Editing IPCC:AR6/WGI/TS (section)

== Box TS.13 | Monsoons ==

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'''Global land monsoon precipitation decreased from the 1950s to the 1980s, partly due to anthropogenic aerosols, but has increased since then in response to GHG forcing and large-scale multi-decadal variability (''medium confidence''). Northern Hemispheric anthropogenic aerosols weakened the regional monsoon circulations in South Asia, East Asia and West Africa during the second half of the 20th century, thereby offsetting the expected strengthening of monsoon precipitation in response to GHG-induced warming (''high confidence'').'''

'''During the 21st century, global land monsoon precipitation is projected to increase in response to GHG warming in all time horizons and scenarios (''high confidence''). Over South and South East Asia, East Asia and the central Sahel, monsoon precipitation is projected to increase, whereas over North America and the far western Sahel it is projected to decrease (''medium confidence''). There is ''low confidence'' in projected precipitation changes in the South American and Australian-Maritime Continent monsoons. At global and regional scales, near-term monsoon changes will be dominated by the effects of internal variability (''medium confidence''). Links to chapters 2.3, Cross-Chapter Box 2.4, 3.3, 4.4, 4.5, 8.2, 8.3, 8.4, 8.5, Box 8.1, Box 8.2, 10.6'''

'''Global Monsoon'''

Paleoclimate records indicate that during warm climates, like the mid-Pliocene Warm Period, monsoon systems were stronger (''medium confidence''). In the instrumental records, global summer monsoon precipitation intensity has ''likely'' increased since the 1980s, dominated by Northern Hemisphere summer trends and large multi-decadal variability. Contrary to the expected increase of precipitation under global warming, the Northern Hemisphere monsoon regions experienced declining precipitation from the 1950s to 1980s, which is partly attributable to the influence of anthropogenic aerosols (''medium confidence'') (Box TS.13, Figure 1). Links to chapters 2.3.1, Cross-Chapter Box 2.4, 3.3.2, 3.3.3

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'''Box TS.13, Figure 1 |'''

'''Global and regional monsoons: past trends and projected changes.''' ''The intent of this figure is to show changes in precipitation over regional monsoon domains in terms of observed past trends, how greenhouse gases and aerosols relate to these changes, and in terms of future projections in one intermediate emissions scenario in the near, medium and long term.'' (a) Global (black contour) and regional monsoons (colour shaded) domains. The global monsoon (''GM'') is defined as the area with local summer-minus-winter precipitation rate exceeding 2.5 mm day <sup>–1</sup> (see Annex V). The regional monsoon domains are defined based on published literature and expert judgement (see Annex V) and accounting for the fact that the climatological summer monsoon rainy season varies across the individual regions. Assessed regional monsoons are South and South East Asia (''SAsiaM, Jun–July–August–September''), East Asia (''EAsiaM, June–July–August''), West Africa (''WAfriM, June–July–August–September'') '','' North America (''NAmerM, July–August–-September''), South America (''SAmerM, December–January–February''), Australia and Maritime Continent Monsoon (''AusMCM, December–January–February''). Equatorial South America (''EqSAmer'') and South Africa (''SAfri'') regions are also shown, as they receive unimodal summer seasonal rainfall although their qualification as monsoons is subject to discussion. (b) Global and regional monsoons precipitation trends based on DAMIP CMIP6 simulations with both natural and anthropogenic (ALL), greenhouse gas only (GHG), aerosols only (AER) and natural only (NAT) radiative forcing. Weighted ensemble means are based on nine Coupled model Intercomparison Project Phase 6 (CMIP6) models contributing to the MIP (with at least three members). Observed trends computed from CRU, GPCP and APHRO (only for ''SAsiaM'' and ''EAsiaM'') datasets are shown as well. (c) Percentage change in projected seasonal mean precipitation over global and regional monsoons domain in the near term (2021–2040), mid-term (2041–2060), and long term (2081–2100) under SSP2-4.5 based on 24 CMIP6 models. Links to chapters Figures 8.11 and 8.22

