Freya Doughty

(Part I of II)

The Intergovernmental Panel on Climate Change (hereinafter ‘IPCC‘) released the first part of their Sixth Assessment Report, entitled ‘Climate Change 2021: The Physical Science Basis,’ on August 9th, 2021. Working Group I’s significant scholarly contribution is a successor to its marginally more hopeful Fifth Assessment Report published in 2013, and a partial continuation of the IPCC’s 2018-19 Special Reports. The Sixth Report in its entirety is 3,949 pages – let’s make it bite-sized (comparatively).

News outlets have been quick to report pessimistic, attention-grabbing headlines in their summaries of the IPCC’s paper. Repeated buzzwords include bleak, code-red, devastating, catastrophic, and irreparable. We have quickly transitioned from an inconvenient truth to a cataclysmic reality, something the IPCC has made overwhelmingly apparent in this publication.

Its report breaks matters down in to four main parts: the Current State of the Climate; Possible Climate Futures; Climate Information for Risk Assessment and Regional Adaptation; and Limiting Future Climate Change. The first section explores a variety of data collected, and gives a statistical overview. The second section examines five different climate possibilities for the period of 2081-2100. Parts three and four will be covered in the second blog post.

Current State of the Climate, part 1: This is Human Made

– Levels of carbon dioxide, methane, and nitrous oxide have all continued to increase in the atmosphere, as a direct result of human activities. The IPCC is ‘confident’ of this;
– Each of the last four decades has been warmer than the one prior. The global surface temperature was 1.09C higher in 2011-2022 than 1850-1900, with land warming more than the oceans;
– It is ‘very likely‘ greenhouse gases (GHGs) were the primary driver of tropospheric warming since 1979;
– The global retreat of glaciers since the 1990s and the decrease in the Arctic Sea Area is ‘very likely‘ thanks to human influence;
– Warming of the global upper ocean since the 1970s is ‘virtually certain,’ as is the global acidification of the open oceans both being a reality and caused by human influence;
– Global mean sea level increased by 0.20m between 1901 and 2018, going from 1.33mm/yr between 1901 and 1971 to 3.7mm/yr between 2006 and 2018.

– Lastly, it is ‘extremely likely’ that stratospheric ozone depletion was the main driver behind the cooling of the lower stratosphere between 1979 and the mid-1990s. Aerosols principally contributed to a cooling of 0.0C to 0.8C in this period.

Current State of the Climate, part 2: Warming and Environmental Destruction Rates are Unprecedented

– In 2019, atmospheric CO2 concentrations were higher than any time seen in the past 2 million years, and CH4 and N2O were higher that at any time in the past 800,000 years; (IPCC: ‘very high confidence,’)
– Global surface temperature has increased faster since 1970 than in any other 50-year period seen in the past 2,000 years; (IPCC: ‘high confidence,’)
– Between 2011 and 2020, annual Arctic sea ice area reached its lowest level since 1850; (IPCC: ‘high confidence,’)
– Global mean sea level has risen faster in the twentieth century than over any preceding century in the past 3,000 years. (IPCC: ‘high confidence.’)

Current State of the Climate, part 3: We are Already Experiencing the Extremes

– Hot extremes, including heatwaves, have become more frequent and more intense across most land regions since the 1950s, with cold extremes becoming less frequent and less severe; (IPCC: ‘virtually certain,’)
– Some extremes in particular would have been ‘extremely unlikely‘ to have occurred were it not for human influence. The increase of fire weather and compound flooding in some regions being caused by human influence is only regarded with ‘medium confidence;’
– The frequency and intensity of increased heavy precipitation events have increased since the 1950s, with human influence being the ‘likely’ main driver. Humans have also contributed to agricultural and ecological droughts. (IPCC: ‘medium confidence.’)

Current State of the Climate, part 4: Our Knowledge and Data are More Accurate

– Since the publication of the Fifth Assessment Report, the climate focused community has improved the accuracy of climate measuring systems and of paleoclimate evidence.

Possible Climate Futures, part 1: When All Potential Scenarios are Examined, Global Surface Temperature Increase is Inevitable

– Compared to 1850-1900, global surface temperature averaged over 2081-2100 is ‘very likely‘ to be higher by 1.0C-1.8C when GHGs remain low. 2.0C+ warming will occur if GHGs are not considerably reduced. The IPCC has ‘medium confidence‘ that the last time temperatures 2.5C higher than the 1850-1900 period were sustained was 3 million years ago;
– Based on the five above scenarios, global warming of 2.0C is a certainty in SSP3-7.0 and SSP5-8.5. In SSP2-4.5, warming of 2.0C is ‘extremely likely.‘ However, in the very low and low GHG emission scenarios, warming of 2.0C is ‘extremely unlikely‘ and ‘unlikely‘ to be exceeded respectively;
– Global warming of 1.5C relative to 1850-1900 in the near term (2021-2040) is only ‘more likely than not‘ to be reached in the lowest GHG scenario. Further, it is ‘more likely than not‘ that the global surface temperature would decrease back to below 1.5C in the 21st century.

