A new international assessment of Earth’s climate has delivered a stark message: the planet’s major climate indicators continued to deteriorate in 2025, with greenhouse gas concentrations, ocean heat content, and global sea level all reaching record highs. The findings come from the 36th annual State of the Climate report, published by the American Meteorological Society and compiled by 625 scientists from 60 countries. Drawing on measurements from weather stations, ocean instruments, satellites, aircraft, ice monitoring systems, and other observing networks, the report provides one of the most detailed annual snapshots of the changing climate system.
Atmospheric carbon dioxide, methane, and nitrous oxide all reached their highest recorded concentrations during the year. The globally averaged carbon dioxide concentration rose to 425.6 parts per million, with an uncertainty of approximately 0.1 parts per million. That level is about 53% higher than the estimated preindustrial concentration of 278 parts per million. Fossil fuel emissions also reached a new record, estimated at 10.3 petagrams of carbon per year, more than three times the annual level recorded during the 1960s. These gases trap outgoing infrared radiation, increasing the energy retained within the atmosphere, oceans, land, and ice.
Global temperatures remained exceptionally high even though the tropical Pacific did not experience a conventional El Niño event. The average temperature across Earth’s land and ocean surfaces ranked among the three warmest in records extending back to the mid-1800s. All five major global temperature datasets examined by the report agreed that the period from 2015 through 2025 contained the 11 warmest years ever measured. Europe experienced its warmest year on record, while Russia, China, the Republic of Korea, and Argentina each recorded their second-warmest year. The result makes 2025 the warmest year observed without El Niño conditions dominating the Pacific.
Sea surface temperatures were similarly unusual. Although cool ENSO conditions and weak La Niña patterns affected the equatorial Pacific during parts of the year, the global annual sea surface temperature was the third highest in the 172-year observational record. It stood approximately 0.38 degrees Celsius above the 1991–2020 average. Marine heat waves affected about 87% of the world’s ocean surface at least once during 2025, while only 26% experienced a marine cold spell. Such heat extremes can disrupt fisheries, damage coral reefs, alter marine food webs, and intensify evaporation, providing additional moisture and energy for some storms.
The ocean continued to act as Earth’s largest absorber of excess heat. Over roughly the past 50 years, the oceans have taken up nearly 90% of the additional energy trapped by greenhouse gases and other climate influences. Measurements extending from the surface to a depth of 2,000 meters showed that global ocean heat content reached another record in 2025. As seawater warms, it expands through thermal expansion, while melting glaciers and ice sheets add water to the ocean. Together, these processes pushed global mean sea level to a record for the 14th consecutive year, approximately 111.2 millimeters above the 1993 satellite-altimetry baseline.
The polar regions again showed some of the clearest signs of accelerated warming. The Arctic experienced its second-warmest year in a 126-year record, with surface air temperatures rising at roughly three times the global average rate. Increasing warmth and precipitation contributed to greater tundra vegetation, and Arctic greenness reached the third-highest level in the record. Yet sea ice continued to shrink. The Arctic’s maximum annual sea-ice extent was the lowest in 47 years of satellite observations, while the minimum was the 11th lowest. Ice older than four years, which is generally thicker and more resistant to melting, has nearly disappeared. In September 2025, only about 95,000 square kilometers of such ice remained, compared with approximately 1.5 million square kilometers during the 1980s.
Antarctica also recorded its warmest year since continuous records began in 1979. Surface melting exceeded average levels across most Antarctic ice shelves, and melting on the Antarctic Peninsula approached record values in early January. Sea ice surrounding the continent remained below average, continuing a nearly decade-long period of unusually low coverage. The annual maximum and minimum sea-ice extents ranked as the third and fourth lowest, respectively. Meanwhile, land-based glaciers worldwide lost ice for the 38th consecutive year. Their average loss exceeded one meter of water equivalent for the fourth year in a row, and approximately 41% of the total ice loss recorded since 1976 occurred during the last decade.
The atmosphere’s increasing heat and moisture were accompanied by an active tropical cyclone year. Ninety-seven named tropical cyclones formed across the Northern and Southern Hemisphere storm seasons, compared with a 1991–2020 average of 87. Five reached Category 5 intensity. Hurricane Melissa became one of the strongest Atlantic hurricanes ever recorded, reaching maximum winds of 190 miles per hour and a minimum central pressure of 892 hectopascals on October 28. It struck Jamaica as a Category 5 storm, causing severe destruction in the western part of the island, 95 reported deaths, and at least $12.2 billion in damage. In the Australian basin, 12 named storms formed during the 2024–25 season, the highest seasonal total since 2005–06. Tropical Cyclone Zelia reached Category 5 strength over the ocean before making landfall in Western Australia as a Category 4 storm.
The report’s findings do not describe isolated changes in a single part of the planet, but a connected shift across the climate system. Greenhouse gases are increasing the atmosphere’s heat-trapping capacity; the ocean is accumulating energy; sea level is rising; glaciers and polar ice are shrinking; and extreme heat and powerful storms are affecting ecosystems and communities. Because the State of the Climate is peer-reviewed and assembled from independent monitoring systems around the world, its value lies not only in individual records but in the consistency of the overall signal. The measurements show that Earth’s climate continued moving into unfamiliar territory in 2025, even during a year without a strong El Niño.
Subject of Research: Earth’s climate system, including greenhouse gases, global temperatures, oceans, sea level, polar regions, glaciers, and tropical cyclones.
Web References: State of the Climate report
References: State of the Climate in 2025, special supplement to the Bulletin of the American Meteorological Society, Vol. 107, No. 8, August 2026.
Image Credits: Figure 1.1 in the State of the Climate in 2025, special supplement to the Bulletin of the American Meteorological Society, Vol. 107, No. 8, August 2026.
Keywords: Climate change, global warming, greenhouse gases, carbon dioxide, ocean heat, sea-level rise, Arctic, Antarctica, glaciers, sea ice, marine heat waves, tropical cyclones, La Niña, climate monitoring.