With continued global warming, it is ''likely'' that global land monsoon precipitation will increase during this century (Box TS.13, Figure 1), particularly in the Northern Hemisphere, although the monsoon circulation is projected to weaken. A slowdown of the tropical circulation with global warming can partly offset the warming-induced strengthening of precipitation in monsoon regions (''high confidence''). In the near term, global monsoon changes are ''likely'' to be dominated by the effects of internal variability and model uncertainties (''medium confidence''). In the long term, global monsoon rainfall change will feature a robust north–south asymmetry characterized by a greater increase in the Northern Hemisphere than in the Southern Hemisphere and an east–west asymmetry characterized by enhanced Asian–African monsoons and a weakened North American monsoon (''medium confidence''). Links to chapters 4.4.1, 4.5.1, 8.4.1

'''Regional Monsoons'''

Paleoclimate reconstructions indicate stronger monsoons in the Northern Hemisphere but weaker ones in the Southern Hemisphere during warm periods, particularly for the South and South East Asian, East Asian, and North and South American monsoons, with the opposite occurring during cold periods (''medium confidence''). It is ''very likely'' that Northern Hemispheric anthropogenic aerosols weakened the regional monsoon circulations in South Asia, East Asia and West Africa during the second half of the 20th century, thereby offsetting the expected strengthening of monsoon precipitation in response to GHG-induced warming (Box TS.13, Figure 1). Multiple lines of evidence explain this contrast over South Asia, with the observed trends dominated by the effects of aerosols, while future projections are mostly driven by GHG increases. The recent partial recovery and enhanced intensity of monsoon precipitation over West Africa is related to the growing influence of GHGs with an additional contribution due to the reduced cooling effect of anthropogenic aerosols, emitted largely from North America and Europe (''medium confidence''). For other regional monsoons, that is, North and South America and Australia, there is ''low confidence'' in the attribution of recent changes in precipitation (Box TS.13, Figure 1) and winds. Links to chapters 2.3.1, 8.3.1, 8.3.2, Box 8.1, 10.6.3

Projections of regional monsoons during the 21st century indicate contrasting (region-dependent) and uncertain precipitation and circulation changes. The annual contrast between the wettest and driest month of the year is ''likely'' to increase by 3–5% per degree Celsius in most monsoon regions in terms of precipitation, precipitation minus evaporation, and runoff (''medium confidence''). For the North American monsoon, projections indicate a decrease in precipitation, whereas increased monsoon rainfall is projected over South and South East Asia and over East Asia (''medium confidence'') (Box TS.13, Figure 1). West African monsoon precipitation is projected to increase over the central Sahel and decrease over the far western Sahel (''medium confidence''). There is ''low confidence'' in projected precipitation changes in the South American and Australian-Maritime Continent regional monsoons (for both magnitude and sign) (Box TS.13, Figure 1). There is ''medium confidence'' that the monsoon season will be delayed in the Sahel and ''high confidence'' that it will be delayed in North and South America. Links to chapters 8.2.2, 8.4.2.4, Box 8.2

'''Building the Assessment from Multiple Lines of Evidence'''

Large natural variability of monsoon precipitation across different time scales, found in both paleoclimate reconstructions and instrumental measurements, poses an inherent challenge for robust quantification of future changes in precipitation at regional and smaller spatial scales. At both global and regional scales, there is ''medium confidence'' that internal variability contributes the largest uncertainty related to projected changes, at least in the near term (2021–2040). A collapse of the Atlantic Meridional Overturning Circulation could weaken the African and Asian monsoons but strengthen the Southern Hemisphere monsoons (''high confidence''). Links to chapters 4.4.4, 4.5.1, Cross-Chapter Box 4.1, 8.5.2, 8.6.1, 9.2.3, 10.6.3

Overall, long-term (2081–2100) future changes in regional monsoons like the South and South East Asian monsoon are generally consistent across global (including high-resolution) and regional climate models and are supported by theoretical arguments. Uncertainties in simulating the observed characteristics of regional monsoon precipitation are related to varying complexities of regional monsoon processes and their responses to external forcing, internal variability, and deficiencies in representing monsoon warm rain processes, organized tropical convection, heavy orographic rainfall and cloud–aerosol interactions. Links to chapters 8.3.2, 8.5.1, 10.3.3, 10.6.3
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=== TS.4.3 Regional Climate Change and Implications for Climate Extremes and Climatic Impact-Drivers ===

