Observed and projected increases in mean temperature and a shift toward heat extreme characteristics are broadly similar to the generic pattern described in Section TS.4.3.1. Links to chapters 11.3, 11.9, 12.4.5.1, 12.5.2, Atlas.8.2, Atlas.8.4

'''Wet and dry:''' There is ''medium confidence'' that annual mean precipitation has increased in Northern Europe, West and Central Europe, and Eastern Europe since the early 20th century and ''high confidence'' for increases in extreme precipitation. In the European Mediterranean, the magnitude and sign of observed land precipitation trends depend on time period and exact study region ( ''medium confidence'' ). There is ''medium confidence'' that river floods will decrease in Northern, Eastern and southern Europe for high warming levels. Links to chapters 8.3.1.3, 11.3, 11.9, 12.4.5.2, Atlas.8.2, Atlas.8.4

'''Wind:''' Mean wind speed over land has decreased ( ''medium confidence'' ), but the role of human-induced climate change has not been established. There is ''high confidence'' that mean wind speeds will decrease in Mediterranean areas and ''medium confidence'' for such decreases in Northern Europe for GWLs exceeding 2°C. The frequency of Medicanes (tropical-like cyclones in the Mediterranean) is projected to decrease ( ''medium confidence'' ). Links to chapters 11.9, 12.4.5.3

'''Snow and ice:''' In the Alps, snow cover will decrease below elevations of 1500–2000 m throughout the 21st century ( ''high confidence'' ). A reduction of glacier ice volume is projected in the European Alps and Scandinavia with ''high confidence'' and with ''medium confidence'' for the timing and mass change rates. Links to chapters 9.5.2, 12.4.5.4

'''Coastal and oceanic:''' Over the last three decades, relative sea level has increased at a lower rate than GMSL in the sub-polar North Atlantic coasts of Europe. The present-day 1-in-100-year ETWL is between 0.5–1.5 m in the Mediterranean basin and 2.5–5.0 m in the western Atlantic European coasts, around the United Kingdom and along the North Sea coast, and lower at 1.5–2.5 m along the Baltic Sea coast. Satellite-derived shoreline change estimates over 1984–2015 indicate shoreline retreat rates of around 0.5 m yr <sup>–1</sup> along the sandy coasts of Central Europe and the Mediterranean and more or less stable shorelines in Northern Europe. Over the period 1982–2016, the coastlines of Europe experienced on average more than 2.0 MHW per year, with the eastern Mediterranean and Scandinavia experiencing 2.5–3 MHWs per year. Links to chapters 12.4.5.5

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===== TS.4.3.2.6 North America =====

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'''Additional regional changes in North America, besides those features described in Section TS.4.3.1, include changes in North American wet and dry CIDs, which are largely organized by the north-east (more wet) to south-west (more dry) pattern of mean precipitation change, although heavy precipitation increases are widespread ( ''high confidence'' ). Increasing evaporative demand will expand agricultural and ecological drought and fire weather (particularly in summertime) in Central North America, Western North America and Northern Central America (from ''medium'' to ''high confidence'' ). Severe wind storms, tropical cyclones and dust storms in North America are shifting toward more extreme characteristics ( ''medium confidence'' ), and both observations and projections point to strong changes in the seasonal and geographic range of snow and ice conditions in the coming decades ( ''very high confidence'' ). General findings for relative sea level, coastal flooding and erosion will not apply for areas with substantial land uplift around the Hudson Bay and Southern Alaska. Links to chapters 8.4, 11.4, 11.5, 11.7, 11.9, 12.4, Atlas.9.4'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' Observed and projected increases in mean temperature and a shift toward heat extreme characteristics are broadly similar to the generic pattern described in Section TS.4.3.1. Links to chapters 11.3, 11.9, 12.4.6.1, Atlas.9.2, Atlas.9.4

