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

== Executive Summary ==

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This Atlas chapter assesses changes in mean climate at regional scales, in particular observed trends and their attribution and projected future changes. The main focus is on changes in temperature and precipitation (including snow and derived variables in polar regions) over land regions, though other variables, including for oceanic regions, are also discussed. Projected changes are presented both as relative to levels of global warming and for future time periods under a range of emissions scenarios. In order to facilitate summarizing assessment findings, a new set of WGI reference regions is used within the chapter which were derived following broad consultation and peer review. These are used in other chapters for summarizing regional information. This includes the assessment of climatic impact-driver (CID) changes in Chapter 12, which incorporates the changes in mean climate assessed in the Atlas. Another important new development since AR5 is the AR6 WGI Interactive Atlas, which is described in this chapter and is used to generate results both for the Atlas and other regional chapters. It is also a resource allowing exploration of datasets underpinning assessment findings in other chapters of the report.

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=== Observed Trends and Projections in Regional Climate ===

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'''Most land areas have warmed faster than the global average (''' ''high confidence'' ''') and''' ''very likely'' '''by at least 0.1°C per decade since 1960. A surface temperature change signal has''' ''likely'' '''emerged over all land areas. Many areas''' ''very likely'' '''warmed faster since the 1980s, including areas of northern, eastern and south-western Africa, Australia, Central America, Amazonia and West Antarctica (0.2°C–0.3°C per decade), the Arabian Peninsula, Central and East Asia and Europe (0.3°C–0.5°C per decade), and Arctic and near-Arctic land regions (up to 1°C per decade, or more in a few areas).''' { Figure Atlas.11, Interactive Atlas, [[#Atlas.3.1|Atlas.3.1]] , [[#Atlas.4.2|Atlas.4.2]] , [[#Atlas.5.1.2|Atlas.5.1.2]] , [[#Atlas.5.2.2|Atlas.5.2.2]] , [[#Atlas.5.3.2|Atlas.5.3.2]] , [[#Atlas.5.4.2|Atlas.5.4.2]] , [[#Atlas.5.5.2|Atlas.5.5.2]] , [[#Atlas.6.1.2|Atlas.6.1.2]] , [[#Atlas.6.2.2|Atlas.6.2.2]] , [[#Atlas.7.2|Atlas.7.2]] , [[#Atlas.8.2|Atlas.8.2]] , [[#Atlas.9.2|Atlas.9.2]] , [[#Atlas.10.2|Atlas.10.2]] , [[#Atlas.11.1.2|Atlas.11.1.2]] , [[#Atlas.11.2.2|Atlas.11.2.2]] }

'''Significant positive trends in precipitation have been observed in most of North Asia, parts of West Central Asia, South-Eastern South America, Northern Europe, Eastern North America, Western Antarctica and the Arctic (''' ''medium confidence'' '''). Significant negative trends have been observed in the Horn of Africa and south-west of the state of Western Australia (''' ''high confidence'' '''), parts of the Russian Far East, some parts of the Mediterranean and of the Caribbean, south-east and north-east Brazil, and southern Africa (''' ''medium confidence'' '''), with the trend in southern Africa attributed to anthropogenic (human-caused) warming of the Indian Ocean.''' In many other land areas there are no significant trends in annual precipitation over the period 1960–2015 though increases in average precipitation intensity have been observed in the Sahel and South East Asia ( ''medium confidence'' ). { Figure Atlas.11, Interactive Atlas, [[#Atlas.3.1|Atlas.3.1]] , [[#Atlas.4.2|Atlas.4.2]] , [[#Atlas.5.1.2|Atlas.5.1.2]] , [[#Atlas.5.2.2|Atlas.5.2.2]] , [[#Atlas.5.3.2|Atlas.5.3.2]] , [[#Atlas.5.4.2|Atlas.5.4.2]] , [[#Atlas.5.5.2|Atlas.5.5.2]] , [[#Atlas.6.1.2|Atlas.6.1.2]] , [[#Atlas.6.2.2|Atlas.6.2.2]] , [[#Atlas.7.2|Atlas.7.2]] , [[#Atlas.8.2|Atlas.8.2]] , [[#Atlas.9.2|Atlas.9.2]] , [[#Atlas.10.2|Atlas.10.2]] , [[#Atlas.11.1.2|Atlas.11.1.2]] , [[#Atlas.11.2.2|Atlas.11.2.2]] }

