The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports that review scientific information about climate change. Three working groups (WGI, WGII, and WGIII) each focused on different topics: WGI studied the physical science basis of climate change; WGII examined impacts, adaptation, and vulnerability; and WGIII looked at ways to reduce climate change. The first report was published in 2021, the second in February 2022, and the third in April 2022. A final summary report was completed in March 2023. This report included a summary for policymakers and was used as the basis for the 2023 United Nations Climate Change Conference (COP28) in Dubai.

The first working group (WGI) released its report on August 9, 2021, titled Climate Change 2021: The Physical Science Basis. A total of 234 scientists from 66 countries helped write this report. The authors used more than 14,000 scientific papers to create a 3,949-page report, which was approved by 195 governments. The Summary for Policymakers (SPM) was written by scientists and agreed to by the 195 governments in the IPCC over five days before August 6, 2021.

The report includes guidelines for both short-term and long-term responses to climate change. It states that the main cause of increased global warming is higher carbon dioxide (CO₂) emissions. The report says it is likely or very likely that global temperatures will rise above 1.5°C under higher emission scenarios.

According to the WGI report, avoiding warming of 1.5°C (2.7°F) or 2.0°C (3.6°F) is only possible if there are large and immediate reductions in greenhouse gas emissions. The Guardian described the report as "its starkest warning yet" about "major, unavoidable, and lasting climate changes." This message was also shared by many newspapers, political leaders, and activists worldwide.

Production

In April 2016, during the 43rd session held in Nairobi, Kenya, the topics for three Special Reports (SR) and one methodology report about Greenhouse Gas (GHG) inventories for the AR6 assessment cycle were decided. These reports were completed during the time between the completion of the Fifth Assessment Report and the release of the Sixth Assessment Report.

The Sixth Assessment Report includes the work of three Working Groups (WG I, II, and III) and a synthesis report that concluded the assessment in early 2023. The reports were released in the following order:

• The Physical Science Basis of Climate Change in August 2021 (WGI contribution)
• Impacts, Adaptation, and Vulnerability in February 2022 (WGII contribution)
• Mitigation of Climate Change in April 2022 (WGIII contribution)
• Synthesis Report in March 2023

Geopolitics was included in climate models for the first time through five Shared Socioeconomic Pathways (SSP): SSP1 "Taking the Green Road," SSP2 "Middle of the Road," SSP3 "A Rocky Road," SSP4 "A Road Divided," and SSP5 "Taking the Highway." These pathways were published in 2016.

These pathways assume that international cooperation and a global increase in GDP will help societies adapt to climate change. The geopolitical pathways were one of the sources used to create the Shared Socioeconomic Pathways in the report, along with other sources. One assumption is that enough GDP and technology from fossil fuel development will allow societies to adapt even to a 5.0 °C (9.0 °F) temperature rise. Some experts believe that while the chances of the worst-case scenario (5 °C) and the best-case scenario (1.5 °C) are currently low, the most likely outcome is around 3.0 °C (5.4 °F).

The release dates of special IPCC reports during the same assessment cycle were:

• Special Report on Global Warming of 1.5 °C (SR15) in October 2018
• 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories in May 2019
• Special Report on Climate Change and Land (SRCCL) in August 2019
• Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) in September 2019

Working Group 1 report (physical science basis)

A total of 234 scientists from 66 countries helped create the first of three working group reports. Working Group 1 (WGI) published Climate Change 2021: The Physical Science Basis. The report’s authors used more than 14,000 scientific papers to create a 3,949-page document. This report was approved by 195 governments. The Summary for Policymakers (SPM) was written by scientists and agreed to line-by-line by the 195 governments in the IPCC during five days before 6 August 2021. It was published on Monday, 9 August 2021.

According to the report, avoiding warming of 1.5°C or 2°C requires large and immediate reductions in greenhouse gas emissions. A news article in The Guardian called the report "its starkest warning yet" about "major unavoidable and permanent climate changes." Many other newspapers around the world shared this message.

The Technical Summary (TS) includes more details than the Summary for Policymakers (SPM) but less than the full report. An interactive atlas was created to allow analysis of data about climate change over different areas and times.

The Working Group 1 (WGI) report, Climate Change 2021: The Physical Science Basis, has thirteen chapters and focuses on the basic agreement among scientists about the causes and effects of human greenhouse gas emissions. Compared to earlier reports, this one includes more information about the regional effects of climate change. However, more research is needed about climate change in eastern and central North America. Sea-level rise by 2100 is likely to be between half and one meter, but two to five meters is not ruled out. This is because the processes that cause ice sheets to melt are still not fully understood.

