The world is falling further behind in efforts to combat climate change and faces a hotter future than scientists projected last year, with the US contributing significantly to the worsening outlook, according to a new United Nations report.
Even if all countries fulfil their pledges to cut heat-trapping emissions, global temperatures are expected to rise another 1.2 degrees Celsius (2.2 degrees Fahrenheit) above current levels, according to updated climate projections released on Wednesday by the United Nations Environment Programme (UNEP).
The estimate is about 0.1 degrees Celsius (0.2 degrees Fahrenheit) higher than the projections made by the same scientific team last year.
"This is a worse outcome than expected last year, as a result of the formal withdrawal of the US from the Paris Agreement and revised estimates of historical emissions," the report said.
The report also pointed to increased US emissions last year, noting that all other major economies among the world's top 20 either reduced their carbon pollution or slowed the growth in carbon dioxide emissions from burning coal, oil and gas.
The increase in US emissions, at 133 million tonnes of carbon dioxide equivalent, far exceeded that of any other country and was driven by rising electricity demand and a rebound in coal-fired power generation, the report said.
Of the 189 million tonnes of additional carbon dioxide emissions recorded in 2025 by 124 countries whose emissions increased, excluding the 63 countries that recorded declines, around 70% came from the US, according to the report.
The US is going "hell-for-leather trying to block renewables while actively promoting and subsidising dirty coal — and its diplomacy is trying to make other countries also pull back on action," said Australian climate scientist Bill Hare, chief executive of Climate Analytics, which assesses countries' climate action plans.
"It is looking at the fire, denying there is a fire, and then pouring more petrol on it," he said.
Hare was not involved in the UN report but, like several other independent scientists, said its findings were scientifically sound.
Global warming projected to exceed Paris climate targets
The updated projections show that global temperatures could rise by 2.6 degrees Celsius (4.7 degrees Fahrenheit) above pre-industrial levels by 2100 if countries fulfil the climate action plans they have submitted to the United Nations.
If the world continues along its current path without those national commitments, temperatures are projected to rise by 2.8 degrees Celsius (5 degrees Fahrenheit) above levels recorded in the second half of the 19th century, unchanged from last year's estimate.
Both scenarios would significantly exceed the targets set under the 2015 Paris climate agreement, which aims to limit global warming to well below 2 degrees Celsius (3.6 degrees Fahrenheit) and preferably 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels.
Global temperatures have already risen by around 1.4 degrees Celsius (2.5 degrees Fahrenheit) above pre-industrial levels.
Earlier this year, and again in the latest report, UN officials acknowledged that limiting warming to the 1.5-degree target is no longer achievable. Instead, they are hoping to restrict warming to around 1.8 degrees Celsius (3.2 degrees Fahrenheit) before removing enough carbon dioxide from the atmosphere to bring temperatures back down to 1.5 degrees.
The world is falling "dangerously short" of even those targets, UN Secretary-General António Guterres said, adding that the tools needed to change course and avoid the worst consequences remain available.
Cutting global carbon emissions by 18% by 2030 and 69% by 2040 is essential to bringing the climate situation back to a more manageable level, said UNEP Executive Director Inger Andersen.
"The report's message is clear," said climate scientist Adelle Thomas, vice-chair of a UN scientific assessment on climate impacts who was not involved in the study.
"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," she said.
Additional warming poses serious risks
Anne Olhoff, the report's lead author and director of the UNEP Copenhagen Climate Centre, said the shift in US policy would likely add 0.1 degrees Celsius (nearly 0.2 degrees Fahrenheit) to global temperatures by the end of the century.
"This report shows that America's retreat isn't just a political embarrassment. It has real consequences for the planet and for millions of people around the world," said Mohamed Adow, director of the climate organisation Power Shift Africa.
"An extra tenth of a degree might sound insignificant, but in climate terms it is enormous. It means more dangerous heatwaves, more destructive floods, more failed harvests and more lives lost," he said, adding that every fraction of a degree matters for vulnerable African communities already on the front lines of the climate crisis.
Hare said the additional 0.1 degrees Celsius of warming could expose another 140 million people to dangerously high temperatures and increase the risk of the collapse of the Amazon rainforest and ice sheets in Greenland and Antarctica.
The added warming could also cost the global economy around $1.2 trillion, said Michael Mann, a climate scientist at the University of Pennsylvania.
Johan Rockström, director of Germany's Potsdam Institute for Climate Impacts Research, said the impact of US policy could be even greater than the UN estimates because other countries might scale back their climate efforts if the world's largest historical emitter does less to combat global warming.
"The rest of the world is exhausted when it comes to counting the damage that the US is willingly doing to allies, multilateral structures, economic cooperation, disaster relief," Australian climate scientist Malte Meinshausen said.
"The rest of the world should probably continue to focus even less on the US," he added.