Possible Climate Futures, part 2: Climate System Changes are Increasingly Becoming a Direct Result of Anthropogenic Global Warming

– It is ‘virtually certain,’ that land temperatures will increase more than ocean temperatures;
– The Arctic will warm more than the global surface temperature with ‘virtual certainty,’ and at two times the rate of global warming; (latter statement: ‘high confidence,’)
– With each temperature increase of 0.5C, weather extremes will become more significant. This includes heatwaves (‘very likely‘), heavy precipitation (‘high confidence‘), and agricultural and ecological droughts (‘high confidence‘);
– Some mid-latitude and semi-arid regions, and the South American Monsoon region, are projected to see a temperature increase on its hottest days of 1.5-2x the rate of global warming; (IPCC: ‘high confidence,‘)
– The Arctic is predicted to see the highest temperature increase on its coldest days, 3x the rate of global warming; (IPCC: ‘high confidence,’)
– At the global scale, extreme daily precipitation events are projected to intensify by 7% for each 1.0C increase in global temperature; (IPCC: ‘high confidence,’)
– The Arctic is ‘likely’ to be practically sea ice free in September at least once by 2050, with rates increasing in the higher proportion of GHG scenarios;
– There is ‘low confidence’ in the projected decrease of Antarctic sea ice.

Possible Climate Futures, part 3: Global Warming Will Intensify the Global Water Cycle

– The average annual global land precipitation is projected to ‘likely‘ increase by 0-5% under the low GHG emissions scenario, and 1-15% under the very high GHG emissions scenario;
– Precipitation is expected to increase over high latitudes, the equatorial Pacific, and part of the monsoon regions, but decrease over parts of the subtropics and and limited areas in the tropics in GHG scenarios 3-5; (IPCC: ‘very likely,’)
– A warmer climate will exacerbate very wet and very dry weather and seasons, increasing the chances of flooding and drought with ‘high confidence;‘
– Monsoon precipitation is projected to increase on a global scale, particularly over South and Southeast Asia, East Asia, and West Africa apart from the far west Sahel. (IPCC: ‘high confidence.’)

Possible Climate Futures, part 4: As CO2 Emissions Increase, Ocean and Land Carbon Sinks Will Be Less Effective

– Based on model projections, under the intermediate GHG scenario (SSP2-4.5), the rates of CO2 taken up by the land and oceans are projected to decrease in the second half of the 21st century; (IPCC: ‘high confidence,’)
– It is ‘very unlikely’ natural carbon sinks will turn into a source by 2100 under any scenario without negative net emissions;
– Additional ecosystem responses to warming not yet included in climate models, such as CO2 and CH4 fluxes from wetlands, permafrost thaw, and wildfires would further increase concentrations of these gases in the atmosphere. (IPCC: ‘high confidence.’)

Possible Climate Futures, part 5: GHG Emissions Have Caused Changes in Climate Irreversible For Centuries to Millenia

– Past GHG emissions since 1750 have committed the global ocean to future warming; (IPCC: ‘high confidence,’)
– Upper ocean stratification and ocean acidification will continue in to the 21st century with virtual certainty, and ocean deoxygenation will increase with high confidence;
– Changes are irreversible on centennial to millennial time scales in global ocean temperature; (IPCC: ‘very high confidence,’)
– Mountain and polar glaciers will continue to melt for decades or centuries; (IPCC ‘very high confidence,’)
– Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and likely for the Antarctic Ice Sheet;
– It is virtually certain that the global mean sea level will increase over the remainder of the century. Under the very low GHG emissions scenario, sea level rise by 2100 will be 0.28-0.55m; under the very high GHG emissions scenario we may see a rise of 0.63-1.01m;
– Over the next 2,000 years, the global mean sea level will rise by about 2-3m if warming is limited to 1.5C or 19-22m with 5C of warming, continuing to rise for millennia. (IPCC: ‘low confidence.’)

TLDR: What does this all mean?

Unfortunately, the situation may be as dire as reported. The impacts of anthropogenic climate change on our planet are irreparable in many instances, with the coldest, hottest, wettest, and driest places all but guaranteed to be hit the hardest. Sea levels will continue to rise, and the waters will continue to warm. Global warming is far from the cheeriest of topics, but it is inescapable and requires immediate attention. Individual action and proactivity is wonderful, but will not make a difference in the long run.

Are there any positives?

Potentially. Of the variety of scenarios predicted, it is unlikely states will abide by SSP1-1.9, but we may be able to hope for SSP1-2.6 – and here, the IPCC’s predictions offer a less favorable but more than likely manageable outcome. Also, the International Criminal Court is now deeming ‘ecocide‘ as a triable crime, hopefully kick starting a legal wave and shift in attitudes towards man-made irreversible acts committed by those pretending climate destruction is not of their concern.

In part four, Limiting Future Climate Change, the IPCC discusses what we need to do to reduce the effects of global warming. It is not as detailed as the remainder of the publication, because the required acts to reduce GHGs are widely known, and have been for a long period. Regardless, both part three and four will be covered in the next blog post. If you would like further information about the overview above, the IPCC has also provided a 42-page Summary for Policy Makers, which can be found here.