The report estimates that for each doubling of carbon dioxide in the atmosphere, global temperatures could rise between 2.5°C (4.5°F) and 4.0°C (7.2°F). The best estimate is 3°C. In all Shared Socioeconomic Pathways, temperatures reach the 1.5°C warming limit at least for some time in the middle of the 21st century. However, Joeri Rogelj, a lead IPCC author, said it is possible to avoid 1.5°C of warming entirely if the world reduces emissions by 50% by 2030 and by 100% by 2050. If emissions are not cut quickly, it may no longer be possible to prevent 1.5°C of warming. SSP1-1.9 is a new pathway that models how people could keep warming below 1.5°C. In this scenario, global temperatures peak at 1.6°C between 2041 and 2060 and then decrease slightly.

The IPCC Sixth Assessment Report did not estimate the likelihood of these scenarios.

In 2020, a commentary described SSP5–8.5 as highly unlikely, SSP3–7.0 as unlikely, and SSP2–4.5 as likely.

In January 2025, a revised assessment by Hausfather estimated that current policies would lead to about 2.7°C of warming by 2100. Including uncertainties, the range of warming is estimated to be between 1.9°C and 3.7°C. The paper also states that current emissions policies align most closely with, or slightly fall below, SSP2-4.5 rather than SSP3-7.0.

According to coauthors of the Sixth Assessment Report, the most likely temperature rise by the end of the century is about 3°C, which falls in the middle of the range from 1.5°C to 5°C. It is likely that 1.5°C of warming will be reached before 2040. The report also highlights that the risks from combined extreme weather events are higher than in previous IPCC reports. The famous "hockey stick" graph, which shows historical temperature trends, has been updated.

Extreme weather is expected to increase as temperatures rise. Combined effects, such as heat and drought happening together, may have greater impacts on society. The report includes a major change from previous IPCC reports: scientists can now better link specific extreme weather events to climate change.

To stay below 1.5°C of warming, the global carbon budget allows for 500 billion additional tonnes of greenhouse gas emissions. To have a 50% chance of staying below 1.5°C, the world must reach net zero emissions before 2050. For a 67% chance, the budget is 400 billion tonnes, and for an 83% chance, it is 300 billion tonnes. The report emphasizes the importance of quickly reducing methane emissions to buy time for long-term carbon dioxide reductions.

Future warming will increase the frequency and intensity of extreme weather events. Even with 1.5°C of warming, some extreme events will occur more often than ever recorded. The likelihood of rare events increasing is also higher.

The frequency and intensity of such events will increase significantly with warming, as shown in the following table.

Working Group 2 report (impacts, adaptation and vulnerability)

The second part of the report, created by Working Group II (WGII), was released on 28 February 2022. The report is titled Climate Change 2022: Impacts, Adaptation & Vulnerability. It is 3,675 pages long, with a 37-page summary for policymakers. The report discusses how climate change affects nature and human activities. Topics include loss of wildlife, movement of people, risks to cities and rural areas, human health, food supplies, water shortages, and energy use. It also explains ways to reduce these risks and how making development more resistant to climate change can help create a more sustainable future.

The report was published during the first week of the 2022 Russian invasion of Ukraine. During the conflict, Ukrainian leaders linked the war to the world’s reliance on oil, and a Russian official, Oleg Anisimov, apologized for the war despite possible consequences. Ukrainian leaders also asked that news about the war not distract from the WGII report.

The report states that climate change effects are worse than earlier predictions and affect all parts of the world. At least 3.3 billion people, or about 40% of the world’s population, are now in the most serious category of being "highly vulnerable," with the worst effects in poorer countries. If emissions continue at the current rate, Africa could lose 30% of its land used to grow maize and 50% of its land used for beans. One billion people could face flooding from rising sea levels. Climate change also increases the risk of disease outbreaks, such as the COVID-19 pandemic. The report says China will face the highest financial costs if temperatures rise further. Impacts will include food shortages, water shortages, flooding in coastal areas, and stronger storms. In some parts of China, temperatures may become too hot for humans and other mammals to survive for more than six hours. The report lists 127 different negative effects of climate change, some of which cannot be reversed.