'''Wet and dry:''' Annual precipitation increased over parts of Eastern and Central North America during 1960–2015 ( ''high confidence'' ) and has decreased in parts of south-western United States and north-western Mexico ( ''medium confidence'' ). River floods are projected to increase for all North American regions other than Northern Central America (med ''ium confidence'' ). Links to chapters 8.4.2.4, 11.4, 11.5, 11.9, 12.4.6.2, Atlas.9.2, Atlas.9.4

Agricultural and ecological drought increases have been observed in Western North America ( ''medium confidence'' ), and aridity is projected to increase in the south-western United States and Northern Central America, with lower summer soil moisture across much of the continental interior ( ''medium confidence'' ). Links to chapters 8.4.1, 11.6.2, 12.4.6.2

'''Wind:''' Projections indicate a greater number of the most intense TCs, with slower translation speeds and higher rainfall potential for Mexico’s Pacific Coast, the Gulf Coast and the United States East Coast ( ''medium confidence'' ). Mean wind speed and wind power potential are projected to decrease in Western North America ( ''high confidence'' ), with differences between global and regional models lending ''low confidence'' elsewhere. Links to chapters 11.4, 11.7, 12.4.6.3

'''Snow and ice:''' It is ''likely'' that some high-latitude regions will experience an increase in winter snow water equivalent due to the snowfall increase prevailing over the warming trend. At sustained GWLs between 3°C and 5°C, nearly all glacial mass in Western Canada and Western North America will disappear ( ''medium confidence'' ). Links to chapters 9.5.1, 9.5.3, 12.4.6.4, Atlas.9.4

'''Coastal and oceanic:''' Around North America, relative sea level has increased over the last three decades at a rate lower than GMSL in the subpolar North Atlantic and in the East Pacific, while it has increased at a rate higher than GMSL in the subtropical North Atlantic. Observations indicate that episodic coastal flooding is increasing along many coastlines in North America. Shoreline retreat rates of around 1 m yr <sup>–1</sup> have been observed during 1984–2015 along the sandy coasts of North-Western North America and Northern Central America, while portions of the United States Gulf Coast have seen a retreat rate approaching 2.5 m yr <sup>–1</sup> . Sandy shorelines along Eastern North America and Western North America have remained more or less stable during 1984–2014, but a shoreline progradation rate of around 0.5 m yr <sup>–1</sup> has been observed in North-Eastern North America. Links to chapters 12.4.6.5

<div id="TS.4.3.2.7" class="h4-container"></div>

<span id="ts.4.3.2.7-small-islands"></span>
===== TS.4.3.2.7 Small Islands =====

<div id="h4-8-siblings" class="h4-siblings"></div>

'''Additional regional changes in Small Islands, besides those features described in Section TS.4.3.1, include a ''likely'' decrease in rainfall during boreal summer in the Caribbean and in some parts of the Pacific islands poleward of 20° latitude in both the Northern and Southern Hemispheres. These drying trends will ''likely'' continue in coming decades. Fewer but more intense tropical cyclones are projected starting from a 2°C GWL ( ''medium confidence'' ). Links to chapters 9.6, 11.3, 11.4, 11.7, 11.9, 12.4.7, Atlas.10.2, Atlas.10.4, Cross-Chapter Box Atlas.2'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' It is ''very likely'' that most Small Islands have warmed over the period of instrumental records, and continued temperature increases in the 21st century will further increase heat stress in these regions. Links to chapters 11.3.2, 11.9, 12.4.7.1, Atlas.10.2, Atlas.10.4, Cross-Chapter Box Atlas.2

'''Wet and dry:''' Observed and projected rainfall trends vary spatially across the Small Islands. Higher evapotranspiration under a warming climate can partially offset future increases or amplify future reductions in rainfall, resulting in increased aridity as well as more severe agricultural and ecological drought in the Caribbean ( ''medium confidence'' ). Links to chapters 11.4.2, 11.9, 12.4.7.2, Atlas.10.2, Atlas.10.4, Cross-Chapter Box Atlas.2

'''Wind:''' Global changes indicate that Small Islands will face fewer but more intense TCs, with spatial inconsistency in projections given poleward shifts in TC tracks ( ''medium confidence'' ). Links to chapters 11.7.1.2, 11.7.1.5, 12.4.7.3

