Wildfires, heat-related deaths, loss of jobs, and wrecked coastal infrastructure: These are just a few of the damages that overshooting temperatures “well below 2°C” would cause, according to a report written by 270 scientists convened by the United Nations Environment Programme and the World Meteorological Organization.
“This assessment for the first time analyzes and assesses in very high detail the impact of a temporary overshoot. And the report clearly indicates that there will be some impacts that will be irreversible even if the temperature will return to 1.5°C at the end of the century. That is one of the major, major findings of this report,” said Hoesung Lee, chair of the Intergovernmental Panel on Climate Change (IPCC), which released the report today.
Overshoot is an option discussed by scientists and policymakers to achieve a global average temperature “well below 2°C” by the end of the century. The option includes letting global temperatures rise above 1.5°C or higher and then using carbon capture to bring temperature back down in a few decades. Carbon capture relies on reforesting and restoring coastal and marine ecosystems as well as developing massive direct air capture and bioenergy carbon capture and storage technology.
Although limiting temperature in the long run brings more benefits than global temperatures rising 3°C, 4°C, or 5°C permanently, overshooting has severe downsides, according to the latest report. Glaciers that supply water to millions of people, coral reefs that are among the most biodiverse ecosystems on Earth, and storm-abating wetlands will be lost and won’t be recovered after temperatures rebound.
Recent work suggests financial advantages to avoiding overshoot: Global gross domestic product (GDP) will be up to 2% larger by the end of the century with no overshoot, according to a paper in Nature Climate Change last year. GDP would grow faster in the second half of the century because carbon prices would relax and less money would go toward mitigating climate change, leading to “far larger” long-term growth than the short-term GDP dampening required to avoid overshoot.
“Overshoot isn’t a solution—it’s a mistake,” said NASA climate scientist Kate Marvel, who was not involved in the report.
No Substitute for Reducing Emissions
“There are smart ways of doing carbon dioxide removal, and the technology is rapidly advancing. We absolutely need to remove carbon dioxide from the atmosphere to meet our targets,” Marvel said. “But we also need to cut emissions as quickly as possible. There is no substitute for this, and we can’t rely on our future civilization adopting large-scale negative emissions to clean up our mess.”
Overshooting would erase “ecosystems that are absolutely critical to underpinning the livelihoods of often the most vulnerable [people] in the world,” said Debra Roberts, a cochair of IPCC Working Group II, which wrote the latest report.
To avoid overshoot, humans need to reduce emissions by 45% by 2030 and achieve net zero emissions by 2050. Current global commitments show emissions rising almost 14% this decade, according to U.N. Secretary-General António Guterres.
Although avoiding overshoots is more expensive in the short term because it involves stronger cuts to fossil fuels, it “will leave us better off in the long-run as we avoid costly net-negative emissions in the future,” wrote climate stabilization researcher Daniel Johansson at Chalmers University of Technology in Sweden last year in Nature Climate Change.
The risk of heat waves becoming more frequent and longer “increases much more rapidly with temperature overshoot than without,” said Laurent Drouet, who did not participate in the IPCC report. Drouet is the author of a recent study on the risks of overshoot published in Nature Climate Change.
Overshoot could also kick off harmful feedback loops that would release more greenhouse gases. Natural ecosystems like permafrost store vast amounts of carbon in the ground; warming temperatures could start a self-propelling thaw cycle that would be likely impossible to stop.
Required: Bold and Rapid Action
The IPCC report notes that overshoot consequences are less severe with shorter durations of overshoot and lower temperature levels of overshoot.
What can be done to avoid overshoot? Ending coal use and investing in renewable energy are two immediate solutions. Lack of societal and political will is one of the largest roadblocks to change, according to the report.
“It’s important that we ourselves educate ourselves about the challenges we face,” said Roberts, “and make those priorities known more broadly in society and to our leadership in order to encourage the political will that’s necessary to take the bold and rapid action required in this decade.”
—Jenessa Duncombe (@jrdscience), Staff Writer