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'''Current climate in all regions is already distinct from the climate of the early or mid-20th century with respect to several climatic impact-drivers (CIDs), resulting in shifting magnitude, frequency, duration, seasonality and spatial extent of associated climate indices (''high confidence''). It is ''very likely'' that mean temperatures have increased in all land regions and will continue to increase at rates greater than the global average (''high confidence''). The frequency of heat and cold extremes have increased and decreased, respectively. These changes are attributed to human influence in almost all regions (''medium'' to ''high confidence'') and will continue through the 21st century (''high confidence''). In particular, extreme heat would exceed critical thresholds for health, agriculture and other sectors more frequently by the mid 21st century with 2°C of global warming (''high confidence'').'''

'''Relative sea level rise is ''very likely'' to ''virtually certain'' (depending on the region) to continue during the 21st century, contributing to increased coastal flooding in low-lying areas (''high confidence'') and coastal erosion along most sandy coasts (''high confidence''). Sea level will continue to rise beyond 2100 (''high confidence'') (Box TS.4).'''

'''Every region of the world will experience concurrent changes in multiple CIDs by mid-century or at 2°C global warming and above (''high confidence''). Even for the current climate, climate change-induced shifts in CID distributions and event probabilities, some of which have occurred over recent decades, are relevant for risk assessments. Links to chapters 11.9, 12.1, 12.2, 12.4, 12.5, Atlas.3–Atlas.11'''

An overview of changes in regional CIDs (introduced in Section TS.1) is given in Table TS.5, which summarizes multiple lines of evidence on regional climate change derived from observed trends, attribution of these trends and future projections. The level of confidence and the amplitude in the projected direction of change in CIDs at a given time horizon depends on climate change mitigation efforts over the 21st century. It is evident from Table TS.5 that many heat, cold, snow and ice, coastal, and oceanic CID changes are projected with ''high confidence'' in most regions starting from a global warming level (GWL) of 2°C, indicating worldwide challenges. Changes in many other regional CIDs have higher confidence later in the 21st century or at higher GWLs (''high confidence''), and another small subset are projected with ''high confidence'' for the 1.5°C GWL. This section focuses on the 2°C GWL and mid-century time period because the signal emerges from natural variability for a wider range of CIDs at this higher warming level. Figure TS.22 shows the geographical location of regions belonging to one of five groups characterized by a specific combination of changing CIDs. The Regional Synthesis component of the Interactive [[IPCC:Wg1:Chapter:Atlas|Atlas]] provides comprehensive synthesis information about changes in all of the individual CIDs across all of the AR6 WGI reference regions. Links to chapters 10.5, Cross-Chapter Box 10.3, 11.1, 11.9, Box 11.1, 12.1, 12.2, 12.4, 12.5

'''Table TS.5 | Summary of confidence for climatic impact-driver changes in each AR6 WGI reference region (illustrated in Figure TS.25) across multiple lines of evidence for observed, attributed and projected directional changes.''' The colours represent their projected aggregate characteristic changes for the mid-21st century, considering scenarios RCP4.5, SSP2-4.5, SRES A1B, or above (RCP6.0, RCP8.5, SSP3-7.0, SSP5-8.5, SRES A2), which approximately encompasses global warming levels of 2.0°C to 2.4°C. Arrows indicate ''medium'' to ''high confidence'' trends derived from observations, and asterisks indicate ''medium'' and ''high confidence'' in attribution of observed changes. (North Africa is not an AR6 WGI reference region, but assessment here is based upon the African portion of the Mediterranean reference region). Links to chapters Tables 12.3–12.11 and Tables 11.4–11.21

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'''Notes:'''

'''Africa (projections)'''

1. Contrasted regional signal: drying in western portions and wetting in eastern portions

2. ''Likely'' increase over the Ethiopian Highlands

3. ''Medium confidence'' of decrease in frequency and increase in intensity

4. Along sandy coasts and in the absence of sufficient sediment supply from terrestrial or offshore sources

5. Substantial parts of the East Southern Africa and Madagascar coast are projected to prograde if present-day ambient shoreline change rates continue

'''Asia (projections)'''

1. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat.