'''Coastal and oceanic:''' Continued relative sea level rise is ''very likely'' in the ocean around Small Islands and, along with storm surges and waves, will exacerbate coastal inundation with the potential to increase saltwater intrusion into aquifers in small islands. Shoreline retreat is projected along sandy coasts of most small islands ( ''high confidence'' ). Links to chapters 9.6.3.3, 12.4.7.4, Cross-Chapter Box Atlas.2

<div id="TS.4.3.2.8" class="h4-container"></div>

<span id="ts.4.3.2.8-polar"></span>

===== TS.4.3.2.8 Polar =====

<div id="h4-9-siblings" class="h4-siblings"></div>

'''It is ''virtually certain'' that surface warming in the Arctic will continue to be more pronounced than the global average warming over the 21st century. An intensification of the polar water cycle will increase mean precipitation, with precipitation intensity becoming stronger and more ''likely'' to be rainfall rather than snowfall ( ''high confidence'' ). Permafrost warming, loss of seasonal snow cover, and glacier melt will be widespread ( ''high confidence'' ). There is ''high confidence'' that both the Greenland and Antarctic ice sheets have lost mass since 1992 and will continue to lose mass throughout this century under all emissions scenarios. Relative sea level and coastal flooding are projected to increase in areas other than regions with substantial land uplift ( ''medium confidence'' ). Links to chapters 2.3, 3.4, 4.3, 4.5, 7.4, 8.2, 8.4, Box 8.2, 9.5, 12.4.9, Atlas.11.1, Atlas.11.2'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Heat and cold:''' Changes in Antarctica showed larger spatial variability, with ''very likely'' warming in the Antarctic Peninsula since the 1950s and no overall trend in East Antarctica. Less warming and weaker polar amplification are projected as ''very likely'' over the Antarctic than in the Arctic, with a weak polar amplification projected as ''very likely'' by the end of the 21st century. Links to chapters 4.3.1, 4.5.1, 7.4.4, 12.4.9.1, Atlas.11.1, Atlas.11.2

'''Wet and dry:''' Recent decades have seen a general decrease in Arctic aridity ( ''high confidence'' ), with increased moisture transport leading to higher precipitation, humidity and streamflow and a corresponding decrease in dry days. Antarctic precipitation showed a positive trend during the 20th century. The water cycle is projected to intensify in both polar regions, leading to higher precipitation totals (and a shift to more heavy precipitation) and higher fraction of precipitation falling as rain. In the Arctic, this will result in higher river flood potential and earlier meltwater flooding, altering seasonal characteristics of flooding ( ''high confidence'' ). A lengthening of the fire season ( ''medium confidence'' ) and encroachment of fire regimes into tundra regions ( ''high confidence'' ) are projected. Links to chapters 8.2.3, 8.4.1, Box 8.2, 9.4.1, 9.4.2, 12.4.9.2, Atlas.11.1, Atlas.11.2

'''Wind:''' There is ''medium confidence'' in mean wind decrease over the Russian Arctic and Arctic North-East North America, but ''low confidence'' of changes in other Arctic regions and Antarctica. Links to chapters 12.4.9.3

'''Snow and ice:''' Reductions in spring snow cover extent have occurred across the Northern Hemisphere since at least 1978 ( ''very high confidence'' ). Permafrost warming and thawing have been widespread in the Arctic since the 1980s ( ''high confidence'' ), causing strong heterogeneity in surface conditions. There is ''high confidence'' in future glacier- and ice-sheet loss, permafrost warming, decreasing permafrost extent and decreasing seasonal duration and extent of snow cover in the Arctic. Decline in seasonal sea ice coverage along the majority of the Arctic coastline in recent decades is projected to continue, contributing to an increase in coastal hazards (including open water storm surge, coastal erosion and flooding). Links to chapters 2.3.2, 3.4.2, 3.4.3, 9.4.1, 9.4.2, 9.5, 12.4.6, 12.4.9, Atlas.11.2