People can reduce the effects of climate change through actions called adaptation. Progress has been made in all areas, but it is uneven. Many efforts focus on short-term risks rather than long-term changes. However, many adaptation actions can help reduce climate risks and also support goals like improving health, food, and water access. For example, improving water management and irrigation helps reduce vulnerability and can provide economic and environmental benefits. Actions like planting trees, diversifying farms, and growing food in cities can increase food supplies and improve sustainability.

The report also emphasizes the need to protect nature to help reduce the effects of climate change. It states that protecting about 30% to 50% of Earth’s land, water, and ocean areas is needed to keep ecosystems strong. The report is critical of using technology to remove carbon dioxide from the air and suggests that city planning can help reduce emissions through public transportation and renewable energy. It warns that some strategies, like managing sunlight to cool the planet or planting forests in unsuitable areas, carry high risks.

The report highlights that some effects of climate change cannot be avoided, even with efforts to adapt. These include droughts, floods, and heatwaves that are becoming more common. A large loss of wildlife is already happening. Limiting warming to below 1.5°C would reduce future harm, but not all harm can be avoided. Wealthier countries have previously avoided taking responsibility for these harms.

The report says even a short period of exceeding the 1.5°C limit will cause harm to people and nature. Some effects, like the release of more greenhouse gases or damage to ecosystems, may be permanent. If global temperatures rise by 1.5°C above pre-industrial levels, creating climate-resilient development will be harder. If temperatures rise by more than 2°C, it may become impossible in some areas.

Although the report shows serious challenges, it says it is still possible to limit warming to 1.5°C by making large reductions in greenhouse gas emissions immediately. Climate-resilient development can help both reduce risks and lower emissions, but it requires cooperation between countries and local groups.

Working Group 3 report (mitigation of climate change)

The report was presented on April 4, 2022. Some people are concerned that the report’s final conclusions may be weakened, as reports are often changed before being finalized. According to The Observer, some countries have tried to make changes that could reduce the strength of the final warnings in the report.

The report includes new ideas, such as involving youth, indigenous people, cities, and businesses in solving climate change problems. It says, “International cooperation is a critical enabler for achieving ambitious climate change mitigation goals.” To prevent global temperatures from rising more than 2 degrees above preindustrial levels, international cooperation must be stronger than it is now, especially because many developing countries need help from other countries to take strong climate action.

The report states that demand-side mitigation measures—such as changing how people use energy—could reduce greenhouse gas (GHG) emissions by 40–70% by 2050 compared to current national pledges made before 2020. For these measures to work, they must be connected to improving basic wellbeing for all people.

The report concludes that achieving net zero emissions requires using carbon dioxide removal (CDR) technologies. It explains that all global plans to limit warming to 1.5°C or 2°C involve quickly and deeply reducing GHG emissions in all sectors. These plans include switching from fossil fuels without carbon capture and storage (CCS) to low- or zero-carbon energy sources like renewables or fossil fuels with CCS, demand-side measures, improving efficiency, reducing non-CO₂ emissions, and using CDR methods to balance remaining emissions. The report compares different CDR methods, such as agroforestry, reforestation, blue carbon management, and peatland restoration.

Cities have the potential to greatly reduce GHG emissions. If cities take full-scale mitigation action, their emissions could be reduced to nearly zero, with a small remaining amount of 3 gigatonnes of CO₂-equivalent in the worst-case scenario. City planning that supports mixed-use spaces, public transit, walking, cycling, and shared vehicles can reduce urban emissions by 23–26%. Green infrastructure, such as urban forests, lakes, and other natural features, can reduce emissions directly and indirectly, such as by lowering energy use for cooling.

In 2019, buildings produced 21% of global GHG emissions. Up to 80–90% of these emissions can be reduced while also helping achieve other Sustainable Development Goals. The report introduces a new method for reducing building emissions: SER, which stands for Sufficiency, Efficiency, and Renewable. Sufficiency measures do not require complex technology, energy supply, or maintenance. Examples include natural ventilation, green roofs, white walls, mixed-use spaces, and shared devices. Reducing building emissions is linked to the sharing economy and circular economy.

The IPCC found that decent living standards can be achieved with less energy use than previously thought. The report states that energy consumption needed for wellbeing is “between 20 and 50 gigajoules per person per year, depending on the situation.” More equal income distribution can lower emissions. Mitigation strategies that focus on reducing demand and increasing efficiency can provide decent living standards for all. Strategies based on reducing consumption and sustainable development have fewer negative effects than strategies focused on high consumption and limited mitigation. According to Table TS30, limited mitigation could increase habitat loss by 600%, but avoid habitat degradation by about 95%. Mitigation combined with sustainable development did not harm forest cover or biodiversity.

