U.S. Paris Exit Raises Global Climate Forecast

The United States added 133 megatons of carbon dioxide equivalent in 2025, more than any other country, and accounted for 70% of the emissions increase among countries whose emissions rose, a United Nations report said. Higher electricity demand and a rebound in coal power generation drove the rise. The report also tied its worse global warming outlook partly to the U.S. formally withdrawing from the Paris Agreement.

The U.S. and the global emissions picture

Of the 124 countries that increased emissions in 2025, their combined total rose by 189 million tons of carbon dioxide. Sixty-three countries, including most European nations, cut emissions. The report said the United States was the only major economy that neither reduced carbon pollution nor slowed the growth of fossil-fuel emissions. Every other top 20 major economy reduced pollution or slowed its growth.

The United Nations Environment Programme’s updated calculations estimate that Earth will warm another 1.2 degrees Celsius above current temperatures if countries meet their submitted climate plans. That projection is 0.1 degrees Celsius higher than the same science team’s estimate last year. The report linked the change to “the formal withdrawal of the United States of America from the Paris Agreement and revised estimates of historical emissions.”

Climate plans still leave the globe 2.6 degrees Celsius hotter than pre-industrial times by 2100. Without national promises, the current path would bring warming to 2.8 degrees Celsius above temperatures in the second half of the 19th century, unchanged from last year’s projection. Both estimates exceed the Paris climate pact’s goal of limiting warming to below 2 degrees Celsius, preferably 1.5 degrees.

Warnings and projected costs

The world is now about 1.4 degrees Celsius warmer than pre-industrial times. United Nations officials concede that limiting warming to 1.5 degrees is no longer possible. Instead, they hope to hold warming to about 1.8 degrees Celsius before removing enough carbon dioxide from the air to bring temperatures back down to 1.5 degrees.

United Nations Secretary-General António Guterres said the world is falling “dangerously short” of its goals, “but we have the tools to change course and pull back from the brink.” UNEP Executive Director Inger Andersen said cutting global carbon emissions by 18% by 2030 and 69% by 2040 “is the only way that we can get back to a semblance of a reality that is still largely manageable without major impacts and therefore that makes every sense.”

Report lead author Anne Olhoff, director of UNEP Copenhagen Climate Centre, said the U.S. policy change would most likely add one-tenth of a degree Celsius to global temperatures by the end of the century. Climate scientist Adelle Thomas, who did not take part in the study, said: “The report's message is clear. We know what needs to be done. We have the tools to do it. And delay only makes the challenge more dangerous and more expensive for all.”

Responses to the U.S. policy change

Australian climate scientist Bill Hare, CEO of Climate Analytics, said the United States is going “hell-for-leather trying to block renewables while actively promoting and subsidizing dirty coal.” He added that U.S. diplomacy is trying to persuade other countries to pull back on action. Hare did not take part in the U.N. report, but said, along with several other outside scientists, that it was scientifically sound.

Mohamed Adow, director of Power Shift Africa, said the U.S. retreat “has real consequences for the planet and for millions of people around the world.” He pointed to the risks of heat waves, floods, failed harvests and deaths, particularly for vulnerable communities in Africa. Hare said the extra tenth of a degree could put another 140 million people “into dangerously hot conditions” and raise the odds of collapse of the Amazon rainforest or ice sheets in Greenland and Antarctica. University of Pennsylvania climate scientist Michael Mann said it would shave about $1.2 trillion from the global economy.

Johan Rockstrom, director of the Potsdam Institute for Climate Impacts Research in Germany, said the U.S. effect could be larger than the U.N. calculation if other nations ease their efforts. Australian climate scientist Malte Meinshausen said the rest of the world is “exhausted” by damage the U.S. is willingly doing to allies, multilateral structures, economic cooperation and disaster relief. The report and quoted responses focus on emissions, climate targets and projected impacts; they don't provide figures on domestic demographic effects or identify popular opposition to the policy change.