'''Coastal and oceanic:''' Higher sea levels contribute to ''high confidence'' for projected increases of Arctic coastal flooding and higher coastal erosion (aided by sea ice loss) ( ''medium confidence'' ), with lower confidence for those regions with substantial land uplift (Arctic North-East North America and Greenland). Links to chapters 12.4.9.5

<div id="TS.4.3.2.9" class="h4-container"></div>

<span id="ts.4.3.2.9-ocean"></span>

===== TS.4.3.2.9 Ocean =====

<div id="h4-9-siblings" class="h4-siblings"></div>

'''The Indian Ocean, western equatorial Pacific Ocean and western boundary currents have warmed faster than the global average ( ''very high confidence'' ), with the largest changes in the frequency of marine heatwaves (MHWs) projected in the western tropical Pacific and the Arctic Ocean ( ''medium confidence'' ). The Pacific and Southern Ocean are projected to freshen and the Atlantic to become more saline ( ''medium confidence'' ). Anthropogenic warming is ''very likely'' to further decrease ocean oxygen concentrations, and this deoxygenation is expected to persist for thousands of years ( ''medium confidence'' ). Arctic sea ice losses are projected to continue, leading to a practically ice-free Arctic in September by the end of the 21st century under high CO <sub>2</sub> emissions scenarios ( ''high confidence'' ). Links to chapters 2.3, 5.3, 9.2, 9.3, Box 9.2, 12.3.6, 12.4.8'''
In addition to the main changes summarized above and in Section TS.4.3.1, further details are given below.

'''Ocean surface temperature:''' The Southern Ocean, the eastern equatorial Pacific, and the North Atlantic Ocean have warmed more slowly than the global average or slightly cooled. Global warming of 2°C above 1850–1900 levels would result in the exceedance of numerous hazard thresholds for pathogens, seagrasses, mangroves, kelp forests, rocky shores, coral reefs and other marine ecosystems ( ''medium confidence'' ). Links to chapters 9.2.13, 12.4.8

'''Marine heatwaves:''' Moderate increases in MHW frequency are projected for mid-latitudes, and only small increases are projected for the Southern Ocean ( ''medium confidence'' ). Under the SSP5-8.5 scenario, permanent MHWs (more than 360 days per year) are projected to occur in the 21st century in parts of the tropical ocean, the Arctic Ocean, and around 45°S; however, the occurrence of such permanent MHWs can be largely avoided under the SSP1-2.6 scenario. Links to chapters Box 9.2, 12.4.8

'''Ocean acidity:''' With the rising CO <sub>2</sub> concentration, the ocean surface pH has declined globally over the past four decades ( ''virtually certain'' ). Links to chapters 2.3.3.5, 5.3.3.2, 12.4.8

'''Ocean salinity:''' At the basin scale, it is ''very likely'' that the Pacific and the Southern Ocean have freshened while the Atlantic has become more saline. Links to chapters 2.3.3.2, 9.2.2.2, 12.4.8

'''Dissolved oxygen:''' In recent decades, low oxygen zones in ocean ecosystems have expanded. Links to chapters 2.3.4.2, 5.3.3.2, 12.4.8

'''Sea ice:''' Arctic perennial sea ice is being replaced by thin, seasonal ice, with earlier spring melt and delayed fall freeze up. There is no clear trend in the Antarctic sea ice area over the past few decades and ''low confidence'' in its future change. Links to chapters 2.3.2.1.1, 9.3.1.1, 12.4.8, 12.4.9

<div id="TS.4.3.2.10" class="h4-container"></div>

<span id="ts.4.3.2.10-other-typological-domains"></span>

===== TS.4.3.2.10 Other Typological Domains =====

<div id="h4-10-siblings" class="h4-siblings"></div>

'''Some types of regions found in different continents face common climate challenges regardless of their location. These include biodiversity hot spots that will ''very likely'' see even more extreme heat and droughts, mountain areas where a projected raising in the freezing level height will alter snow and ice conditions ( ''high confidence'' ), and tropical forests that are increasingly prone to fire weather ( ''medium confidence'' ). Links to chapters 8.4, Box 8.2, 9.5, 12.3, 12.4'''
Biodiversity hotspots located around the world will each face unique challenges in CID changes. Heat, drought and length of dry season, wildfire weather, sea surface temperature and deoxygenation are relevant drivers to terrestrial and freshwater ecosystems and have marked increasing trends. Links to chapters 12.3, 12.4.10.1

