IPCC Sixth Assessment Report

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The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports which assess scientific, technical, and socio-economic information concerning climate change. Three Working Groups (WG) assess

  • I The Physical Science Basis,
  • II Impacts, Adaptation and Vulnerability and
  • III Mitigation of Climate Change,

of which the first WGI study has been published in 2021 and the other two are planned for 2022. The final synthesis report is due to be finished by late 2022.

The first of three working groups (WGI) published Climate Change 2021: The Physical Science Basis on 9 August 2021.[1][2] A total of 234 scientists from 66 countries contributed to this first of three working group reports.[3][4] The report's authors[5] built on more than 14,000 scientific papers to produce a 3,949-page report, which was then approved by 195 governments.[6] The Summary for Policymakers (SPM) 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.[5]

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.[1] In a front page story, The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes",[7] a theme echoed by many newspapers[8] as well as political leaders and activists around the world.

Production[]

History[]

After the IPCC had been founded in 1988, the First Assessment Report was published in 1990 and received an Update in 1992.[9] In intervals of about 6 years, new editions of IPCC Assessment Report followed: AR2 in 1995, AR3 in 2001, AR4 in 2007, and AR5 in 2014.

In April 2016, at the 43rd session which took place in Nairobi, Kenya, the topics for three Special Reports (SR) and one methodology report on GHG inventories in the AR6 assessment cycle were decided.[10][11] 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.

Sequence of release dates:

Structure[]

The sixth assessment report is made up of the reports of three working groups (WG I, II, and III) and a synthesis report which concludes the assessment in late 2022.[2]

  • The Physical Science Basis of Climate Change in August 2021[12][13] (WGI contribution)
  • Impacts, adaptation and vulnerability in February 2022 (WGII contribution)
  • Mitigation of climate change in March 2022 (WGIII contribution)
  • Synthesis Report in October 2022[14]

Leaks[]

During the preparation of the three main AR6 reports, a small group of scientists leaked some information on the results of Working Group III (Mitigation of Climate Change) through the organization Scientists Rebellion. As governments can change the summaries for policymakers (SPM) for IPCC reports, the scientists were afraid that politicians might dilute this information in the summary. According to the leaked information, humanity should cut GHG emissions by 50% by 2030 and completely by 2050 in order to limit warming to 1.5 °C. These efforts require strong changes in lifestyle and economy.[15][16]

Geopolitics[]

Geopolitics has been 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 have been published in 2016.

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.[17]: 1-98ff  One of the assumptions is that enough GDP and technology derived from fossil fuels development will permit to adapt even to 5 °C temperature rise. However, the report that is based on consensus science and was written by hundreds of scientists did not confirm the assumption about adaptation to 5 °C. Some experts assume, that while the odds for a worst case scenario (5 ºC) and the best base-case (1.5 ºC) today seem lower, the most plausible outcome is something in between (ca. 3 °C).[18]

The report explicitly says: "Each pathway is an internally consistent, plausible and integrated description of a socio-economic future, but these socio-economic futures do not account for the effects of climate change, and no new climate policies are assumed. [..] By design, the evolution of drivers and emissions within the SSP scenarios do not take into account the effects of climate change."[17]: 1–100 

Participation[]

Like other major international scientific processes, the IPCC has been accused of not sufficiently including scholars from the Global South. For example, the biases were highlighted that prevent African scholars from participating, such as publication requirements and being an expert reviewer before joining the panel of contributors.[19] Similarly, the physical sciences report only had 28% women in its team of authors.[20]

The Physical Science Basis[]

Variation of annual observed global average temperature (1850–2019) relative to the 1850–1900 average (blue line), as reported in the Summary for Policymakers (SPM)[21]

A total of 234 scientists from 66 countries contributed to the first of three working group reports.[3][4] Working group 1 (WGI) published Climate Change 2021: The Physical Science Basis.[1][2] The report's authors[5] built on more than 14,000 scientific papers to produce a 3,949-page report, which was then approved by 195 governments.[6] The Summary for Policymakers (SPM) 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.[5] It was published on Monday, 9 August 2021.

