Countries gathered at the COP31 climate summit in Turkey are still talking about a goal that is increasingly out of reach: limiting warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, NPR reported.
Globally, average temperatures are already close to 1.5 degrees Celsius warmer than they were before the Industrial Revolution. Heat-trapping emissions from burning fossil fuels are still rising, and most countries are not on track to meet their pledges to cut emissions. The best-case scenario for the planet is now 1.7 or 1.8 degrees Celsius of warming, according to a recent United Nations study. If fossil fuel emissions stay on their current path, the world would be around 2.8 degrees Celsius, or 5 degrees Fahrenheit, hotter by the end of the century.
The difference between 1.5 and 2 degrees may sound tiny. Research shows those increments can produce sharply different outcomes. "The crucial point is that every fraction of a degree matters," said Tim Lenton, a climate professor at the University of Exeter. "Every fraction of a degree that we avoid is really able to do a huge amount of limiting harm."
Coral reefs already close to the edge
Corals build the framework that supports vast numbers of other species, and they are vital to hundreds of millions of people who depend on reefs for food and livelihoods. They are also highly vulnerable to heat. Prolonged marine heat waves cause corals to bleach, which can eventually kill them. Since the late 1990s, there have been four global bleaching events. With a historically strong El Niño now raising water temperatures, scientists say a fifth global bleaching event is likely unfolding, NPR reported.
Even before the previous bleaching event from 2023 to 2025, researchers found that 44 percent of coral species globally are at risk of extinction. "These are incredibly worrying statistics, but they also emphasize that time matters," said David Obura, director of the coral research organization CORDIO East Africa, who worked on the study published last month in the journal Nature. "Every ten years, every five years counts."
The Intergovernmental Panel on Climate Change found that beyond 2 degrees Celsius of warming, 99 percent of corals would be lost. "At 2 degrees of warming, we anticipate most corals just won't survive, not in functional ways to build a reef ecosystem," Obura said. Conservation groups and coastal communities are still working to make reefs healthier so they can better withstand warming, including by restoring corals, reducing water pollution and breeding more heat-tolerant corals.
Heat, storms and 140 million people per tenth of a degree
Researchers have found that for every tenth of a degree of warming, an additional 140 million people are exposed to dangerous levels of heat. Heat waves are already causing heavy death tolls, including in Europe, where an estimated 50,000 people died of heat-related causes this past summer, NPR reported. Heat is particularly dangerous for people with chronic health conditions, as well as for those who are elderly or pregnant, and many heat-related deaths are undercounted.
Every degree of warming also affects storms. Warmer air can produce heavier downpours because it holds 7 percent more water vapor for every degree, and rainstorms are already getting more intense in most of the United States. The 1.5-degree target is no longer the most likely outcome, but the negotiations in Turkey are still about how much worse the next increments will be — for reefs, for heat deaths, and for the storms that follow a warmer atmosphere.