Today we'll start our reading of the new IPCC climate report.
In this post you'll find a summary of the "Summary for Policymakers," along with questions, observations, and some resources. We're following the online reading plan laid out here.
1: SUMMING UP
The Summary begins by asserting a finding: that human activities have warmed the world. The document breaks this down by parts of the world (sea, land, different atmospheric layers) and by degrees of certainty, along with room for some unevenness of cause and effect. Consequences include increased rain overall, decreased ice and snow mass, shifting some storm tracks towards the north and south poles, sea level rise, extension of growing seasons in northern hemispheric temperate regions, "climate zones have shifted poleward in both hemispheres," and ocean acidification. How much have we heated the world? "The likely range of total human-caused global surface temperature increase from 1850–1900 to 2010–201911 is 0.8°C to 1.3°C, with a best estimate of 1.07°C."
The main human-created sources of climate change start with carbon dioxide, followed by methane. Several sources actually reduce temperatures:
This human intervention into the climate represents a clear break from thousands of years of history:
The Summary goes on to describe extreme hot weather events rising, including heat waves, great rainfall in monsoons, more rain in general, droughts, and tropical cyclones. Compound hot weather events are also more likely - i.e., when two or more occur at the same time and overlap. At the same time, extreme cold weather events are gradually decreasing. The report finds humanity playing some role in making this transformation occur.
Where excessive rain and more droughts are most likely to occur, seen through a schematic map.
Oceans play by far the largest role in soaking up increased temperatures: "Ocean warming accounted for 91% of the heating in the climate system, with land warming, ice loss and atmospheric warming accounting for about 5%, 3% and 1%, respectively..." However, if global temperature rise hits higher ranges, the atmosphere will pick up more of the heat.
The 2021 Summary finds that equilibrium climate sensitivity is around 3°C. ECS is an estimate of how much the world will ultimately warm, once the planet reaches a new equilibrium with incoming solar radiation.
Based on multiple lines of evidence, the very likely range of equilibrium climate sensitivity is between 2°C (high confidence) and 5°C (medium confidence). The AR6 assessed best estimate is 3°C with a likely range of 2.5°C to 4°C (high confidence)...
The Summary continues by offering five different scenarios for how much greenhouse gas output humanity might produce and how that can impact global temperatures over the rest of this century. Each is named for a different "Shared Socio-economic Pathway," or SSP:
The report offers several wild cards or unusual events which may have an outsized impact. One possibility is the chance of a major volcanic eruption, perhaps somewhat greater than those of Mount Pinatubo (1991) or Novarupta (1912). This form of nonhuman geoengineering might cool temperatures by ejected huge amounts of particles into the atmosphere, which then circulate globally:
C.1.4 Based on paleoclimate and historical evidence, it is likely that at least one large explosive volcanic eruption would occur during the 21st century. Such an eruption would reduce global surface temperature and precipitation, especially over land, for one to three years, alter the global monsoon circulation, modify extreme precipitation and change many CIDs (medium confidence). If such an eruption occurs, this would therefore temporarily and partially mask human-caused climate change.
In the opposite direction is the low-probability chance of a suddenly quickened ice sheet collapse. That's for the most extreme scenario, SSP5-8.5, and would "result... from ice sheet instability processes characterized by deep uncertainty and in some cases involving tipping points..." This could surge ocean levels beyond anything else discussed:
Beyond the year 2100, the changes described so far will last for centuries. Higher levels of ocean acidification, higher ocean temperatures, smaller icepacks, reduced permafrost, and sea level rise will persist for a long time. In particular, on oceans:
sea level is committed to rise for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and will remain elevated for thousands of years (high confidence). Over the next 2000 years, global mean sea level will rise by about 2 to 3 m if warming is limited to 1.5°C, 2 to 6 m if limited to 2°C and 19 to 22 m with 5°C of warming, and it will continue to rise over subsequent millennia (low confidence).
What is to be done? The IPCC summary is quite clear: a mix of zeroing out carbon emissions along with drawing down and storing already lofted CO2.
Achieving global net zero CO2 emissions is a requirement for stabilizing CO2-induced global surface temperature increase, with anthropogenic CO2 emissions balanced by anthropogenic removals of CO2.
Cutting down methane and other GHG is good, too.
2: QUESTIONS
Which scenario is most likely to occur, in your view?
How would zeroing out carbon emissions and cutting back emissions impact your life and your academic work?
How can we best communicate the Summary's findings to a broader audience?
Do the IPCC's projections look dangerous enough to justify the risks of geoengineering?
What should higher education do in the wake of this new report?
3: REFLECTIONS
Overall, the new IPCC report confirms much of what I already researched about anthropogenic climate change. That doesn't take away from its value, I think. Instead, continuities with other research show the science crystallizing. That said, the ECS is lower than it was in earlier reports. There is more confidence in findings.
The scenarios are bare bones, just consisting of changed metrics along a similar line of datapoints. But I think we can build on them.
I haven't seen many academic responses so far. By that I mean academics reflecting on what this means for higher education.
Writing all of the preceding took some self-control, as emotions of dread continued to hit me, even after being immersed in the subject for years.
4: MORE INFORMATION
From the IPCC, a press release. A Trello board. An interactive atlas.
Michael Mann, one of the world's leading climatologists, offers his reflections.
Introduction at The Conversation by Robert Kopp, Professor, Department of Earth & Planetary Sciences, and Director, Rutgers Institute of Earth, Ocean, and Atmospheric Sciences, Rutgers University.
The New York Times has a good introduction with some reactions.
...and now over to you. What do you think of the summary? Is there anything we should focus on? Want to try one of the questions?
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