The IPCC is the Intergovernmental Panel on Climate Change. It is the UN body for assessing the science related to climate change.

BASICS

Human activity is warming the planet. The majority of the warming comes from burning fossil fuels (such as coal, oil or gas) which emit carbon dioxide which thickens the atmosphere, so less heat escapes.

There is more carbon dioxide in the atmosphere now than there has been for a million years. And we are still burning it by using petrol or diesel powered cars or using gas central heating.

This climate change is causing major changes in weather causing droughts, floods, wildfires, heatwaves and violent storms. Droughts threaten our food supply. And its getting more severe.

DETAIL

1 It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere (the frozen water part of the Earth system) and biosphere (zone of life on Earth) have occurred.

2 The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.

3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5 (the 5th climate change report).

4 Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C with a narrower range compared to AR5.

The Future

5 Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.

6 Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.

7 Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.

8 A projected southward shift and intensification of Southern Hemisphere summer mid-latitude storm tracks and associated precipitation is likely in the long term under high green house gas emissions scenarios, but in the near term the effect of stratospheric ozone recovery counteracts these changes (high confidence). There is medium confidence in a continued poleward shift of storms and their precipitation in the North Pacific, while there is low confidence in projected changes in the North Atlantic storm tracks.

9 Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.

DETAIL

Item 1

Since AR5 in 2011 GHG (Green House Gas) concentrations have continued to increase in the atmosphere, reaching annual averages of 410 ppm for carbon dioxide (CO2), 1866 ppb for methane (CH4), and 332 ppb for nitrous oxide (N2O). Land and ocean have taken up a near-constant proportion (globally about 56% per year) of CO2 emissions from human activities over the past six decades, with regional differences (high confidence)

Each of the last four decades has been successively warmer than any decade that preceded it since 1850. Global surface temperature in the first two decades of the 21st century was about 1°C higher than 1850-1900 with larger increases over land (1.6°C) than over the ocean (0.9°C). The estimated increase in global surface temperature since AR5 is principally due to further warming since 2003–2012.

It is likely that GHGs contributed a warming of 1.0°C to 2.0°C, other human drivers (principally aerosols, which are tiny particles in the air that can be produced when we burn different types of fossil fuels, often in cars and factories), contributed a cooling of 0.0°C to 0.8°C.

Globally averaged precipitation over land has likely increased since 1950, with a faster rate of increase since the 1980s (medium confidence). It is likely that human influence contributed to the pattern of observed precipitation changes since the mid-20th century, and extremely likely that human influence contributed to the pattern of observed changes in near-surface ocean salinity. Mid-latitude storm tracks have likely shifted poleward in both hemispheres since the 1980s, with marked seasonality in trends (medium confidence). For the Southern Hemisphere, human influence very likely contributed to the poleward shift of the closely related extratropical jet in austral summer.

Human influence is very likely the main driver of the global retreat of glaciers since the 1990s and the decrease in Arctic sea ice area between 1979–1988 and 2010–2019 (about 40% in September and about 10% in March). There has been no significant trend in Antarctic sea ice area from 1979 to 2020 due to regionally opposing trends and large internal variability. Human influence very likely contributed to the decrease in Northern Hemisphere spring snow cover since 1950. It is very likely that human influence has contributed to the observed surface melting of the Greenland Ice Sheet over the past two decades, but there is only limited evidence, with medium agreement, of human influence on the Antarctic Ice Sheet mass loss.

It is virtually certain that the global upper ocean (0–700m) has warmed since the 1970s and extremely likely that human influence is the main driver. It is virtually certain that human-caused CO2 emissions are the main driver of current global acidification of the surface open ocean. There is high confidence that oxygen levels have dropped in many upper ocean regions since the mid-20th century, and medium confidence that human influence contributed to this drop.

Global mean sea level increased by 0.20m between 1901 and 2018. The average rate of sea level rise was 1.3mm/yr between 1901 and 1971, increasing to 1.9mm/yr between 1971 and 2006, and further increasing to 3.7mm/yr between 2006 and 2018 (high confidence). Human influence was very likely the main driver of these increases since at least 1971.

Climate zones have shifted poleward in both hemispheres, and the growing season has on average lengthened by up to two days per decade since the 1950s in the Northern Hemisphere outside the tropics (high confidence).

Item 2

In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of Methane (CH4) and Nitrous Oxide (N2O) were higher than at any time in at least 800,000 years (very high confidence). Since 1750, increases in CO2 (47%) and CH4 (156%) concentrations far exceed, and increases in N2O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence).

Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years (high confidence). Temperatures during the most recent decade (2011–2020) exceed those of the most recent multi-century warm period, around 6500 years ago (0.2°C to 1°C relative to 1850–1900) (medium confidence). Prior to that, the next most recent warm period was about 125,000 years ago when the multi-century temperature (0.5°C to 1.5°C relative to 1850–1900) overlaps the observations of the most recent decade (medium confidence).

In 2011–2020, annual average Arctic sea ice area reached its lowest level since at least 1850 (high confidence). Late summer Arctic sea ice area was smaller than at any time in at least the past 1000 years (medium confidence). The global nature of glacier retreat, with almost all of the world’s glaciers retreating synchronously, since the 1950s is unprecedented in at least the last 2000 years (medium confidence).

Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years (high confidence). The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago) (medium confidence). A long-term increase in surface open ocean acidity occurred over the past 50 million years (high confidence), and surface open ocean acidity as low as recent decades is unusual in the last 2 million years (medium confidence).

Item 3

It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with high confidence that human-induced climate change is the main driver of these changes. Some recent hot extremes observed over the past decade would have been extremely unlikely to occur without human influence on the climate system. Marine heatwaves have approximately doubled in frequency since the 1980s (high confidence), and human influence has very likely contributed to most of them since at least 2006.

The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver. Human-induced climate change has contributed to increases in agricultural and ecological droughts15 in some regions due to increased land evapotranspiration16 (medium confidence).

Decreases in global land monsoon precipitation from the 1950s to the 1980s are partly attributed to human-caused Northern Hemisphere aerosol emissions, but increases since then have resulted from rising GHG concentrations and decadal to multi-decadal internal variability (medium confidence). Over South Asia, East Asia and West Africa increases in monsoon precipitation due to warming from GHG emissions were counteracted by decreases in monsoon precipitation due to cooling from human-caused aerosol emissions over the 20th century (high confidence). Increases in West African monsoon precipitation since the 1980s are partly due to the growing influence of GHGs and reductions in the cooling effect of human-caused aerosol emissions over Europe and North America (medium confidence)

It is likely that the global proportion of major (Category 3–5) tropical cyclone occurrence has increased over the last four decades, and the latitude where tropical cyclones in the western North Pacific reach their peak intensity has shifted northward; these changes cannot be explained by internal variability alone (medium confidence). There is low confidence in long-term (multi-decadal to centennial) trends in the frequency of all-category tropical cyclones. Event attribution studies and physical understanding indicate that human-induced climate change increases heavy precipitation associated with tropical cyclones (high confidence) but data limitations inhibit clear detection of past trends on the global scale.

Human influence has likely increased the chance of compound extreme events since the 1950s. This includes increases in the frequency of concurrent heatwaves and droughts on the global scale (high confidence); fire weather in some regions of all inhabited continents (medium confidence); and compound flooding in some locations (medium confidence).

Splitting the world land mass into 45 areas:
* observed changes in hot extremes have increased in 41 areas and decreased in none
* observed changes in heavy precipitation have increased in 19 areas and decreased in none
* observed changes in agricultural and ecological drought have increased in 12 areas and decreased in 1.

Item 4

Human-caused warming energy of 2.72 W/m2 in 2019 relative to 1750 has warmed the climate system. This warming is mainly due to increased GHG concentrations, partly reduced by cooling due to increased aerosol concentrations. The warming energy has increased by 0.43 W/m2 (19%) relative to AR5.

Human-caused net positive warming energy causes an accumulation of additional energy (heating) in the climate system, partly reduced by increased energy loss to space in response to surface warming. The observed average rate of heating of the climate system increased from 0.50 W/m2 for the period 1971–2006, to 0.79 W/m2 for the period 2006–201820 (high confidence). Ocean warming accounted for 91% of the heating in the climate system, with land warming, ice loss and atmospheric warming accounting for about 5%, 3% and 1%, respectively (high confidence).

Heating of the climate system has caused global mean sea level rise through ice loss on land and thermal expansion from ocean warming. Thermal expansion explained 50% of sea level rise during 1971–2018, while ice loss from glaciers contributed 22%, ice sheets 20% and changes in land water storage 8%. The rate of ice sheet loss increased by a factor of four between 1992–1999 and 2010–2019. Together, ice sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006-2018. (high confidence)

Item 5

Compared to 1850–1900, global surface temperature averaged over 2081–2100 is very likely to be higher by 1.0°C to 1.8°C under the very low GHG emissions scenario considered, by 2.1°C to 3.5°C in the intermediate scenario and by 3.3°C to 5.7°C under the very high GHG emissions scenario (SSP5-8.5)24. The last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago (medium confidence).