2. Substantial parts of the coasts in these regions are projected to prograde if present-day ambient shoreline change rates continue

3. Tropical cyclones decrease in number but increase in intensity

4. ''High confidence'' of decrease in Indonesia (Atlas.5.4.5)

5. ''Medium confidence'' of decreasing in summer and increasing in winter

'''Australasia (projections)'''

1. ''High confidence'' of decrease in the south-west of the state of Western Australia

2. ''Medium confidence'' of decrease in north and east and increase in south and west

3. ''High confidence'' of increase in the south-west of the state of Western Australia

4. ''Medium confidence'' of increase in the north and east and decrease in south and west

5. ''Low confidence'' of increasing intensity, and ''high confidence'' of decreasing occurrence

6. ''High confidence'' of decrease in glacier volume, ''medium confidence'' of decrease in snow

7. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat

'''Central and South America (projections)'''

1. Increase in extreme flow in the Amazon basin

2. Tropical cyclones decrease in number but increase in intensity

3. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat.

4. Substantial parts of the North-Western South America, Northern South America and North-Eastern South America coasts are projected to prograde if present-day ambient shoreline change rates continue

'''Europe (projections)'''

1. Excluding southern United Kingdom

2. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat

3. The Baltic Sea shoreline is projected prograde if present-day ambient shoreline change rates continue.

4. For the Alps, conditions conducive to landslides are expected to increase

5. ''Low confidence'' of decrease in the southernmost part of the region

6. General decrease except in Aegean Sea

7. ''Medium confidence'' of decrease in frequency and increase in intensities

8. Except in the Northern Baltic Sea region

'''North America (projections)'''

1. Snow may increase in some high elevations and during the cold season and decrease in other seasons and at lower elevations

2. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat.

3. Increasing in northern regions and decreasing toward the south

4. Decreasing in northern regions and increasing toward the south

5. Higher confidence in northern regions and lower toward the south

6. Higher confidence in southern regions and lower toward the north

7. Higher confidence in increase for some climatic impact-driver indices during summertime

8. Increase in convective conditions but decrease in winter extratropical cyclones

9. Relative sea level rise reduced given land uplift in Southern Alaska

'''Small Islands (projections)'''

1. ''Very high confidence'' in the direction of change, but ''low'' to ''medium confidence'' in the magnitude of change due to model uncertainty

2. Decrease in eastern Pacific and southern Pacific subtropics, but increase in parts of western and equatorial Pacific; with seasonal variation in future changes

3. ''High confidence'' in increase in extreme rain frequency and intensity in western tropical Pacific; ''low confidence'' in magnitude of change due to model bias

4. Increase in southern Pacific

5. Increase in intensity; decrease in frequency except over central North Pacific.

6. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat.

'''Polar Terrestrial Regions (projections)'''

1. Snow may increase in some high elevations and during the cold season and decrease in other seasons and at lower elevations

2. ''Higher confidence'' in southern regions and lower toward the north

3. ''Higher confidence'' in increase for some climatic impact-driver indices during summertime

4. Glaciers decline even as some regional snow climatic impact-driver indices increase

5. Decreasing in west and increasing in east

6. Except for Northern Baltic Sea coasts where relative sea levels fall

7. Along sandy coasts and in the absence of additional sediment sinks/sources or any physical barriers to shoreline retreat

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'''Figure TS.22 |''' '''Synthesis of the geographical distribution of climatic impact-drivers changes and the number of AR6 WGI reference regions where they are projected to change.'''

