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 examine scientific information about climate change. Three Working Groups (WGI, II, and III) focused on these topics: The Physical Science Basis (WGI); Impacts, Adaptation and Vulnerability (WGII); Mitigation of Climate Change (WGIII). The first study was published in 2021, the second in February 2022, and the third in April 2022. A final synthesis report was completed in March 2023. This report includes 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 published its report on August 9, 2021, titled Climate Change 2021: The Physical Science Basis. A total of 234 scientists from 66 countries helped create this report. The authors used more than 14,000 scientific papers to write a 3,949-page report, which was approved by 195 governments. The Summary for Policymakers (SPM) was written by scientists and agreed to line-by-line by the 195 governments during five days before August 6, 2021.

The report provides guidelines for both short-term and long-term responses to climate change. It states that the main cause of increased global warming is the rise in carbon dioxide (CO₂) emissions, and it is likely or very likely that warming will exceed 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 inevitable and irreversible climate changes," a message supported by many newspapers, political leaders, and activists worldwide.

Production

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

The Sixth Assessment Report includes the reports of three working groups (WG I, II, and III) and a synthesis report that concluded the assessment in early 2023.

• 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

Geopolitical factors were included in climate models for the first time, in the form of five Shared Socioeconomic Pathways: SSP1 "Taking the Green Road," SSP2 "Middle of the Road," SSP3 "A Rocky Road," SSP4 "A Road Divided," and SSP5 "Taking the Highway," which were published in 2016.

These pathways assume that international cooperation and worldwide increases 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 adaptation 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).

Sequence of release dates for special IPCC reports during the same assessment cycle:

• 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 a report titled Climate Change 2021: The Physical Science Basis. The report's authors used more than 14,000 scientific papers to write 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. The SPM was published on Monday, 9 August 2021.

The report states that avoiding warming of 1.5 °C or 2 °C is only possible if large and quick reductions in greenhouse gas emissions are made. A news story in The Guardian called the report "its starkest warning yet" about "major and unavoidable climate changes." This idea was repeated by many newspapers worldwide.

The Technical Summary (TS) includes details between the Summary for Policymakers (SPM) and the full report. An interactive atlas was created to help analyze climate change data and findings in the report.

The WGI report, Climate Change 2021: The Physical Science Basis, has thirteen chapters and focuses on the scientific agreement about the causes and effects of human greenhouse gas emissions. Compared to earlier reports, this one includes more information about regional climate changes, though more research is needed about climate changes 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 cannot be ruled out because processes related to ice sheet instability are not fully understood.

The report states that climate sensitivity is between 2.5 °C (4.5 °F) and 4.0 °C (7.2 °F) for each doubling of carbon dioxide in the atmosphere, with the best estimate at 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, director of the Grantham Institute and an IPCC lead author, said it is possible to completely avoid 1.5 °C of warming if the world cuts emissions by 50% by 2030 and by 100% by 2050. If the world does not begin reducing emissions significantly before the next IPCC report, it will no longer be possible to prevent 1.5 °C of warming. SSP1-1.9 is a new pathway that models how people might keep warming below 1.5 °C. In this scenario, global temperatures peak at 1.6 °C between 2041 and 2060 and then decline.

The IPCC Sixth Assessment Report did not estimate the likelihoods of the 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, with a range of 2.3–3.0 °C. Including uncertainties, the range expands to roughly 1.9–3.7 °C. The paper also states that current emissions pathways align most closely with or slightly fall below SSP2-4.5 rather than SSP3-7.0.

According to AR6 coauthors, the likely temperature rise is in the middle of the scenario range from 1.5 °C to 5 °C, with about 3 °C by the end of the century. It is likely that 1.5 °C of warming will be reached before 2040. The report rates threats from combined effects of extreme weather as higher than in previous IPCC reports. The famous "hockey stick" graph has been updated.

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

The global carbon budget to stay below 1.5 °C is estimated at 500 billion additional tonnes of greenhouse gas emissions. To stay within this budget, the world must reach net zero emissions before 2050. If counting from the start of 2020, there is a 50% chance of staying below 1.5 °C. 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 rapidly reducing methane emissions to buy time for carbon dioxide cuts to take effect.

Any future warming will increase the frequency and intensity of extreme weather events. Even with 1.5 °C of warming, some extreme events will become more common than ever recorded. The likelihood of rare events will increase further.