Based on the assessment of multiple lines of evidence, global warming of 2°C, relative to 1850–1900, would be exceeded during the 21st century under the high and very high GHG emissions scenarios considered in this report. Global warming of 2°C would extremely likely be exceeded in the intermediate scenario. Under the very low and low GHG emissions scenarios, global warming of 2°C is extremely unlikely to be exceeded, or unlikely to be exceeded. Crossing the 2°C global warming level in the mid-term period (2041–2060) is very likely to occur under the very high GHG emissions scenario, likely to occur under the high GHG emissions scenario, and more likely than not to occur in the intermediate GHG emissions scenario.

Global warming of 1.5°C relative to 1850-1900 would be exceeded during the 21st century under the intermediate, high and very high scenarios. In the near term (2021-2040), the 1.5°C global warming level is very likely to be exceeded under the very high GHG emissions scenario, likely to be exceeded under the intermediate and high GHG emissions scenarios, more likely than not to be exceeded under the low GHG emissions scenario and more likely than not to be reached under the very low GHG emissions scenario. Furthermore, for the very low GHG emissions scenario, it is more likely than not that global surface temperature would decline back to below 1.5°C toward the end of the 21st century, with a temporary overshoot of no more than 0.1°C above 1.5°C global warming.

Global surface temperature in any single year can vary above or below the long-term human-induced trend, due to substantial natural variability. The occurrence of individual years with global surface temperature change above a certain level, for example 1.5°C or 2ºC, relative to 1850–1900 does not imply that this global warming level has been reached.

Item 6

It is virtually certain that the land surface will continue to warm more than the ocean surface (likely 1.4 to 1.7 times more). It is virtually certain that the Arctic will continue to warm more than global surface temperature, with high confidence above two times the rate of global warming.

With every additional increment of global warming, changes in extremes continue to become larger. For example, every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes, including heatwaves (very likely), and heavy precipitation (high confidence), as well as agricultural and ecological droughts in some regions (high confidence). Discernible changes in intensity and frequency of meteorological droughts, with more regions showing increases than decreases, are seen in some regions for every additional 0.5°C of global warming (medium confidence). Increases in frequency and intensity of hydrological droughts become larger with increasing global warming in some regions (medium confidence). There will be an increasing occurrence of some extreme events unprecedented in the observational record with additional global warming, even at 1.5°C of global warming. Projected percentage changes in frequency are higher for rarer events (high confidence).

Some mid-latitude and semi-arid regions, and the South American Monsoon region, are projected to see the highest increase in the temperature of the hottest days, at about 1.5 to 2 times the rate of global warming (high confidence). The Arctic is projected to experience the highest increase in the temperature of the coldest days, at about 3 times the rate of global warming (high confidence). With additional global warming, the frequency of marine heatwaves will continue to increase (high confidence), particularly in the tropical ocean and the Arctic (medium confidence).

It is very likely that heavy precipitation events will intensify and become more frequent in most regions with additional global warming. At the global scale, extreme daily precipitation events are projected to intensify by about 7% for each 1°C of global warming (high confidence). The proportion of intense tropical cyclones (categories 4-5) and peak wind speeds of the most intense tropical cyclones are projected to increase at the global scale with increasing global warming (high confidence).

Additional warming is projected to further amplify permafrost thawing, and loss of seasonal snow cover, of land ice and of Arctic sea ice (high confidence). The Arctic is likely to be practically sea ice free in September at least once before 2050, with more frequent occurrences for higher warming levels. There is low confidence in the projected decrease of Antarctic sea ice.

Item 7

There is strengthened evidence since AR5 that the global water cycle will continue to intensify as global temperatures rise (high confidence), with precipitation and surface water flows projected to become more variable over most land regions within seasons (high confidence) and from year to year (medium confidence). The average annual global land precipitation is projected to increase by 0–5% under the very low GHG emissions scenario, 1.5-8% for the intermediate GHG emissions scenario and 1–13% under the very high GHG emissions scenario by 2081–2100 relative to 1995-2014 (likely ranges). Precipitation is projected to increase over high latitudes, the equatorial Pacific and parts of the monsoon regions, but decrease over parts of the subtropics and limited areas in the tropics (very likely). The portion of the global land experiencing detectable increases or decreases in seasonal mean precipitation is projected to increase (medium confidence). There is high confidence in an earlier onset of spring snowmelt, with higher peak flows at the expense of summer flows in snow-dominated regions globally.

A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought (high confidence), but the location and frequency of these events depend on projected changes in regional atmospheric circulation, including monsoons and mid-latitude storm tracks. It is very likely that rainfall variability related to the El Niño–Southern Oscillation is projected to be amplified by the second half of the 21st century.

