IPCC Sixth Assessment Report
The Sixth Assessment Report of the United Nations Intergovernmental Panel on Climate Change is the sixth in a series of reports which assess the available scientific information on climate change. Three Working Groups covered the following topics: The Physical Science Basis ; [|Impacts, Adaptation and Vulnerability] ; [|Mitigation of Climate Change]. Of these, the first study was published in 2021, the second report February 2022, and the third in April 2022. The final synthesis report was finished in March 2023. It includes a summary for policymakers and was the basis for the 2023 United Nations Climate Change Conference in Dubai.
The first of the three working groups published its report on 9 August 2021, Climate Change 2021: The Physical Science Basis. A total of 234 scientists from 66 countries contributed to this first working group report. The authors built on more than 14,000 scientific papers to produce a 3,949-page report, which was then approved by 195 governments. The Summary for Policymakers document was drafted by scientists and agreed to line-by-line by the 195 governments in the IPCC during the five days leading up to 6 August 2021.
In the report, there are guidelines for both responses in the near term and in the long-term. According to the report, the main source of the increase in global warming is due to the increase in emissions, stating that it is likely or very likely to exceed 1.5 °C under higher emission scenarios.
According to the WGI report, it is only possible to avoid warming of or if massive and immediate cuts in greenhouse gas emissions are made. The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes", a theme echoed by many newspapers as well as political leaders and activists around the world.
Production
In April 2016, at the 43rd session which took place in Nairobi, Kenya, the topics for three Special Reports and one methodology report on Greenhouse Gases inventories in the AR6 assessment cycle were decided. These reports were completed in the interim phase since the finalisation of the Fifth Assessment Report and the publication of results from the Sixth Assessment Report.Structure
The sixth assessment report is made up of the reports of three working groups and a synthesis report which concluded the assessment in early 2023.- The Physical Science Basis of Climate Change in August 2021
- Impacts, Adaptation and Vulnerability in February 2022
- Mitigation of Climate Change in April 2022
- Synthesis Report in March 2023
Geopolitics
Those pathways assume that international cooperation and worldwide increase in GDP will facilitate adaptation to climate change. The geopolitical pathways served as one of the sources for the formation of the Shared Socioeconomic Pathways in the report among with other sources. One of the assumptions is that enough GDP and technology derived from fossil fuels development will permit to adapt even to temperature rise. Some experts assume, that while the odds for a worst-case scenario and the best base-case today seem lower, the most plausible outcome is around.
Special reports during same assessment cycle
Sequence of release dates of special IPCC reports during the same assessment cycle:- Special Report on Global Warming of 1.5 °C 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 in August 2019
- Special Report on the Ocean and Cryosphere in a Changing Climate in September 2019
Working Group 1 report (physical science basis)
According to the report, it is only possible to avoid warming of 1.5 °C or 2 °C if massive and immediate cuts in greenhouse gas emissions are made. In a front-page story, The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes", a theme echoed by many newspapers around the world.
The Technical Summary provides a level of detail between the Summary for Policymakers and the full report. In addition, an interactive atlas was made "for a flexible spatial and temporal analysis of both data-driven climate change information and assessment findings in the report".
Important findings of WG 1 report
The Working Group 1 report, Climate Change 2021: The Physical Science Basis comprises thirteen chapters and is focused on the foundational consensus of the climate science behind the causes and effects of human greenhouse gas emissions. Compared with previous assessments, the report included much more detail on the regional effects of climate change, although more research is needed on climate change in eastern and central North America. Sea-level rise by 2100 is likely to be from half to one metre, but two to five metres is not ruled out, as ice sheet instability processes are still poorly understood.The report quantifies climate sensitivity as between and for each doubling of carbon dioxide in the atmosphere, while the best estimate is 3 °C. In all the represented Shared Socioeconomic Pathways the temperature reaches the 1.5 °C warming limit, at least for some period of time in the middle of the 21st century. However, Joeri Rogelj, director of the Grantham Institute and a lead IPCC author, said that it is possible to completely avoid warming of 1.5 °C, but to achieve that the world would need to cut emissions by 50% by the year 2030 and by 100% by the year 2050. If the world does not begin to drastically cut emissions by the time of the next report of the IPCC, then it will no longer be possible to prevent 1.5 °C of warming. SSP1-1.9 is a new pathway with a rather low radiative forcing of 1.9 W/m2 in 2100 to model how people could keep warming below the 1.5 °C threshold. But, even in this scenario, the global temperature peaks at 1.6 °C in the years 2041–2060 and declines after.