'''The observed warming trends are projected to continue over the 21st century (''' ''high confidence'' ''') and over most land regions at a rate higher than the global average. At a global warming level of 4°C (i.e., relative to an 1850–1900 baseline) it is''' ''likely'' '''that most land areas will experience a further warming (from a 1995–2014 baseline) of at least 3°C and in some areas significantly more, including increases of 4°C–6°C in the Sahara/Sahel; South West, Central and North Asia; Northern South America and Amazonia; Western and Central, and Eastern Europe; and Western, Central and Eastern North America; and up to 8°C or more in some Arctic regions.''' Across each of the continents, higher warming is ''likely'' to occur in northern Africa, the central interior of southern and Western Africa; in North Asia; in Central Australia; in Amazonia; in Northern Europe and northern North America ( ''high confidence'' ). Ranges of regional warming for global warming levels of 1.5°C, 2°C, 3°C and 4°C, and for other time periods and emissions scenarios are available in the Interactive Atlas from Coupled Model Intercomparison Project Phases 5 and 6 (CMIP5, CMIP6) and Coordinated Regional Climate Downscaling Experiment (CORDEX) projections. { Figure Atlas.12, Interactive Atlas, [[#Atlas.4.4|Atlas.4.4]] , [[#Atlas.5.1.4|Atlas.5.1.4]] , [[#Atlas.5.2.4|Atlas.5.2.4]] , [[#Atlas.5.3.4|Atlas.5.3.4]] , [[#Atlas.5.4.4|Atlas.5.4.4]] , [[#Atlas.5.5.4|Atlas.5.5.4]] , [[#Atlas.6.4|Atlas.6.4]] , [[#Atlas.7|Atlas.7.4]] , [[#Atlas.8.4|Atlas.8.4]] , [[#Atlas.9.4|Atlas.9.4]] , [[#Atlas.10.4|Atlas.10.4]] , [[#Atlas.11.4|Atlas.11.4]] }

'''For given global warming levels, model projections from CMIP6 show future regional warming and precipitation changes that are similar to those projected by CMIP5. However, the larger climate sensitivity in some CMIP6 models and differences in the model forcings lead to a wider range of and higher projected regional warming in CMIP6 compared to CMIP5 projections for given time periods and emissions scenarios.''' { Figure Atlas.1 3, [[#Atlas.4.4|Atlas.4.4]] , [[#Atlas.5.1.4|Atlas.5.1.4]] , [[#Atlas.5.2.4|Atlas.5.2.4]] , [[#Atlas.5.3.4|Atlas.5.3.4]] , [[#Atlas.5.4.4|Atlas.5.4.4]] , [[#Atlas.5.5.4|Atlas.5.5.4]] , [[#Atlas.6.1|Atlas.6.1.4]] , [[#Atlas.6.2|Atlas.6.2.4]] , [[#Atlas.7|Atlas.7.4]] , [[#Atlas.8.4|Atlas.8.4]] , [[#Atlas.9.4|Atlas.9.4]] , [[#Atlas.10.4|Atlas.10.4]] , [[#Atlas.11.1.4|Atlas.11.1.4]] , [[#Atlas.11.2.4|Atlas.11.2.4]] }

'''Precipitation will change in most regions, either through changes in mean values or the characteristics of rainy seasons or daily precipitation statistics (''' ''high confidence'' '''). Regions where annual precipitation is''' ''likely'' '''to increase include the Ethiopian Highlands; East, South and North Asia; South-Eastern South America; Northern Europe; northern and Eastern North America and the polar regions. Regions where annual precipitation is''' ''likely'' '''to decrease include northern and south-western southern Africa, Indonesia, the northern Arabian Peninsula, south-western Australia, Central America, South-Western South America and southern Europe.''' Changes in monsoons are ''likely'' to result in increased precipitation in eastern and northern China and in South Asia in summer ( ''high confidence'' ). Precipitation intensity will increase in many areas, including in some where annual mean reductions are ''likely'' (e.g., southern Africa) ( ''high confidence'' ). Ranges of regional mean precipitation change for global warming levels of 1.5°C, 2°C, 3°C and 4°C, and for other time periods and emissions scenarios are available in the Interactive Atlas from CMIP5, CORDEX and CMIP6 projections. { Figure Atlas.1 3, Interactive Atlas, [[#Atlas.4.4|Atlas.4.4]] , [[#Atlas.5.1.4|Atlas.5.1.4]] , [[#Atlas.5.2.4|Atlas.5.2.4]] , [[#Atlas.5.3.4|Atlas.5.3.4]] , [[#Atlas.5.4.4|Atlas.5.4.4]] , [[#Atlas.5.5.4|Atlas.5.5.4]] , [[#Atlas.6.1|Atlas.6.1.4]] , [[#Atlas.6.2|Atlas.6.2.4]] , [[#Atlas.7|Atlas.7.4]] , [[#Atlas.8.4|Atlas.8.4]] , [[#Atlas.9.4|Atlas.9.4]] , [[#Atlas.10.4|Atlas.10.4]] , [[#Atlas.11.1.4|Atlas.11.1.4]] , [[#Atlas.11.2.4|Atlas.11.2.4]] }