Desert and semi-arid areas are strongly affected by CIDs such as extreme heat, drought and dust storms, with large-scale aridity trends contributing to expanding drylands in some regions ( ''high confidence'' ). Links to chapters 12.3, 12.4.10.3

Average warming in mountain areas varies with elevation, but the pattern is not globally uniform ( ''medium confidence'' ). Extreme precipitation is projected to increase in major mountainous regions ( ''medium'' to ''high confidence'' depending on location), with potential cascading consequences of floods, landslides and lake outbursts in all scenarios ( ''medium confidence'' ). Links to chapters 8.4.1.5, Box 8.2, 9.5.1.3, 9.5.3.3, 9.5.2.3, Cross-Chapter Box 10.4, 11.5.5, 12.3, 12.4.1–12.4.6, 12.4.10.4

Most tropical forests are challenged by a mix of emerging warming trends that are particularly large in comparison to historical variability ( ''medium confidence'' ). Water cycle changes bring prolonged drought, longer dry seasons and increased fire weather to many tropical forests ( ''medium confidence'' ). Links to chapters 10.5, 12.3, 12.4

<div id="box-ts.14" class="h2-container box-container"></div>

'''Box TS.14 | Urban Areas'''

<div id="h2-35-siblings" class="h2-siblings"></div>

'''With global warming, urban areas and cities will be affected by more frequent occurrences of extreme climate events, such as heatwaves, with more hot days and warm nights as well as sea level rise and increases in tropical cyclone storm surge and rainfall intensity that will increase the probability of coastal city flooding ( ''high confidence'' ). Links to chapters Box 10.3, 11.3, 11.5, 12.3, 12.4'''
Urban areas have special interactions with the climate system, for instance in terms of heat islands and altering the water cycle, and thereby will be more affected by extreme climate events such as extreme heat ( ''high confidence'' ). With global warming, increasing relative sea level compounded by increasing tropical cyclone storm surge and rainfall intensity will increase the probability of coastal city flooding ( ''high confidence'' ). Arctic coastal settlements are particularly exposed to climate change due to sea ice retreat ( ''high confidence'' ). Improvements in urban climate modelling and climate monitoring networks have contributed to understanding the mutual interaction between regional and urban climate ( ''high confidence'' ). Links to chapters Box 10.3, 11.3, 11.5, 12.3, 12.4

Despite having a negligible effect on global surface temperature ( ''high confidence'' ), urbanization has exacerbated the effects of global warming through its contribution to the observed warming trend in and near cities, particularly in annual mean minimum temperature ( ''very high confidence'' ) and increases in mean and extreme precipitation over and downwind of the city, especially in the afternoon and early evening ( ''medium confidence'' ). Links to chapters 2.3, Box 10.3, 11.3, 11.4, 12.3, 12.4

Combining climate change projections with urban growth scenarios, future urbanization will amplify ( ''very high confidence'' ) the projected local air temperature increase, particularly by strong influence on minimum temperatures, which is approximately comparable in magnitude to global warming ( ''high confidence'' ). Compared to present day, large implications are expected from the combination of future urban development and more frequent occurrence of extreme climate events, such as heatwaves, with more hot days and warm nights adding to heat stress in cities ( ''very high confidence'' ). Links to chapters Box 10.2, 11.3, 12.4

Both sea levels and air temperatures are projected to rise in most coastal settlements ( ''high confidence'' ). There is ''high confidence'' in an increase in pluvial flood potential in urban areas where extreme precipitation is projected to increase, especially at high global warming levels. Links to chapters 11.4, 11.5, 12.4

-----

<div id="footnote-020" class="_idFootnote"></div>

[[#footnote-020-backlink|1]] In this Technical Summary, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium, or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high, and very high, and typeset in italics, e.g., ''medium confidence'' . For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see Chapter 1, Box 1.1 for more details).