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 published 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 explains how climate change affects nature and human activities. It covers topics such as loss of plant and animal life, movement of people, risks to cities and rural areas, human health, food supplies, water shortages, and energy use. It also discusses ways to reduce these risks and shows how building resilience to climate change can help move toward a more sustainable future.

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

The report found that climate change effects are more severe than earlier estimates, and all parts of the world are affected. At least 3.3 billion people, or about 40% of the global population, are now in the most serious category of "highly vulnerable." The worst effects are seen in developing countries. If emissions continue as they are, Africa could lose 30% of its land used for growing maize and 50% of its land used for growing beans. One billion people may face flooding from rising sea levels. Climate change also increases the risk of disease outbreaks, such as the COVID-19 pandemic. The report also states that China will face the highest financial costs if temperatures rise further. These costs include food shortages, water shortages, flooding, especially in coastal areas, and stronger storms. In some parts of China, temperatures may rise to levels humans and other mammals cannot tolerate for more than six hours. Overall, the report lists 127 negative impacts of climate change, some of which cannot be reversed.

People can reduce the effects of climate change through actions called adaptation. Progress in adaptation has been made in many areas, but it is uneven. Many efforts focus on immediate risks rather than long-term changes. However, many adaptation actions are effective and can help achieve goals like improving health and reducing poverty. For example, most current adaptations address water-related risks. Actions like better water management, storage, and irrigation reduce vulnerability and can also provide economic and environmental benefits. Similarly, actions like planting trees with crops, diversifying farms, and growing food in cities can increase food supplies while improving sustainability.

The report emphasizes the need to protect nature to preserve biodiversity and reduce climate change effects. It states that protecting about 30% to 50% of Earth’s land, water, and ocean areas is needed to keep ecosystems strong. The report criticizes some technological methods to remove carbon dioxide from the air and suggests that urban planning can help reduce emissions by promoting public transport and renewable energy. It also warns that methods like controlling sunlight to cool the planet, planting forests in unsuitable areas, or using certain types of bioenergy may carry serious risks.

The report also discusses "loss and damage," which refers to the effects of climate change that cannot be avoided even with adaptation. These effects are already happening, such as more frequent droughts, floods, and heatwaves, and a major loss of plant and animal life. Taking steps now to limit warming to below 1.5°C could reduce future harm, but not all damage can be stopped. Wealthier countries have previously avoided taking responsibility for these losses.

The report explains that even a short period of exceeding the 1.5°C warming limit will harm people and ecosystems. Some effects may release more greenhouse gases and cannot be reversed, even if warming is later reduced. Building resilience to climate change will be harder if global temperatures rise by 1.5°C above pre-industrial levels. If temperatures rise by more than 2°C, it may become impossible to adapt in some areas.

Although the report’s findings are serious, it concludes that it is still possible to limit warming to 1.5°C by greatly reducing greenhouse gas emissions immediately. Climate resilience efforts can help both reduce risks and cut emissions, but they require global teamwork and partnerships with 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 conclusions may be made less strong because of how the report is approved. According to The Observer, some countries "have tried to change the report to weaken the final warnings."

The report includes new methods, such as involving different groups like young people, indigenous communities, cities, and businesses in solving climate problems. It states, "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 much stronger than it is now. Many developing countries need more support from other countries to take strong climate action.

According to the report, demand-side mitigation measures can reduce greenhouse gas emissions by 40 to 70% by the year 2050 compared to scenarios where countries only meet their previous climate pledges. For these measures to be successful, they must be linked to improving basic well-being for all people.

The report concludes that achieving net zero emissions requires using carbon dioxide removal technologies. It states, "All global pathways that limit warming to 1.5 °C… with no or limited overshoot, and those that limit warming to 2 °C… involve rapid and deep, and in most cases immediate, greenhouse gas emission reductions in all sectors." These reductions can be achieved through strategies like switching from fossil fuels without carbon capture and storage to low- or zero-carbon energy sources, such as renewables or fossil fuels with carbon capture and storage, demand-side measures, improving efficiency, reducing non-CO₂ emissions, and using carbon dioxide removal (CDR) methods to balance remaining emissions. The report compares different CDR methods, including agroforestry, reforestation, blue carbon management, and peatland restoration.

Cities have the potential to greatly reduce greenhouse gas emissions. With full-scale mitigation action, city emissions could be reduced to near zero, with the worst-case scenario allowing a small remaining amount of 3 gigatons of CO₂-equivalent. Planning cities to support mixed-use spaces, public transit, walking, cycling, and shared vehicles can reduce urban emissions by 23 to 26%. Green spaces like urban forests, lakes, and other blue and green infrastructure can directly and indirectly reduce emissions, such as by lowering energy needs for cooling.

