The United Nations has acknowledged that Earth has lost its opportunity to prevent some of the most severe consequences of global warming, shifting its strategy to focus on limiting excessive temperature increases and then working to bring global temperatures back down. The new approach comes as the world is poised to exceed the 1.5 degrees Celsius (2.7 degrees Fahrenheit) threshold agreed upon in the 2015 Paris climate accord due to emissions from the burning of fossil fuels.
Earth is currently at approximately 1.4 degrees Celsius (2.5 degrees Fahrenheit) above pre-industrial levels, according to calculations by scientists. The UN report indicates that global temperatures are expected to cross the 1.5-degree threshold within the next few years. The most optimistic scenario projects warming peaking at 1.8 degrees Celsius (3.2 degrees Fahrenheit) around mid-century if countries pursue ambitious climate goals. However, current government policies are on track to push temperatures to 2.6 degrees Celsius (4.7 degrees Fahrenheit) above pre-industrial levels by 2100.
This developing situation means decades of increased weather-related disasters, rising sea levels, species extinctions, and melting ice and glaciers are likely unavoidable. "Humanity is speeding past the limit to avoid climate catastrophe," said United Nations Secretary-General António Guterres. The new strategy involves ending fossil fuel use and developing methods to remove carbon dioxide from the atmosphere.
"It's a reality check. We have to live with this warmer world," said Richard Betts, a climate scientist at the University of Exeter and a co-author of the report. "But there's still a lot we can do to limit warming."
The "Overshoot" Strategy
The report envisions a scenario where global temperatures pass the 1.5-degree limit, then peak, and gradually cool back below the threshold, ideally by the end of the century. This concept, termed "overshoot," requires a different approach from the previous focus on prevention. "Let’s be very clear, 1.5 target is still the goal. But now we need to approach it differently from above," said UNEP Executive Director Inger Andersen.
Scientists emphasize that every fraction of a degree of warming avoided still reduces damage. "Every tenth of a degree we avoid still means less damage," noted Andrew Weaver, a climate scientist at the University of Victoria who was not part of the study. The priority now is to limit the peak temperature reached and minimize the duration spent above the 1.5-degree mark. However, the world will likely remain in this "overshoot" period for "many, many decades," according to Betts.
Delays in reducing emissions significantly impact peak warming. "If we act now we can limit overshoot," the report states. "Not a safe world, but safer than remaining above" 1.5 degrees for the long term.
Unavoidable Impacts and Adaptation
Governments are urged to increase efforts to adapt to worsening climate impacts, which disproportionately affect vulnerable populations, as "some impacts simply cannot be avoided." The report labels this phase "coping and containment."
During the overshoot period, increased mortality and illness due to climate change and extreme weather events are expected. Food production may decrease, leading to hunger, water shortages are projected to worsen, economies could be damaged, and species like coral are at risk of extinction. The report also warns of potential "tipping points" with irreversible consequences, such as the loss of the West Antarctic and Greenland ice sheets, the Amazon rainforest's collapse, and the shutdown of the Atlantic Ocean circulation system.
Some locations may become uninsurable or even uninhabitable. The final phase of the overshoot strategy involves cooling the planet by removing carbon dioxide from the air. While planting trees is a traditional method, the report suggests it could only reduce global temperatures by about a tenth of a degree, necessitating more novel carbon removal approaches.
Some experts express skepticism about the feasibility of these newer methods, calling them unreliable and expensive. "We were unable to stop the runaway train of global emissions to avoid 1.5 C of warming," said Stanford University climate scientist Rob Jackson, who was not involved in the report. "Now overshoot scenarios require us to stop the train quickly and to back it up. Is it our best hope? Absolutely. Is it likely? Absolutely not."