<div id="footnote-019" class="_idFootnote"></div>

[[#footnote-019-backlink|2]] In this Technical Summary, the following terms are used to indicate the assessed likelihood of an outcome or a result: virtually certain 99–100% probability, very likely 90–100%, likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely likely : 95–100%, more likely than not &gt;50–100%, and extremely unlikely 0–5%) may also be used when appropriate. Assessed likelihood is typeset in italics, e.g., ''very likely'' (see Chapter 1, Box 1.1 for more details). Throughout the WGI report and unless stated otherwise, uncertainty is quantified using 90% uncertainty intervals. The 90% uncertainty interval, reported in square brackets [x to y], is estimated to have a 90% likelihood of covering the value that is being estimated. The range encompasses the median value, and there is an estimated 10% combined likelihood of the value being below the lower end of the range (x) and above its upper end (y). Often, the distribution will be considered symmetric about the corresponding best estimate, but this is not always the case. In this Report, an assessed 90% uncertainty interval is referred to as a ‘ ''very likely'' range’. Similarly, an assessed 66% uncertainty interval is referred to as a ‘ ''likely'' range’.

<div id="footnote-018" class="_idFootnote"></div>

[[#footnote-018-backlink|3]] The regional traceback matrices that provide the location of the assessment findings synthesized in Section TS.4 are in the Supplementary Material (SM) of Chapter 10.

<div id="footnote-017" class="_idFootnote"></div>

[[#footnote-017-backlink|4]] Data archive is available at https://catalogue.ceda.ac.uk/uuid/3234e9111d4f4354af00c3aaecd879b7 .

<div id="footnote-016" class="_idFootnote"></div>

[[#footnote-016-backlink|5]] https://interactive-atlas.ipcc.ch/

<div id="footnote-015" class="_idFootnote"></div>

[[#footnote-015-backlink|6]] The AR6 figures use one of the following approaches. For observations, the absence of ‘x’ symbols shows areas with statistical significance, while the presence of ‘x’ indicates non-significance. For model projections, the method offers two approaches with varying complexity. In the simple approach, ''high agreement'' (≥80%) is indicated with no overlay, and diagonal lines (///) show ''low agreement'' (&lt;80%); In the advanced approach, areas with no overlay display robust signal (≥66% of models show change greater than the variability threshold and ≥80% of all models agree on the sign of change), reverse diagonal lines () show no robust signal, and crossed lines show conflicting signals (i.e., significant change but ''low agreement'' ). Cross-Chapter Box Atlas.1 provides more information on the AR6 method for visualizing robustness and uncertainty on maps.

<div id="footnote-014" class="_idFootnote"></div>

[[#footnote-014-backlink|7]] Although not a core concept of the WGI Report, deep uncertainty is used in the Technical Summary in the following sense: ‘A situation of deep uncertainty exists when experts or stakeholders do not know or cannot agree on: (1) appropriate conceptual models that describe relationships among key driving forces in a system; (2) the probability distributions used to represent uncertainty about key variables and parameters; and/or (3) how to weigh and value desirable alternative outcomes’ (Lempert et al., 2003). Lempert, R. J., Popper, S. W., and Bankes, S. C. (2003). ''Shaping the next one hundred years: New methods for quantitative long-term strategy analysis (MR-1626-RPC)'' . Santa Monica, CA: The RAND Pardee Center.

<div id="footnote-013" class="_idFootnote"></div>

[[#footnote-013-backlink|8]] The assessment covers scientific literature accepted for publication by 31 January 2021.

<div id="footnote-012" class="_idFootnote"></div>

[[#footnote-012-backlink|9]] Human influence on the climate system refers to human-driven activities that lead to changes in the climate system due to perturbations of Earth’s energy budget (also called anthropogenic forcing). Human influence results from emissions of greenhouse gases, aerosols and tropospheric ozone precursors, ozone-depleting substances, and land-use change.