'''Panel (a)''' shows the geographical location of regions belonging to one of five groups characterized by a specific combination of changing climatic impact-drivers (CIDs). The five groups are represented by the five different colours, and the CID combinations associated with each group are represented in the corresponding ‘fingerprint’ and text below the map. Each fingerprint comprises a set of CIDs projected to change with ''high confidence'' in every region in the group and a second set of CIDs, one or more of which are projected to change in each region with ''high'' or ''medium confidence'' . The CID combinations follow a progression from those becoming hotter and drier (group 1) to those becoming hotter and wetter (group 5). In between (groups 2–4), the CIDs that change include some becoming drier and some wetter and always include a set of CIDs which are getting hotter. Tropical cyclones and severe wind CID changes are represented on the map with black dots in the regions affected. Regions affected by coastal CID changes are described by text on the map. The five groups are chosen to provide a reasonable level of detail for each region while not overwhelming the map with a full summary of all aspects of the assessment, which is available in Table TS.5 and can be visualized in the Regional Synthesis component of the Interactive Atlas. The CID changes summarized in the figure represent ''high'' and ''medium confidence'' changes for the mid-21st century, considering scenarios SSP2-4.5, RCP4.5, SRES A1B, or above (SSP3-7.0, SSP5-8.5, RCP6.0, RCP8.5, SRES A2), which approximately encompasses global warming levels of 2.0°C to 2.4°C.

The bar chart in '''panel''' '''(b)''' shows the numbers of regions where each CID is increasing or decreasing with ''medium'' or ''high confidence'' for all land regions and ocean regions listed in Table TS.5. The colours represent the direction of change and the level of confidence in the change: purple indicates an increase while brown indicates a decrease; darker and lighter shades refer to ''high'' and ''medium confidence'' , respectively. Lighter background colours represent the maximum number of regions for which each CID is broadly relevant. Sub-panel (i) shows the 30 CIDs relevant to the land and coastal regions while sub-panel (ii) shows the 5 CIDs relevant to the open ocean regions. Marine heatwaves and ocean acidity are assessed for coastal ocean regions in panel (i) and for open ocean regions in panel (ii). Changes refer to a 20- to 30-year period centred around 2050 and/or consistent with 2°C global warming compared to a similar period within 1960–2014, except for hydrological drought and agricultural and ecological drought, which is compared to 1850–1900. Definitions of the regions are provided in Atlas.1, the Interactive [[IPCC:Wg1:Chapter:Atlas|Atlas]] (https://interactive-atlas.ipcc.ch/) and Chapter 12. (Table TS.5, Figure TS.24) Links to chapters 11.9, 12.2, 12.4, Atlas.1

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==== TS.4.3.1 Common Regional Changes in Climatic Impact-Drivers ====

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'''Heat and cold:''' Changes in temperature-related CIDs such as mean temperatures, growing season length, and extreme heat and frost have already occurred (''high confidence''), and many of these changes have been attributed to human activities (''medium confidence''). Over all land regions with sufficient data (i.e., all except Antarctica), observed changes in temperature have already clearly emerged outside the range of internal variability, relative to 1850–1900 (Figure TS.23). In tropical regions, recent past temperature distributions have already shifted to a range different to that of the early 20th century (''high confidence'') (Section TS.1.2.4). Most land areas have ''very likely'' warmed by at least 0.1°C per decade since 1960, and faster in recent decades. On regional-to-continental scales, trends of increased frequency of hot extremes and decreased frequency of cold extremes are generally consistent with the global-scale trends in mean temperature (''high confidence''). In a few regions, trends are difficult to assess due to limited data availability. Links to chapters 2.3.1.1, 11.3, 11.9, 12.4, Atlas.3.1

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'''Figure TS.23 |''' '''Time period during which the signals of temperature change in observed data aggregated over the reference regions emerged from the noise of annual variability in the respective aggregated data, using a signal-to-noise ratio of two as the threshold for emergence.''' ''The intent of this figure is to show, for the AR6 WGI reference regions, when a signal of annual mean surface temperature change emerged from the noise of annual variability in two global datasets and thus also provide some information on observational uncertainty.'' Emergence time is calculated for two global observational datasets: (a) Berkeley Earth and (b) CRUTEM5. Regions in the CRUTEM5 map are shaded grey when data are available over less than 50% of the area of the region. (Section TS.1.2.4) Links to chapters Figure Atlas.11

