1464. The Earth's Climate Is Becoming Increasingly Unbalanced

According to a report by the World Meteorological Organization (WMO), the 11 years from 2015 to 2025 were the hottest years on record. 2025 was confirmed to be the second or third hottest year on record, exceeding the average temperature from 1850 to 1900 by approximately 1.43°C. Extreme weather events such as heat waves, torrential rains, and tropical cyclones around the world caused immense damage, highlighting economic and social vulnerabilities.

Data from individual observation sites indicate that concentrations of the three major greenhouse gases—carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—continued to rise in 2025. In 2024 (the last year for which global observational data were integrated), atmospheric CO2 concentrations reached their highest level in the last two million years, while CH4 and N2O oxide concentrations reached their highest levels in at least the last 800,000 years. The annual increase in CO2 concentration in 2024 was the largest annual increase since modern observations began in 1957. This is due to the continued emission of CO2 from fossil fuels and the declining effectiveness of carbon sinks on land and in the ocean.

This report, for the first time, addresses the Earth's energy balance as one of its key climate indicators. The Earth's energy balance is an indicator that measures the amount of energy entering and leaving the Earth system. In a stable climate, the energy entering from the sun is roughly equal to the energy leaving the Earth. However, this balance has been disrupted by the fact that concentrations of greenhouse gases such as CO2, CH4, and N2O have reached levels not seen in at least 800,000 years. The Earth's energy balance has been increasing since observations began in 1960, particularly over the past 20 years, reaching a record high in 2025.

Atmospheric warming, including near the Earth's surface (temperatures perceived by humans), accounts for only 1% of the excess energy; approximately 5% is stored in continents. Over 91% of the excess heat is stored in the oceans, which act as a major buffer against rising land temperatures. Furthermore, 3% of the excess energy is warming and melting ice. Both the Antarctic and Greenland ice sheets have lost significant mass, and the average annual sea ice area in the Arctic Ocean in 2025 will be the lowest or second lowest on record according to satellite observations. In 2025, unusual mass reductions in glaciers were observed in Iceland and along the Pacific coast of North America.

Warming oceans and melting ice are driving a long-term rise in the global mean sea level, a rise that has accelerated since satellite observations began in 1993. According to projections by the Intergovernmental Panel on Climate Change (IPCC), ocean warming and sea level rise are expected to continue for several centuries. Ocean warming and changes in deep-sea pH are irreversible on a timescale of 100 to 1000 years.

(Reference)
WMO (2026) State of the Global Climate 2025, WMO-No. 1391. https://library.wmo.int/records/item/69807-state-of-the-global-climate-…

Contributor: IIYAMA Miyuki, Information Program