The report notes some progress in global climate action. For example, the rate of deforestation slowed after 2010, and total forest cover has increased in recent years due to reforestation efforts in Europe, Asia, and North America.

Reactions to all three working group reports

The Working Group 1 report was published in 2021 during the Northern Hemisphere summer, a time when many extreme weather events occurred. These included a heat wave in Western North America, flooding in Europe, heavy rainfall in India and China, and wildfires in multiple countries. Some scientists say these events show problems with the models used to create the report, as real-world experiences have shown more severe impacts than what scientific consensus predicted.

After the report was released, EU Vice President Frans Timmermans said it is not too late to stop runaway climate change. UK Prime Minister Boris Johnson stated that the next ten years will be critical for the planet's future.

Rick Spinrad, head of the US National Oceanic and Atmospheric Administration, said his agency will use new information from the IPCC report to help communities prepare for, respond to, and adapt to climate change.

John Kerry, the US special presidential envoy for climate, said the Working Group 2 report shows an increase in extreme weather events caused by climate change, which leave behind loss of life and destruction of livelihoods. He said the question now is not whether the crisis can be avoided completely, but whether the worst effects can be prevented.

Greta Thunberg, a Swedish climate activist, said the Working Group 1 report confirms what many studies have already shown: that the world is in an emergency.

Inger Andersen, an environmentalist, said, "Nature can be our savior, but only if we protect it first."

In a major article, The Guardian described the Working Group 1 report as the "starkest warning yet" about unavoidable and irreversible climate changes. This message was repeated by many media outlets after the report was released.

The Working Group 3 report found no evidence that sustainable development requires fossil fuels. Climate journalist Amy Westervelt said this finding challenges a common belief that fossil fuels are necessary for development.

UN Secretary-General António Guterres called the Working Group 1 report a "code red for humanity." He described the Working Group 2 report as "an atlas of human suffering" and criticized leaders for failing to act on climate change. He said the report also showed a list of broken climate promises by policymakers and urged more action, stating that countries increasing fossil fuel production are the real "dangerous radicals."

Synthesis report for all three working group reports

The synthesis report, which summarizes the entire document, was finalized during the 58th meeting of the panel in Interlaken, Switzerland, in March 2023. It was published on March 20, 2023. The report includes a summary for policymakers and was used as the foundation for the 2023 United Nations Climate Change Conference (COP28) in Dubai.

The report provides guidelines for both short-term and long-term actions. According to the report, the primary cause of the increase in global warming is the rise in carbon dioxide (CO2) emissions. It states that it is likely or very likely that global warming will exceed 1.5°C under higher emission scenarios.

The panel also released a detailed report, a summary for policymakers, a presentation, and a short document called "Headline Statements." Some key points from these statements include:

• "Human activities, mainly through the release of greenhouse gases, have clearly caused global warming. The average global surface temperature was 1.1°C higher than the 1850–1900 period during 2011–2020. Greenhouse gas emissions have continued to rise, with uneven contributions from different regions, countries, and individuals due to unsustainable energy use, land use changes, and consumption patterns."
• "Ongoing greenhouse gas emissions will lead to more global warming. The best estimate is that global warming could reach 1.5°C in the near future under certain scenarios. Each increase in global warming will make multiple dangers worse (high confidence). Making deep, rapid, and long-term cuts in greenhouse gas emissions could slow global warming within about two decades and change the atmosphere within a few years (high confidence)."
• "Climate change poses a serious threat to human health and the environment (very high confidence). There is a limited time left to create a livable and sustainable future for everyone (very high confidence)."

Society and culture

During the creation of the three main AR6 reports, a small group of scientists shared some information about the findings of Working Group III (Mitigation of Climate Change) through the group Scientist Rebellion. Governments have the ability to change the summaries for policymakers (SPM) in IPCC reports, which led the scientists to worry that politicians might weaken the details in the summary. According to the leaked information, human activities must reduce greenhouse gas (GHG) emissions by half by 2030 and fully eliminate them by 2050 to limit warming to 1.5 °C (2.7 °F). Achieving these goals would require major changes in daily life and economic systems.

Like other major international scientific efforts, the IPCC has faced criticism for not including enough scholars from the Global South. For example, some aspects of the process may prevent African scholars from participating, such as rules about publishing research and requiring individuals to be expert reviewers before joining the group of contributors.