The Intergovernmental Panel on Climate Change (IPCC) released a dire report Monday warning that the world was already locked into more weather-related disasters, higher sea levels and more acidic oceans, and other significant changes to the planet due to greenhouse gases humans have sent into the atmosphere since the 1850s. United Nations Secretary General António Guterres called the report's findings "a code red for humanity" and said we owe it to "the entire human family" to cut emissions fast and sharply to avoid irreversible catastrophe.
But amid the stark warnings of "unprecedented" environmental changes human actions are provoking, the IPCC said the worst-case scenario it laid out in its 2013 report is actually less likely eight years later.
The 234 climate scientists who compiled IPCC's sixth report laid out five scenarios, based on how much action countries take to combat climate change. In each scenario, the world fails to meet the most ambitious target from the 2015 Paris climate agreement: keeping the rise in global temperatures under 1.5 degrees Celsius above preindustrial levels. The world is now expected to surpass that mark in the 2030s.
Under the best-case scenario — humanity replaces fossil fuels with renewable energy by 2050 and changes how it eats, lives, and travels — the temperature would drop slightly after hitting 1.5 degrees next decade. In the worst case, in which the world takes no action, global temperatures would be about 3.3 degrees Celsius above 19th century levels by the end of the century. The past five IPCC reports assumed the world was on this hottest "business as usual" path, but now the climate scientists see us somewhere in between either slowing emissions considerably or reducing them slightly, according to study co-author Claudia Tebaldi, a scientist at the U.S. Pacific Northwest National Lab.
"We are a lot less likely to get lucky and end up with less warming than we thought," said Zeke Hausfather at the Breakthrough Institute and a report co-author. "At the same time, the odds of ending up in a much worse place than we expected if we do reduce our emissions are notably lower."
"Things are going to change for the worse. But they can change less for the worse than they would have, if we are able to limit our footprint now," Tebaldi said. "Every little bit counts."