Just the Facts: The Climate Change Report One Month Later

It has been a month since the Intergovernmental Panel on Climate Change (IPCC) released its latest Assessment (Assessment Report 6). The publication was consequential: it was both a rigorous detailing of climate change impacts and filled with incredibly bad news for our future.

For me, the media reporting on the IPCC Assessment suffered in three respects. Many of the stories cherry-picked from the results and did not provide a sense of the broad scope of the report. Some reporters suggested that the IPCC Assessment was hard to understand due to technical language, which had the effect of discouraging readership. Perhaps most importantly, since the report came out, the news cycle has moved on to other stories — the Covid resurgence and Afghanistan — which are important news now, but which long term will not have anything close to the effect on the earth and its people that the new information on climate change details.

I thought, therefore, it might be helpful one month later to provide a simple list of quotes from the IPCC Assessment summary to show that the report is indeed accessible as well as to make clear the breadth and impact of what it says. The list seeks to avoid picking and choosing from the report, and does not include editorial from me. I have only included some definitions of terms where I thought it might be helpful.

Here goes:

It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.

[Note: “cryosphere” = those parts of the earth, land or sea, that are covered with frozen water.]

Each of the last four decades has been successively warmer than any decade that preceded it since 1850

Global surface temperature was 1.09 [0.95 to 1.20] °C higher in 2011– 2020 than 1850–1900, with larger increases over land (1.59 [1.34 to 1.83] °C) than over the ocean (0.88 [0.68 to 1.01] °C)

[Note: 1.09 degrees Centigrade = 1.96 degrees Fahrenheit]

It is very likely that well-mixed GHGs were the main driver of tropospheric warming since 1979

[Note: “GHG”=Greenhouse Gases, primarily carbon dioxide and methane. “Troposphere” = lowest region of the atmosphere, from ground level up 4–6 miles]

Human influence is very likely the main driver of the global retreat of glaciers since the 1990s and the decrease in Arctic sea ice area between 1979–1988 and 2010–2019 (about 40% in September and about 10% in March)

It is virtually certain that human-caused CO2 emissions are the main driver of current global acidification of the surface open ocean

Global mean sea level increased by 0.20 [0.15 to 0.25] m between 1901 and 2018

The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years

In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years (high confidence)

[Note: “confidence” indicated in the report is an assessment of confidence in the statement by the panel — 90% for “very high confidence,” 80% for “high,” and 50% for “medium.” I’ve included few medium confidence quotes in this list and no low confidence quotes.]

Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years (high confidence)

Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years (high confidence)

Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5

[Note: “AR5” = the IPCC Assessment Report 5, 2014]

It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with high confidence that human-induced climate change is the main driver of these changes. Some recent hot extremes observed over the past decade would have been extremely unlikely to occur without human influence on the climate system

The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence)

Event attribution studies and physical understanding indicate that human-induced climate change increases heavy precipitation associated with tropical cyclones (high confidence)

Human influence has likely increased the chance of compound extreme events since the 1950s. This includes increases in the frequency of concurrent heatwaves and droughts on the global scale (high confidence); fire weather in some regions of all inhabited continents (medium confidence); and compound flooding in some locations (medium confidence)

The rate of ice sheet loss increased by a factor of four between 1992–1999 and 2010–2019. Together, ice sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006–2018. (high confidence)

Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered

Compared to 1850–1900, global surface temperature averaged over 2081–2100 is very likely to be higher by 1.0°C to 1.8°C under the very low GHG emissions scenario considered (SSP1–1.9), by 2.1°C to 3.5°C in the intermediate scenario (SSP2–4.5) and by 3.3°C to 5.7°C under the very high GHG emissions scenario (SSP5–8.5)

[Note: “SSP” refers to scenarios for socio-economic development with lower SSP scenarios implying a shared approach to solving energy/climate issues, with broader progress addressing climate change, and higher SSP scenarios referring to more divisive approaches among countries and socio-economic groups, with less progress.]

The last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago (medium confidence)

every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes, including heatwaves (very likely), and heavy precipitation (high confidence), as well as agricultural and ecological droughts in some regions (high confidence)

There will be an increasing occurrence of some extreme events unprecedented in the observational record with additional global warming, even at 1.5°C of global warming

A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought (high confidence)

Monsoon precipitation is projected to increase in the mid to long term at global scale, particularly over South and Southeast Asia, East Asia and West Africa apart from the far west Sahel (high confidence)

Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level

It is virtually certain that global mean sea level will continue to rise over the 21st century. Relative to 1995–2014, the likely global mean sea level rise by 2100 is 0.28–0.55 m under the very low GHG emissions scenario (SSP1–1.9), 0.32–0.62 m under the low GHG emissions scenario (SSP1–2.6), 0.44–0.76 m under the intermediate GHG emissions scenario (SSP2–4.5), and 0.63–1.01 m under the very high GHG emissions scenario (SSP5–8.5)

In the longer term, 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)

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

At 2°C global warming and above, the level of confidence in and the magnitude of the change in droughts and heavy and mean precipitation increase compared to those at 1.5°C. Heavy precipitation and associated flooding events are projected to become more intense and frequent in the Pacific Islands and across many regions of North America and Europe (medium to high confidence)

It is very likely to virtually certain that regional mean relative sea level rise will continue throughout the 21st century, except in a few regions with substantial geologic land uplift rates

Due to relative sea level rise, extreme sea level events that occurred once per century in the recent past are projected to occur at least annually at more than half of all tide gauge locations by 2100 (high confidence)

Relative sea level rise contributes to increases in the frequency and severity of coastal flooding in low-lying areas and to coastal erosion along most sandy coasts (high confidence)

Cities intensify human-induced warming locally, and further urbanization together with more frequent hot extremes will increase the severity of heatwaves (very high confidence)

In coastal cities, the combination of more frequent extreme sea level events (due to sea level rise and storm surge) and extreme rainfall/riverflow events will make flooding more probable (high confidence)

Many regions are projected to experience an increase in the probability of compound events with higher global warming (high confidence). In particular, concurrent heatwaves and droughts are likely to become more frequent

Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming cannot be ruled out and are part of risk assessment

Abrupt responses and tipping points of the climate system, such as strongly increased Antarctic ice sheet melt and forest dieback, cannot be ruled out (high confidence)

The Atlantic Meridional Overturning Circulation is very likely to weaken over the 21st century for all emission scenarios

[Note: “Atlantic Meridional Overturning Circulation” = the Gulf Stream]

From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions

This Report reaffirms with high confidence the AR5 finding that there is a near-linear relationship between cumulative anthropogenic CO2 emissions and the global warming they cause. Each 1000 GtCO2 of cumulative CO2 emissions is assessed to likely cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C4

[Note: “Anthropogenic” = originating from human activity. “GtCO2” = gigatonnes of carbon dioxide. A gigatonne is 2.2 trillion pounds.]

Anthropogenic CO2 removal (CDR) has the potential to remove CO2 from the atmosphere and durably store it in reservoirs (high confidence)

[Note: “CDR” = carbon dioxide removal]

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