According to AR6 coauthors, the probable temperature rise is in the middle of the scenario spectrum that ranges from 1.5 °C to 5 °C, at about 3 °C at the end of the century. It is likely that 1.5 °C will be reached before 2040. The threats from compound impacts are rated higher than in previous IPCC reports. The famous hockey stick graph has been extended.
Extreme weather is expected to increase in line with temperature, and compound effects may impact more on society. The report includes a major change from previous IPCC in the ability of scientists to attribute specific extreme weather events.
The global carbon budget to keep below 1.5 °C is estimated at 500 billion more tonnes of greenhouse gas, which would need the whole world to be net zero before 2050. Staying within this budget, if counting from the beginning of the year 2020, gives a 50% chance to stay below 1.5 °C. For having a 67% chance, the budget is 400 billion tonnes and for an 83% chance it is 300 billion tonnes. The report says that rapidly reducing methane emissions is very important, to make short-term gains to buy time for carbon dioxide emission cuts to take effect.
Any future warming will increase the occurrence of extreme weather events. Even in a 1.5 °C temperature rise there will be "an increasing occurrence of some extreme events unprecedented in the observational record". The likelihood of more rare events increases more.
The frequency, and the intensity of such events will considerably increase with warming, as described in the following table:
| Name of event | Climate in 1850–1900 | 1 °C warming | 1.5 °C warming | 2 °C warming | 4 °C warming |
| 1 in 10 years heatwave | Normal | 2.8 times more often, 1.2 °C hotter | 4.1 times more often, 1.9 °C hotter | 5.6 times more often, 2.6 °C hotter | 9.4 times more often, 5.1 °C hotter |
| 1 in 50 years heatwave | Normal | 4.8 times more often, 1.2 °C hotter | 8.6 times more often, 2.0 °C hotter | 13.9 times more often, 2.7 °C hotter | 39.2 times more often, 5.3 °C hotter |
| 1 in 10 years heavy precipitation event | Normal | 1.3 times more often, 6.7% wetter | 1.5 times more often, 10.5% wetter | 1.7 times more often, 14.0% wetter | 2.7 times more often, 30.2% wetter |
| 1 in 10 years drought | Normal | 1.7 times more often, 0.3 sd drier | 2.0 times more often, 0.5 sd drier | 2.4 times more often, 0.6 sd drier | 4.1 times more often, 1.0 sd drier |
Working Group 2 report (impacts, adaptation and vulnerability)
The second part of the report, a contribution of working group II, was published on 28 February 2022. Entitled Climate Change 2022: Impacts, Adaptation & Vulnerability, the full report is 3675 pages, plus a 37-page summary for policymakers. It contains information on the impacts of climate change on nature and human activity. Topics examined included biodiversity loss, migration, risks to urban and rural activities, human health, food security, water scarcity, and energy. It also assesses ways to address these risks and highlights how climate resilient development can be part of a larger shift towards sustainability.The report was published during the first week of the 2022 Russian invasion of Ukraine. In the context of the conflict, the Ukrainian delegation connected the Russian aggression to the global dependency on oil, and a Russian official, Oleg Anisimov, apologized for the conflict despite the possible repercussions. The Ukrainian delegation also called for news reporting on the war not to overshadow the WGII report.