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IPCC Sixth Assessment Report

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Intergovernmental Panel on
Climate Change
IPCC Assessment Reports
IPCC Special Reports

The Sixth Assessment Report (AR6) of the United Nations Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports intended to assess scientific, technical, and socio-economic information concerning climate change. 234 scientists contributed to the final report.[1]

Working group 1 published The Physical Science Basis of Climate Change on 9 August 2021, which said that, if greenhouse gas emissions are halved by 2030 and net zero by 2050, global warming can be stopped.[2] The report's 234 authors[3] built on more than 14,000 scientific papers to produce a 3,949 page report, which was then approved by 195 governments.[4] The summary for policymakers was drafted by scientists and agreed to line-by-line by governments during the 5 days leading up to 6 August 2021.[3]

Structure

The sixth report is made up of the reports of three working groups (WG) and a synthesis report. In April 2016, at the 43rd session in Nairobi, Kenya, the topics for Special Reports in the AR6 assessment cycle were decided.[5][6]

Sequence of release dates, actual and planned:

Content

The Physical Science Basis of Climate Change

Variation of observed global average temperature relative to the 1850–1900 average, as reported in the Summary for Policymakers

The Working Group 1 report, The Physical Science Basis of Climate Change, focused on the foundational consensus of the climate science on the causes and effects of human greenhouse gas emissions. It was published on 9 August 2021.

Compared with previous assessments, the report included much more detail on the regional effects of climate change,[10] although more research is needed on climate change in eastern and central North America.[11] 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.[11]

The report quantifies climate sensitivity as between 2.5 and 4 °C for each doubling of carbon dioxide in the atmosphere.[10] Geopolitics has been included in climate models for the first time, as five Shared Socioeconomic Pathways,[12] with SSP1-1.9 being a new pathway to model how people could keep warming below 1.5 °C.[11] The report narrows the range of probable temperature rise to between 1.5 °C and 5 °C,[12] with 1.5 °C likely to be reached before 2040.[11] The threats from compound impacts are rated higher than in previous IPCC reports.[11] The famous hockey stick graph has been extended.[11] Extreme weather is expected to increase in line with temperature and compound each other, making extreme weather events more impactful on society.[11]

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.[3] The report says that rapidly reducing methane emissions is very important.[3]

Climate impact

Below is the summary of impact and key points taken from the BBC report:[13]

Future impact

  • Temperatures will reach 1.5 °C above 1850–1900 levels by 2040 under all emissions scenarios
  • The Arctic is likely to be practically ice-free in September at least once before 2050 in all scenarios assessed
  • There will be an increasing occurrence of some extreme events "unprecedented in the historical record" even at warming of 1.5 °C
  • Extreme sea level events that occurred once a century in the recent past[specify] are projected to occur at least annually at more than half of tidal gauge locations by 2100
  • There will be likely increases in fire weather in many regions

Key points

  • Global surface temperature was 1.09 °C higher in the decade between 2011–2020 than between 1850–1900
  • The past five years have been the hottest on record since 1850
  • The recent[when?] rate of sea-level rise has nearly tripled compared with 1901–1971
  • Human influence is "very likely" (90%) the main driver of the global retreat of glaciers since the 1990s and the decrease in Arctic sea-ice
  • It is "virtually certain" that hot extremes including heatwaves have become more frequent and more intense since the 1950s, while cold events have become less frequent and less severe

Reception

The Working Group 1 report is expected to influence the 2021 United Nations Climate Change Conference.[3]

In science

The publication of the The Physical Science Basis of Climate Change was during the Northern Hemisphere summer, where there was a notable amount of extreme weather events such as a Western North America heat wave, flooding in Europe, extreme rainfall events in India and China, and other events such as wildfires.[1][14] Some scientists are describing these extreme weather events as leading to doubt of the rate of emergence of extreme events in the models used for writing the report, with the lived experience proving more severe than the consensus science.[14]

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.[15] UK Prime Minister Boris Johnson said that the next decade will be pivotal to the future of the planet.[16]

Rick Spinrad, administrator of the US's NOAA, 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".[17]

Climate activist Greta Thunberg pointed out that the report "confirms what we already know from thousands previous studies and reports—that we are in an emergency".[18]

United Nations

The Secretary-General of the UN, António Guterres, called the report a "code red for humanity".[19]

Further reading

References

  1. ^ a b "UN climate science talks open amid heatwaves, floods and drought". UN News. 26 July 2021. Retrieved 2 August 2021.
  2. ^ "Climate change: IPCC report is 'code red for humanity'". BBC News. 9 August 2021. Retrieved 9 August 2021.
  3. ^ a b c d e "The IPCC delivers its starkest warning about the world's climate". The Economist. 9 August 2021. ISSN 0013-0613. Retrieved 9 August 2021.
  4. ^ Plumer, Brad; Fountain, Henry (9 August 2021). "A Hotter Future Is Certain, Climate Panel Warns. But How Hot Is Up to Us". The New York Times. ISSN 0362-4331. Retrieved 9 August 2021.
  5. ^ ""Sixth Assessment Report"".
  6. ^ ""The IPCC and the sixth Assessment cycle"" (PDF).
  7. ^ ""Tentative IPCC AR6 WGI schedule for 2020-2021 (11 June 2020)"" (PDF).
  8. ^ "IPCC opens meeting to approve physical science report — IPCC". Retrieved 28 July 2021.
  9. ^ "IPCC reschedules report approval sessions — IPCC".
  10. ^ a b Plumer, Brad; Fountain, Henry (9 August 2021). "A Hotter Future Is Certain, Climate Panel Warns. But How Hot Is Up to Us". The New York Times. ISSN 0362-4331. Retrieved 9 August 2021.
  11. ^ a b c d e f g "Key takeaways from the new IPCC report » Yale Climate Connections". Yale Climate Connections. 9 August 2021. Retrieved 9 August 2021.
  12. ^ a b Coren, Michael J. "Scientists have finally added world politics to their climate models". Quartz. Retrieved 9 August 2021.
  13. ^ "Climate change: IPCC report is 'code red for humanity'". BBC News. 9 August 2021. Retrieved 10 August 2021.
  14. ^ a b "Commentary: We are living through a new, horrible phase of climate change". CNA. Retrieved 2 August 2021.
  15. ^ "'Not too late' to prevent 'runaway climate change': EU". WION. Retrieved 9 August 2021.
  16. ^ "World's 1.5C goal slipping beyond reach without urgent action, warns landmark UN climate report". The Independent. 9 August 2021. Retrieved 9 August 2021.
  17. ^ "Statement from NOAA Administrator Rick Spinrad on new IPCC report". National Oceanic and Atmospheric Administration. 9 August 2021. Retrieved 9 August 2021.{{cite web}}: CS1 maint: url-status (link)
  18. ^ Berry, Alex (9 August 2021). "IPCC report: World reacts to ominous climate warning". Deutsche Welle. Retrieved 10 August 2021.{{cite web}}: CS1 maint: url-status (link)
  19. ^ "Secretary-General's statement on the IPCC Working Group 1 Report on the Physical Science Basis of the Sixth Assessment". United Nations. Retrieved 9 August 2021.{{cite web}}: CS1 maint: url-status (link)
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