Warming trends observed in recent decades are projected to continue over the 21st century and over most land regions at a rate higher than the global average (''high confidence''). For given global warming levels, model projections from CMIP6 show future regional warming changes that are similar to those projected by CMIP5. However, projected regional warming in CMIP6 for given time periods and emissions scenarios has a wider range with a higher upper limit compared to CMIP5 because of the higher climate sensitivity in some CMIP6 models and differences in the forcings. Links to chapters Atlas.3–Atlas.11

Under RCP8.5/SSP5-8.5, it is ''likely'' that most land areas will experience further warming of at least 4°C compared to a 1995–2014 baseline by the end of the 21st century, and in some areas significantly more. At increasing warming levels, extreme heat will exceed critical thresholds for health, agriculture and other sectors more frequently (''high confidence''), and it is ''likely'' that cold spells will become less frequent towards the end of the century. For example, by the end of the 21st century, dangerous humid heat thresholds, such as the National Oceanic and Atmospheric Administration (NOAA) heat index (HI) threshold of 41°C, will be exceeded much more frequently under the SSP5-8.5 scenario than under SSP1-2.6 and will affect many regions (''high confidence''). In many tropical regions, the number of days per year where a heat index of 41°C is exceeded would increase by more than 100 days relative to the recent past under SSP5-8.5, while this increase will be limited to less than 50 days under SSP1-2.6 (''high confidence'') (Figure TS.6). The number of days per year where temperature exceeds 35°C would increase by more than 150 days in many tropical areas, such as the Amazon basin and South East Asia, by the end of century for the SSP5-8.5 scenario, while it is expected to increase by less than 60 days in these areas under SSP1-2.6 (except for the Amazon Basin) (''high confidence'') (Figure TS.24). Links to chapters 4.6.1, 11.3, 11.9, 12.4, 12.5.2, Atlas

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'''Figure TS.24 |''' '''Projected change in the mean number of days per year with maximum temperature exceeding 35°C for Coupled Model Intercomparison Project Phase 5 (CMIP5; first column), Phase 6 (CMIP6; second column) and Coordinated Regional Climate Downscaling Experiment (CORDEX; third column) ensembles.''' ''The intent of this figure is to show that there is a consistent message about the patterns of projected change in extreme daily temperatures from the CMIP5, CMIP6 and CORDEX ensembles.'' The map shows the median change in the number of days per year between the mid-century (2041–2060) or end-century (2081–2100) and historical (1995–2014) periods for the CMIP5 and CORDEX RCP8.5 and RCP2.6 scenario ensembles and the CMIP6 SSP5-8.5 and SSP1-2.6 scenario ensembles. Hatching indicates areas where less than 80% of the models agree on the sign of change. Links to chapters Interactive Atlas

'''Wet and dry:''' Compared to the global scale, precipitation internal variability is stronger at the regional scale while uncertainties in observations, models and external forcing are all larger. However, GHG forcing has driven increased contrasts in precipitation amounts between wet and dry seasons and weather regimes over tropical land areas (''medium confidence''), with a detectable precipitation increase in the northern high latitudes (''high confidence'') (Box TS.6). The frequency and intensity of heavy precipitation events have increased over a majority of land regions with good observational coverage (''high confidence''). A majority of land areas have experienced decreases in available water in dry seasons due to human-induced climate change associated with changes in evapotranspiration (''medium confidence''). Global hydrological models project a larger fraction of land areas to be affected by an increase rather than by a decrease in river floods (''medium confidence''). Extreme precipitation and pluvial flooding will increase in many regions around the world on almost all continents (''high confidence''), but regional changes in river floods are more uncertain than changes in pluvial floods because complex hydrological processes, including land cover and human water management, are involved. Links to chapters 8.2.2.1, 8.3.1, Box 8.2, 10.4.1, 11.5, 11.6, 11.9, 12.4, 12.5.1, Atlas.3.1

