Greenhouse gas concentrations, global sea level, and ocean heat all reached record highs in 2025, according to a comprehensive annual report published by the American Meteorological Society (AMS).
The international review, compiled with data from 625 scientists in 60 countries using monitoring stations and instruments on land, water, ice, and in space, paints a grim picture of Earth's climate.
The report found that harmful greenhouse gases, including methane and carbon dioxide, reached unprecedented levels, with fossil fuel emissions also hitting a new peak. Despite the absence of an El Niño event, which typically drives global temperatures higher, the planet experienced exceptional warmth. The data suggests that a potential 'Super El Niño' event could lead to even more extreme conditions in the coming years.
Key Climate Indicators in 2025
Analysis of climate data revealed that 2025 was among the three warmest years on record, which spans 175 years. The period from 2015 to 2025 represents the 11 warmest years recorded. Extreme warmth was observed globally, with Antarctica experiencing its warmest year on record since 1979 and the Arctic its second warmest since 1900. Europe recorded its hottest year ever, while Russia, China, South Korea, and Argentina each had their second warmest year.
Atmospheric carbon dioxide concentrations averaged 425.6 parts per million in 2025, a 53 percent increase compared to pre-industrial levels. Methane and nitrous oxide, other significant greenhouse gases, also reached record concentrations. Estimated fossil fuel emissions reached a record 10.3 petagrams of carbon, more than triple the levels recorded in the 1960s. These gases trap heat, contributing to planetary warming.
Warming Oceans and Rising Seas
The majority of excess heat generated is absorbed by the oceans, which have absorbed nearly 90 percent of the additional energy trapped within the Earth's system. Global ocean heat content, measured from the surface to 2,000 meters, reached a new high for the ninth consecutive year. Around 87 percent of the world's ocean surface experienced at least one marine heatwave in 2025, a significant increase compared to the 26 percent that experienced marine cold spells.
Sea surface temperatures were the third highest in the 172-year record, even under cool or weak La Niña-like conditions in the Pacific. Global sea levels have reached a record high for the 14th consecutive year, standing approximately 111 millimeters above the 1993 average. Warming oceans have contributed about 1.6 millimeters per year to sea-level rise since 2005, while melting glaciers and ice sheets have added an average of two millimeters per year.
Arctic Ice Loss and Glacial Melt
The Arctic is experiencing a dramatic loss of its oldest sea ice, with ice older than four years now almost non-existent compared to its extent in the 1980s. Glaciers worldwide have experienced ice loss for 38 consecutive years, with an average loss equivalent to more than a meter of water for the fourth year in a row.
The report also documented 97 named tropical cyclones during the 2025 storm season, exceeding the 1991–2020 average of 87. This rise in extreme weather events occurs against the backdrop of a rapidly changing climate. One of the report's authors, Robert Dunn from the UK's Met Office, noted that indications of an extremely strong El Niño forming halfway through 2026 could potentially set concerning precursor conditions for the year ahead, given that 2025 was only slightly cooler than 2023 and 2024.