Climate Action Is Slow—But It Will Still Curb Extreme Heat
Ten years after the Paris climate agreement, the limited progress we’ve made in reducing global warming means that there will be less extreme heat in the future than there would be without the accord. In the decade since the Paris climate agreement was hammered out, countries have made only halting efforts toward meeting the accord’s goal of limiting global warming. But even that modest progress means that the world will have to deal with far less extreme heat in the future than it otherwise would.
This is a clear example, climate experts say, of why it is important to push forward with even imperfect progress. That is one of the messages scientists, environmental groups, and some of the nations that are most affected by the effects of climate change—including extreme heat—are stressing at COP30, this year’s annual United Nations Climate Change Conference on implementing the Paris Agreement, which is happening now in Brazil.
Research shows that global warming is making heat waves more frequent, longer-lasting, and more intense everywhere. They are already the deadliest weather-related killer, and that trend is accelerating. Deaths in the U.S. related to extreme heat have jumped by 53 percent over the last decade compared with a 7 percent increase in deaths related to cold, according to a recent study in JAMA Network Open. And globally, heat-related deaths have risen by 63 percent since the 1990s, according to “The 2025 Report of the Lancet Countdown on Health and Climate Change.”
When the Paris Agreement was drafted in 2015, global temperatures had risen by about one degree Celsius above what are called preindustrial levels—where such temperatures were in the late 19th century, before the heat-trapping effect of widespread fossil fuel burning became detectable in the record. In the landmark Paris accord, 194 countries agreed to keep any further temperature rise to “well below” two degrees C and to make all attempts to keep it under 1.5 degrees C.
Though 2024 was the first year with a global average temperature above 1.5 degrees C, the long-term warming signal that the Paris Agreement is pegged to—an average of many years—is currently at around 1.3 degrees C above preindustrial levels. Three tenths of a degree above 2015 levels sounds small, but it’s enough that, globally, people are experiencing an average of 11 more of the most extremely hot days every year, according to a recent joint study by the research nonprofits Climate Central and World Weather Attribution. (They defined those days as the hottest 10 percent of days in any particular country.) For some countries, the increase has been higher.
But even the limited progress under the Paris Agreement is having a discernible impact. Before the agreement, the world was on track for four degrees C of warming, which would have caused an average of 114 more of the hottest days each year. (For some countries, such as Indonesia, that number could skyrocket to more than 300 extra days.) We’re now on track for between 2.5 to three degrees C of warming, which would slash the number of extra extremely days in half. “Every fraction of a degree of warming—whether it is 1.4, 1.5, or 1.7°C—will mean the difference between safety and suffering for millions of people,” said Friederike Otto, a climate scientist at Imperial College London and a co-author of the recent joint study, in a press release.
The study also looked at some recent heat waves that likely killed tens of thousands and drove drought and wildfires, which further underscores the difference that limiting warming to even 2.6 degrees C can make. With four degrees C of overall warming, such heat waves would be anywhere from three to six degrees C hotter than today and five to 75 times as likely to occur. With 2.6 degrees C of warming, they would be 1.5 to three degrees C hotter and three to 35 times more likely.
Whether countries will follow through with their obligations is by no means certain, as was made clear by President Donald Trump’s decision to withdraw the U.S. from the pact on his first day in office and his efforts to ramp up U.S. fossil fuel production. But there are some positive signs, such as the fact that emissions from China—currently the largest national source—have either been flat or falling over the past 18 months. Solar and wind energy generation has also more than tripled since 2015, and investment in clean energy has outstripped that in fossil fuels. And local and state officials from the U.S. are attending the meeting to signal that they still want to act to curtail the country’s emissions.
The key question from the COP30 meeting will be whether the countries that are still participating make further, concrete commitments to reduce emissions beyond those that were already promised.
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