'''Wind:''' Mean wind speed has decreased over most land areas with good observational coverage (''medium confidence''). It is ''likely'' that the global proportion of major tropical cyclone (TC) intensities (Categories 3–5) over the past four decades has increased. The proportion of intense TCs, average peak TC wind speeds, and peak wind speeds of the most intense TCs will increase on the global scale with increasing global warming (''high confidence''). Links to chapters 11.7.1

'''Snow and ice:''' Many aspects of the cryosphere either have seen significant changes in the recent past or will see them during the 21st century (''high confidence''). Glaciers will continue to shrink and permafrost to thaw in all regions where they are present (''high confidence''). Also, it is ''virtually certain'' that snow cover will experience a decline over most land regions during the 21st century, in terms of water equivalent, extent and annual duration. There is ''high confidence'' that the global warming-induced earlier onset of spring snowmelt and increased melting of glaciers have already contributed to seasonal changes in streamflow in high-latitude and low-elevation mountain catchments. Nevertheless, it is ''very likely'' that some high-latitude regions will experience an increase in winter snow water equivalent due to the effect of increased snowfall prevailing over warming-induced increased snowmelt. (Section TS.2.5) Links to chapters 8.2.2.1, 8.3.1, Box 8.2, 9.4, 9.5.1, 9.5.2, 12.4, Atlas.4–Atlas.9, Atlas.11

'''Coastal and oceanic:''' There is ''high confidence'' that SST will increase in all oceanic regions except the North Atlantic. Regional sea level change has been the main driver of changes in extreme sea levels across the quasi-global tide gauge network over the 20th century (''high confidence''). With the exception of a few regions with substantial land uplift, relative sea level rise is ''very likely to virtually certain'' (depending on the region) to continue during the 21st century, contributing to increased coastal flooding in low-lying areas (''high confidence'') and coastal erosion along most sandy coasts (''high confidence'') over the 21st century. In the open ocean, acidification, changes in sea ice, and deoxygenation have already emerged in many areas (''high confidence''). Marine heatwaves are also expected to increase around the globe over the 21st century (''high confidence''). (Section TS.2.4) Links to chapters Box 9.2, 9.2.1.1, 9.6, 9.6.4, 9.6.4.2, 12.4

'''Other variables and concurrent CID changes:''' It is ''virtually certain'' that atmospheric CO <sub>2</sub> and oceanic pH will increase in all climate scenarios, until net zero CO <sub>2</sub> emissions are achieved (Section TS.2.2). In nearly all regions, there is ''low confidence'' in changes in hail, ice storms, severe storms, dust storms, heavy snowfall, and avalanches, although this does not indicate that these CIDs will not be affected by climate change. For such CIDs, observations are often short-term or lack homogeneity, and models often do not have sufficient resolution or accurate parametrizations to adequately simulate them over climate change time scales. The probability of compound events has increased in the past due to human-induced climate change and will ''likely'' continue to increase with further global warming, including for concurrent heatwaves and droughts, compound flooding, and the possibility of connected sectors experiencing multiple regional extreme events at the same time (for example, in multiple breadbaskets) (''high confidence''). Links to chapters 5.3.4.2, 11.8, Box 11.3, Box 11.4, 12.4

<div id="TS.4.3.2" class="h3-container"></div>

<span id="ts.4.3.2-region-by-region-changes-in-climatic-impact-drivers"></span>
==== 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'''
<div id="TS.4.3.2.1" class="h4-container"></div>

<span id="ts.4.3.2.1-africa"></span>
===== 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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<span id="ts.4.3.2.2-asia"></span>

===== 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

<div id="TS.4.3.2.3" class="h4-container"></div>

<span id="ts.4.3.2.3-australasia"></span>

===== 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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<span id="ts.4.3.2.4-central-and-south-america"></span>

===== 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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<span id="ts.4.3.2.5-europe"></span>

===== 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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<span id="ts.4.3.2.6-north-america"></span>

===== 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

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===== TS.4.3.2.7 Small Islands =====

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'''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

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

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'''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

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

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'''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

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

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'''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

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