Buildings produced 21% of global greenhouse gas emissions in 2019. Up to 80 to 90% of these emissions can be reduced while helping achieve other Sustainable Development Goals. The report introduces a new method for reducing emissions in buildings: SER = Sufficiency, Efficiency, Renewable. Sufficiency measures do not require complex technology, energy supply, maintenance, or replacement during a building’s lifetime. Examples include natural ventilation, green roofs, white walls, mixed-use spaces, and shared use of devices. Reducing emissions from buildings is connected to the sharing economy and circular economy.

The IPCC found that decent living standards can be achieved using less energy than previously thought. The report states that the energy needed for well-being 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 low energy use and high efficiency can achieve good living standards for all. Strategies that reduce consumption and promote sustainable development have fewer negative effects than strategies based on high consumption and limited mitigation. According to Table TS30, limited mitigation can increase habitat loss by 600% but avoid habitat degradation by about 95%. Mitigation with sustainable development does not harm forest cover or biodiversity.

The report notes some improvements 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 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 several countries. Some scientists say these events show problems with the models used to write the report, as real-world experiences have been more severe than what scientists predicted.

After the report was published, EU Vice President Frans Timmermans said it is not too late to stop climate change from getting out of control. UK Prime Minister Boris Johnson stated that the next ten years will be very important for the planet's future.

Rick Spinrad, who leads 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 lost lives and ruined 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 that nature can help save the planet, but only if people protect it first.

A front-page article in The Guardian called the Working Group 1 report the "starkest warning yet" about major, unavoidable, and permanent climate changes. This message was repeated by many news outlets after the report was released.

The Working Group 3 report found no evidence that sustainable development needs fossil fuels. Climate journalist Amy Westervelt said this finding is one of the most important in the report, as it challenges the idea that fossil fuels are necessary for development.

António Guterres, the UN Secretary-General, called the Working Group 1 report a "code red for humanity." He said the Working Group 2 report is "an atlas of human suffering" and criticized leaders for failing to address climate change. He added that the Working Group 3 report highlights a list of broken climate promises by policymakers and urged more action. He also said that climate activists are sometimes called dangerous radicals, but he believes the real danger comes from countries that increase fossil fuel production.

Synthesis report for all three working group reports

A summary report that explains the entire document was completed during the 58th meeting of the panel in Interlaken in March 2023. It was published on 20 March 2023 and includes a summary for policymakers. This report served as the foundation for the 2023 United Nations Climate Change Conference (COP28) in Dubai.

The report provides guidelines for addressing climate change in both the short and long term. It states that the primary cause of increased global warming is the rise in carbon dioxide (CO₂) emissions. It is likely or very likely that global temperatures will exceed 1.5°C above pre-industrial levels under higher emission scenarios.

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

• "Human activities, mainly through greenhouse gas emissions, have clearly caused global warming. Global surface temperatures were 1.1°C higher than levels from 1850–1900 during 2011–2020. Greenhouse gas emissions continue to rise, with uneven contributions from unsustainable energy use, land use changes, lifestyles, and consumption patterns across regions, countries, and individuals."

• "Ongoing greenhouse gas emissions will increase global warming. The best estimate suggests that 1.5°C of warming could occur soon in scenarios studied by scientists. Each increase in global warming will worsen multiple dangers (high confidence). Large, quick, and lasting reductions in greenhouse gas emissions could slow global warming within about two decades and change the atmosphere’s composition within a few years (high confidence)."

• "Climate change threatens human well-being and the health of the planet (very high confidence). There is a rapidly closing opportunity to create a livable and sustainable future for all (very high confidence)."

Society and culture

During the creation of the three main AR6 reports, a small group of scientists shared some details about the findings of Working Group III (Mitigation of Climate Change) through an organization called Scientist Rebellion. Governments have the ability to change the Summary for Policymakers (SPM) sections of IPCC reports, and the scientists were worried that politicians might weaken the information in these summaries. According to the shared information, to limit warming to 1.5 °C (2.7 °F), human activities must reduce greenhouse gas (GHG) emissions by half by 2030 and completely eliminate them by 2050. These changes would require major shifts in daily life and economic systems.

Like other large international scientific processes, the IPCC has been criticized for not involving enough scientists from the Global South. For example, some rules in the process, such as requirements for publishing research and needing to be an expert reviewer before joining the group of contributors, may make it harder for African scientists to participate.