<div id="footnote-011" class="_idFootnote"></div>

[[#footnote-011-backlink|10]] Throughout this Technical Summary, ‘main driver’ means responsible for more than 50% of the change.

<div id="footnote-010" class="_idFootnote"></div>

[[#footnote-010-backlink|11]] Throughout the WGI report and unless stated otherwise, uncertainty is quantified using 90% uncertainty intervals. The 90% uncertainty interval, reported in square brackets [x to y], is estimated to have a 90% likelihood of covering the value that is being estimated. The range encompasses the median value and there is an estimated 10% combined likelihood of the value being below the lower end of the range (x) and above its upper end (y). Often the distribution will be considered symmetric about the corresponding best estimate, but this is not always the case. In this Report, an assessed 90% uncertainty interval is referred to as a ‘ ''very likely'' range’. Similarly, an assessed 66% uncertainty interval is referred to as a ‘ ''likely'' range’.

<div id="footnote-009" class="_idFootnote"></div>

[[#footnote-009-backlink|12]] Increased stratification reduces the vertical exchange of heat, salinity, oxygen, carbon and nutrients. Stratification is an important indicator for ocean circulation.

<div id="footnote-008" class="_idFootnote"></div>

[[#footnote-008-backlink|13]] Several baselines or reference periods are used consistently throughout this Report. Baseline refers to a period against which anomalies (i.e., differences from the average value for the baseline period) are calculated. Examples include the 1750 baseline (used for anthropogenic radiative forcings), the 1850–1900 baseline (an approximation for pre-industrial global surface temperature from which global warming levels are calculated) and the 1995–2014 baseline (used for many climate model projections). A reference period indicates a time period over which various statistics are calculated (e.g., the near-term reference period, 2021–2040). Paleo reference periods are listed in Box TS.2. Links to chapters 1.4.1, Cross-Chapter Boxes 1.2 and 2.1

<div id="footnote-007" class="_idFootnote"></div>

[[#footnote-007-backlink|14]] Please refer to Section TS.1.3.1 for an overview of the climate change scenarios used in this Report.

<div id="footnote-006" class="_idFootnote"></div>

[[#footnote-006-backlink|15]] In this Report, equilibrium climate sensitivity is defined as the equilibrium (steady state) change in the surface temperature following a doubling of the atmospheric carbon dioxide (CO 2 ) concentration from pre-industrial conditions.

<div id="footnote-005" class="_idFootnote"></div>

[[#footnote-005-backlink|16]] In this Report, transient climate response is defined as the surface temperature response for the hypothetical scenario in which atmospheric carbon dioxide (CO 2 ) increases at 1% yr <sup>–1</sup> from pre-industrial to the time of a doubling of atmospheric CO 2 concentration.

<div id="footnote-004" class="_idFootnote"></div>

[[#footnote-004-backlink|17]] Throughout this Report, scenarios are referred to as SSPx-y, where “SSPx” refers to the Shared Socio-economic Pathway or “SSP” describing the socio-economic trends underlying the scenario, and “y” refers to the approximate target level of radiative forcing (in W m <sup>–-2</sup> ) resulting from the scenario in the year 2100.

<div id="footnote-003" class="_idFootnote"></div>

[[#footnote-003-backlink|18]] The transient surface temperature change per unit of cumulative CO 2 emissions, usually 1000 GtC.

<div id="footnote-002" class="_idFootnote"></div>

[[#footnote-002-backlink|19]] Throughout this Technical Summary, ‘main driver’ means responsible for more than 50% of the change.

<div id="footnote-001" class="_idFootnote"></div>

[[#footnote-001-backlink|20]] For reference, the Planck temperature response for a doubling of atmospheric CO 2 is approximately 1.2°C at equilibrium.

<div id="footnote-000" class="_idFootnote"></div>

[[#footnote-000-backlink|21]] Although cirrus cloud thinning aims to cool the planet by increasing longwave emissions to space, it is included in the portfolio of SRM options for consistency with AR5 and SR1.5. Links to chapters 4.6.3.3