Monsoon precipitation is projected to increase in the mid- to long term at global scale, particularly over South and Southeast Asia, East Asia and West Africa apart from the far west Sahel (high confidence). The monsoon season is projected to have a delayed onset over North and South America and West Africa (high confidence) and a delayed retreat over West Africa (medium confidence).

A projected southward shift and intensification of Southern Hemisphere summer mid-latitude storm tracks and associated precipitation is likely in the long term under high GHG emissions scenarios, but in the near term the effect of stratospheric ozone recovery counteracts these changes (high confidence). There is medium confidence in a continued poleward shift of storms and their precipitation in the North Pacific, while there is low confidence in projected changes in the North Atlantic storm tracks.

Item 8

While natural land and ocean carbon sinks are projected to take up, in absolute terms, a progressively larger amount of CO2 under higher compared to lower CO2 emissions scenarios, they become less effective, that is, the proportion of emissions taken up by land and ocean decrease with increasing cumulative CO2 emissions. This is projected to result in a higher proportion of emitted CO2 remaining in the atmosphere (high confidence)

Based on model projections, under the intermediate scenario that stabilizes atmospheric CO2 concentrations this century, the rates of CO2 taken up by the land and oceans are projected to decrease in the second half of the 21st century (high confidence). Under the very low and low GHG emissions scenarios, where CO2 concentrations peak and decline during the 21st century, land and oceans begin to take up less carbon in response to declining atmospheric CO2 concentrations (high confidence) and turn into a weak net source by 2100 (medium confidence). It is very unlikely that the combined global land and ocean sink will turn into a source by 2100
under scenarios without net negative emissions.

The magnitude of feedbacks between climate change and the carbon cycle becomes larger but also more uncertain in high CO2 emissions scenarios (very high confidence). However, climate model projections show that the uncertainties in atmospheric CO2 concentrations by 2100 are dominated by the differences between emissions scenarios (high confidence). Additional ecosystem responses to warming not yet fully included in climate models, such as CO2 and CH4 fluxes from wetlands, permafrost thaw and wildfires, would further increase concentrations of these gases in the atmosphere (high confidence).

Item 9

Past GHG emissions since 1750 have committed the global ocean to future warming (high confidence). Over the rest of the 21st century, likely ocean warming ranges from 2–8 times the 1971–2018 change. Based on multiple lines of evidence, upper ocean stratification (virtually certain), ocean acidification (virtually certain) and ocean deoxygenation (high confidence) will continue to increase in the 21st century, at rates dependent on future emissions. Changes are irreversible on centennial to millennial time scales in global ocean temperature (very high confidence), deep ocean acidification (very high confidence) and deoxygenation (medium confidence).

Mountain and polar glaciers are committed to continue melting for decades or centuries (very high confidence). Loss of permafrost carbon following permafrost thaw is irreversible at centennial timescales (high confidence). Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and likely for the Antarctic Ice Sheet. There is high confidence that total ice loss from the Greenland Ice Sheet will increase with cumulative emissions. There is limited evidence for low-likelihood, high-impact outcomes (resulting from ice sheet instability processes characterized by deep uncertainty and in some cases involving tipping points) that would strongly increase ice loss from the Antarctic Ice Sheet for centuries under high GHG emissions scenarios.

It is virtually certain that global mean sea level will continue to rise over the 21st century. Relative
to 1995-2014, the likely global mean sea level rise by 2100 is:

• 0.28-0.55 m under very low GHG,
• 0.32-0.62 m under low GHG,
• 0.44-0.76 m under intermediate GHG, and
• 0.63-1.01 m under very high GHG.

And by 2150 is:

• 0.37-0.86 m under very GHG,
• 0.46-0.99 m under low GHG
• 0.66-1.33 m under intermediate GHG, and
• 0.98-1.88 m under very high GHG (medium confidence).

Global mean sea level rise above the likely range – approaching 2 m by 2100 and 5 m by 2150 under a very high GHG (low confidence) – cannot be ruled out due to deep uncertainty in ice sheet processes.

In the longer term, sea level is committed to rise for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and will remain elevated for thousands of years (high confidence). Over the next 2000 years, global mean sea level will rise by about 2 to 3 m if warming is limited to 1.5°C, 2 to 6 m if limited to 2°C and 19 to 22 m with 5°C of warming, and it will continue to rise over subsequent millennia (low confidence). Projections of multi-millennial global mean sea level rise are consistent with reconstructed levels during past warm climate periods: likely 5–10 m higher than today around 125,000 years ago, when global temperatures were very likely 0.5°C–1.5°C higher than 1850–1900; and very likely 5–25 m higher roughly 3 million years ago, when global temperatures were 2.5°C–4°C higher (medium confidence).