Today an important new United Nations scientific report on climate change was published. It begins by concluding that there’s no doubt that human influence has warmed the atmosphere, ocean and land. Nobody is surprised, but it clears the air (pun intended) to have it stated in black and white by the U.N.
The report, specifically the Working Group I contribution to the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC), highlights a number of other interesting, and unfortunately mostly alarming issues, too. Below are the ones I found most intriguing and bear in mind that Working Group I focused on the physical science basis.
The current state
“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.”
“Human-induced climate change is already affecting many weather and climate extremes in every region across the globe.”
Possible climate futures
“Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.”
“Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.”
“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.”
Five scenarios of future annual emissions of CO₂. In the most optimistic scenario (SSP1-1.9) we’re able to coordinate our efforts globally so that carbon neutrality is achieved around 2055. Source: IPCC AR6 WGI Summary for Policymakers.
Risk assessment and regional adaptation
“With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Changes in several climatic impact-drivers would be more widespread at 2°C compared to 1.5°C global warming and even more widespread and/or pronounced for higher warming levels.”
Limiting future climate change
“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.”
“Strong, rapid and sustained reductions in CH4 [Methane] emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.”
Scenarios with low or very low greenhouse gas (GHG) emissions (SSP1-1.9 and SSP1-2.6) lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios (SSP3-7.0 or SSP5-8.5)
Conclusion
This report is important for many reasons but the New York Times pointed out two key points. First, the report, which is approved by 195 governments and based on more than 14,000 studies, represents the most comprehensive summary to date of the physical science of climate change. Second, the report will be in the center when diplomats gather in November at a U.N. summit in Glasgow (COP26) to discuss how to step up their efforts to reduce emissions.
Despite all the doom and gloom, there are some optimistic tones in the report as well. If humanity can orchestrate a coordinated global effort to stop spewing CO2 to the atmosphere by 2055 (as illustrated by the optimistic scenario SSP1-1.9), global warming would likely halt and level off at around 1.5°C. That would require moving away from fossil fuels starting immediately, as well as removing large amounts of carbon from the atmosphere.
The AR6 is, however, still missing contributions from the two other groups, i.e. Working Group II (Impacts, Adaptation and Vulnerability) and Working Group III (Mitigation of climate change). Originally all three deliverables were scheduled to be approved and published before COP26, but sadly, reports II and III (and the Synthesis Report) have been postponed to 2022.
Needless to say it would’ve been extremely beneficial if policymakers would have had access to the entire AR6 before COP26 – but it’s good that at least this essential part was now published.
You can also expect that leaks of draft versions (like the one we had in June) will continue to surface during the next few months.