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=== Cryosphere, Polar Regions and Small Islands ===

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'''Many aspects of the cryosphere either have seen significant changes in the recent past or will see them during the 21st century (''' ''high confidence'' '''). Snow cover duration has''' ''very likely'' '''reduced over Siberia and Eastern and Northern Europe. Also, it is''' ''virtually certain'' '''that snow cover will experience a decline in these regions and over most of North America during the 21st century, in terms of water equivalent, extent and annual duration. Over the Hindu Kush Himalaya, glacier mass is''' ''likely'' '''to decrease considerably (nearly 50%) under the RCP4.5 and RCP8.5 scenarios.''' Snow cover has declined over Australia as has annual maximum snow mass over North America ( ''medium confidence'' ). Some high-latitude regions have experienced increases in winter snow (parts of North Asia, ''medium confidence'' ) or will do so in the future ( ''very likely'' in parts of northern North America) due to the effect of increased snowfall prevailing over warming-induced increased snowmelt. { [[#2.3.2.2|2.3.2.2]] , [[#3.4.2|3.4.2]] ,, [[#Atlas.5.2.2|Atlas.5.2.2]] , [[#Atlas.5.3.4|Atlas.5.3.4]] , [[#Atlas.6.2|Atlas.6.2]] , [[#Atlas.8.2|Atlas.8.2]] , [[#Atlas.8.4|Atlas.8.4]] , [[#Atlas.9.2|Atlas.9.2]] , [[#Atlas.9.4|Atlas.9.4]] }

'''It is''' ''very likely'' '''that the Arctic has warmed at more than twice the global rate over the past 50 years and that the Antarctic Peninsula experienced a strong warming trend starting in 1950s. It is''' ''likely'' '''that Arctic annual precipitation has increased, with the highest increases during the cold season. Antarctic precipitation and surface mass balance showed a significant positive trend over the 20th century, while strong interannual variability masks any existing trend over recent decades''' [[#footnote-000|1]] '''(''' ''medium confidence'' ''').''' Significant warming trends are observed in other West Antarctic regions and at selected stations in East Antarctica since the 1950s ( ''medium confidence'' ). Under all assessed emissions scenarios, both polar regions are ''very likely'' to have higher annual mean surface air temperatures and more precipitation, with temperature increases higher than the global mean, most prominently in the Arctic. { [[#Atlas.11.1.2|Atlas.11.1.2]] , [[#Atlas.11.1.4|Atlas.11.1.4]] , [[#Atlas.11.2.2|Atlas.11.2.2]] , [[#Atlas.11.2.4|Atlas.11.2.4]] }

'''It is''' ''very likely'' '''that most Small Islands have warmed over the period of instrumental records. Precipitation has''' ''likely'' '''decreased since the mid-20th century in some parts of the Pacific poleward of 20° latitude in both hemispheres and in the Caribbean in June–July–August. It is''' ''very likely'' '''that sea levels will continue to rise in Small Island regions and that this will result in increased coastal flooding.''' Observed temperature trends are generally in the range of 0.15°C–0.2°C per decade. Rainfall trends in most other Pacific Ocean and Indian Ocean Small Islands are mixed and largely non-significant. There is ''limited evidence'' and ''low agreement'' on the cause of the Caribbean drying trend, though it is ''likely'' that both this and the Pacific drying trends will continue in coming decades with drying also projected in the part of the Western Indian and Atlantic oceans. Small Island regions in the western and Equatorial Pacific Ocean, and in the northern Indian Ocean are ''likely'' to be wetter in the future. { Cross-Chapter Box Atlas.2, [[#Atlas.10.2|Atlas.10.2]] , [[#Atlas.10.4|Atlas.10.4]] }

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=== Model Evaluation, Technical Infrastructure and the Interactive Atlas ===

