Some of the extra energy trapped by these gases warms the atmosphere and the land, as well as melting the planet’s ice.
The world’s glaciers had one of their five worst years on record in 2024/25, according to provisional data, while sea ice at both poles was at or near record lows throughout most of 2025.
But more than 90% of the Earth’s extra energy heats the oceans, which in turn harms marine life, drives more intense storms and contributes to sea-level rise.
The heat stored in the upper 2km (1.2 miles) of the global ocean reached a new high last year, the WMO says. Over the past two decades, it has been warming more than twice as quickly as during the late 20th Century.
“Human activities are increasingly disrupting the natural equilibrium and we will live with these consequences for hundreds and thousands of years,” said Prof Celeste Saulo, secretary general of the WMO.
The report points to the impacts of rising temperatures today, which are helping to intensify many types of extreme weather and aiding the spread of diseases such as dengue.
The south-west US is currently in the midst of a record-breaking early-season heatwave, with temperatures exceeding 40C in places over recent days – about 10-15C above average.
Rapid analysis by scientists at the World Weather Attribution group on Friday found that intensity of heat would have been “virtually impossible” without human-caused climate change.
Researchers are also closely watching the Pacific Ocean, with long-term forecasts strongly suggesting that a warming El Niño phase could form in the second half of 2026.
An El Niño – on top of the background human-caused warming trend – could push temperatures to new heights into 2027.
“If we transition to El Niño we will see an increase in global temperature again, and potentially to new records” said Dr John Kennedy of the WMO.