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.[1] In a front page story, The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes",[7] a theme echoed by many newspapers around the world.[8]

The Technical Summary (TS) provides a level of detail between the Summary for Policymakers (SPM) 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."[22] Following IPCC protocol adopted in May 2011, errata were and are being compiled. Thirty-four (34) questions were published as part of the FAQs section, with each one related to a chapter of the report. Regional fact sheets were made available for geographic regions of the globe, drawing on facts from the reports. The data for the SPM are being held and visible at the UK Centre for Environmental Data Analysis website. Computer slides were made available as part of the "Outreach Materials" , for press conferences and basic presentations.

Findings[]

The Working Group 1 (WGI) 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,[6] although more research is needed on climate change in eastern and central North America.[23] 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.[23]

The report quantifies climate sensitivity as between 2.5 °C and 4 °C for each doubling of carbon dioxide in the atmosphere,[6] while the best estimate is 3 °C.[24]: SPM-14  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,  [de], 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.[25] 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.[23]

Shared Socioeconomic Pathways in the IPCC Sixth Assessment Report [26]
  • v
  • t
SSP Scenario
(Likelihood [27])		 Estimated warming
(2041–2060)		 Estimated warming
(2081–2100)		 Very likely range in °C
(2081–2100)
SSP1-1.9 very low GHG emissions:
CO2 emissions cut to net zero around 2050 		1.6 °C 1.4 °C 1.0 – 1.8
SSP1-2.6 low GHG emissions:
CO2 emissions cut to net zero around 2075 		1.7 °C 1.8 °C 1.3 – 2.4
SSP2-4.5 intermediate GHG emissions (likely):
CO2 emissions around current levels until 2050, then falling but not reaching net zero by 2100 		2.0 °C 2.7 °C 2.1 – 3.5
SSP3-7.0 high GHG emissions (unlikely):
CO2 emissions double by 2100 		2.1 °C 3.6 °C 2.8 – 4.6
SSP5-8.5 very high GHG emissions (highly unlikely):
CO2 emissions triple by 2075 		2.4 °C 4.4 °C 3.3 – 5.7

According to AR6 coauthors, the probable temperature rise is in the middle of the scenario spectrum that reaches from 1.5 °C to 5 °C, at about 3 °C at the end of the century.[18] It is likely that 1.5 °C will be reached before 2040.[23] The threats from compound impacts are rated higher than in previous IPCC reports.[23] The famous hockey stick graph has been extended.[23]

Extreme weather is expected to increase in line with temperature, and compound effects (such as heat and drought together) may impact more on society.[23] The report includes a major change from previous IPCC in the ability of scientists to attribute specific extreme weather events.[28]

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.[5] 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 a 83% chance it is 300 billion tonnes.[24]: SPM-38f  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.[5]

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.[24]: SPM-19 

The frequency, and the intensity of such events will considerably increase with warming, as described in the following table:[24]: SPM-23 

Increase in frequency and intensity of extreme events with global warming
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
Increase in frequency of extreme events with global warming in the Sixth Assessment Report's Summary for Policymakers[29]

Reception[]

The report is expected to influence the 2021 United Nations Climate Change Conference in early November.[5]

In science[]

The publication of the report was during the Northern Hemisphere summer, where there was much extreme weather, such as a Western North America heat wave, flooding in Europe, extreme rainfall in India and China, and wildfires in several countries.[3][30] Some scientists are describing these extreme weather events as clear gaps in the models used for writing the report, with the lived experience proving more severe than the consensus science.[30][31]

In politics[]

After publication of the Working Group 1 report, EU Vice President Frans Timmermans said that it is not too late to prevent runaway climate change.[32] UK Prime Minister Boris Johnson said that the next decade will be pivotal to the future of the planet.[33]

Rick Spinrad, administrator of the US's National Oceanic and Atmospheric Administration, stated that his agency "will use the new insights from this IPCC report to inform the work it does with communities to prepare for, respond to, and adapt to climate change".[34]

NGO[]

Swedish climate activist Greta Thunberg said that the report "confirms what we already know from thousands [of] previous studies and reports—that we are in an emergency".[35]

In media[]

In a front page story, dedicated to the report The Guardian described it as "starkest warning yet" of "major inevitable and irreversible climate changes".[7] This message was echoed by many media channels after the release of the report.[8]

According to CTXT, the publication that first posted the leaked materials from the report: "it showed that the global economy must be shifted rapidly away from a reliance on conventional GDP growth, but that the report underplays this."[36][37]

From the United Nations[]

The Secretary-General of the UN, António Guterres, called the report a "code red for humanity".[38]

References[]

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Further reading[]

External links[]

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