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'''The regional performance of CMIP6 global climate models (GCMs) has improved overall compared to CMIP5 in simulating mean temperature and precipitation, though large errors still exist in some regions (''' ''high confidence'' '''). In particular, improvements have been seen over Africa which has belatedly become a focus for GCM model development''' '''.''' Other specific improvements include over East Asia for temperature and the winter monsoon, over parts of South Asia for the summer monsoon, over Australia (including influences of modes of variability), in simulation of Antarctic temperatures and Arctic sea ice. Notable errors include large cold biases in mountain ranges in South Asia, a significant wet bias over Central Asia, in the East Asia summer monsoon and in Antarctic precipitation. An in-depth evaluation of CMIP6 models is lacking for several regions (North and South East Asia, parts of West Central Asia, Central and South America), though CMIP5 models have been evaluated for many of these. { [[IPCC:Wg1:Chapter:Chapter-3#3.3.1|3.3.1]] , [[IPCC:Wg1:Chapter:Chapter-3#3.3.2|3.3.2]] , [[#Atlas.4.3|Atlas.4.3]] , [[#Atlas.5.1.3|Atlas.5.1.3]] , [[#Atlas.5.2.3|Atlas.5.2.3]] , [[#Atlas.5.3.3|Atlas.5.3.3]] , [[#Atlas.5.4.3|Atlas.5.4.3]] , [[#Atlas.5.5.3|Atlas.5.5.3]] , [[#Atlas.6.1|Atlas.6.1.3]] , [[#Atlas.6.2|Atlas.6.2.3]] , [[#Atlas.7|Atlas.7.3]] , [[#Atlas.8.3|Atlas.8.3]] , [[#Atlas.9.3|Atlas.9.3]] , [[#Atlas.10.3|Atlas.10.3]] , [[#Atlas.11.1.3|Atlas.11.1.3]] , [[#Atlas.11.2.3|Atlas.11.2.3]] }

'''Since AR5, the improvement in regional climate modelling and the growing availability of regional simulations through coordinated dynamical downscaling initiatives such as CORDEX, have advanced the understanding of regional climate variability, adding value to CMIP global models, particularly in complex topography zones, coastal areas and small islands, and in the representation of extremes (''' ''high confidence'' ''').''' In particular, regional climate models (RCMs) with polar-optimized physics are important for estimating the regional and local surface mass balance and are improved compared to reanalyses and GCMs when evaluated with observations ( ''high confidence'' ). There is still a lack of high-quality and high-resolution observational data to assess observational uncertainty in climate studies, and this compromises the ability to evaluate models ( ''high confidence'' ). { [[#Atlas.4.3|Atlas.4.3]] , [[#Atlas.5.1.3|Atlas.5.1.3]] , [[#Atlas.5.2.3|Atlas.5.2.3]] , [[#Atlas.5.3.3|Atlas.5.3.3]] , [[#Atlas.5.4.3|Atlas.5.4.3]] , [[#Atlas.5.5.3|Atlas.5.5.3]] , [[#Atlas.6.1|Atlas.6.1.3]] , [[#Atlas.6.2|Atlas.6.2.3]] , [[#Atlas.7|Atlas.7.3]] , [[#Atlas.8.3|Atlas.8.3]] , [[#Atlas.9.3|Atlas.9.3]] , [[#Atlas.10.3|Atlas.10.3]] , [[#Atlas.11.1.3|Atlas.11.1.3]] , [[#Atlas.11.2.3|Atlas.11.2.3]] }

'''Significant improvements in technical infrastructure, open tools and methodologies for accessing and analysing observed and simulated climate data, and the progressive adoption of FAIR (findability, accessibility, interoperability and reusability) data principles have''' ''very likely'' '''broadened the ability to interact with these data for a wide range of activities, including fundamental climate research, providing inputs into assessments of impacts, building resilience and developing adaptations.''' Tools to analyse and assess climate information have improved to allow development of information that goes beyond averages (e.g., on future climate thresholds and extremes) and that is relevant for regional climate risk assessments. { Atlas.2.2, [[#Atlas.2.3|Atlas.2.3]] }

'''The Interactive Atlas is a new WGI product developed to take advantage of the interactivity offered by web applications by allowing flexible and expanded exploration of some key products underpinning the assessment (including extreme indices and climatic impact-drivers).''' This provides a transparent interface for access to authoritative IPCC results, facilitating their use in applications and climate services. The Interactive Atlas implements FAIR principles and builds on open tools and, therefore, is an important step towards making IPCC results more reproducible and reusable. { Atlas.2, Interactive Atlas }

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