The WMO, the UN agency for weather and climate, published its State of the Global Climate 2025 report in March 2026. The report finds that 2025 was 1.43°C, plus or minus 0.13°C, above the 1850 to 1900 average, making it the second or third warmest year on record depending on the dataset. The 11 years from 2015 to 2025 were the 11 warmest in the observational record.
The WMO combines several international temperature datasets, which is why its estimate differs slightly from the 1.47°C reported by the Copernicus Climate Change Service in January. Both agree that 2025 was below the record set in 2024 but among the three warmest years observed.
Record ocean heat
The report finds that ocean heat content reached a new record high in 2025. Between 2005 and 2025, the ocean gained heat at a rate of 11.0 to 12.2 zettajoules a year, which the WMO compares to about 18 times annual human energy use. About 91% of the excess energy trapped in the climate system goes into the ocean.
The WMO also reports that the Earth's energy imbalance, the difference between incoming energy from the sun and outgoing energy to space, reached its highest level in the 65-year observational record. The energy imbalance is a direct measure of how quickly the climate system is accumulating heat.
Sea ice
Arctic sea ice extent averaged 10.10 million square kilometres in 2025, and Antarctic sea ice averaged 10.81 million square kilometres, according to the report. Both are well below long-term averages. Antarctic sea ice has been unusually low since 2023 after decades of relative stability.
Why ocean heat matters for energy
Ocean heat affects energy systems in several ways. Warmer oceans supply more energy to tropical cyclones, which can intensify rapidly over warm water. Hurricane Melissa, which hit Jamaica in October 2025 as a Category 5 storm, caused extensive damage to the island's power grid. In the Gulf of Mexico, hurricanes affect offshore oil and gas production, refineries and LNG export terminals.
Warm seas also affect power plants that use seawater for cooling. Coastal nuclear and thermal plants can face output limits when water temperatures rise, though these are less common than for river-cooled plants. Marine heatwaves can affect offshore wind farms indirectly, through changes in wind patterns and sea conditions, and they affect the fisheries and ecosystems near which offshore energy infrastructure is built.
Sea level rise, driven by ocean warming and melting ice, poses long-term risks to coastal energy infrastructure, including ports, refineries, LNG terminals and power stations. Many of the world's largest energy facilities are located on coastlines.
Extreme events in 2025
The report reviews extreme events that affected people and economies during the year. These included heatwaves across Asia, Europe and North America, floods in South Asia, including the monsoon floods in Pakistan, and wildfires, including the January fires in Los Angeles. Each of these had direct effects on energy systems. Heatwaves pushed electricity demand to records in several countries, floods damaged power infrastructure, and the Los Angeles fires raised questions about utility liability for wildfire ignitions.
The 1.5°C question
The report discusses the Paris Agreement goal of limiting warming to 1.5°C. The WMO notes that individual years above 1.5°C do not mean the long-term goal has been missed, because the goal refers to warming averaged over about two decades. Its estimates of current long-term warming are around 1.3°C to 1.4°C. The WMO and other agencies have said that the remaining carbon budget for 1.5°C is small, and that on current trends the long-term average is likely to reach that level within the next decade.
What it means for energy planning
For energy companies, the WMO indicators provide context for planning assumptions. Demand forecasts depend on temperature, and the trend towards hotter summers increases peak electricity demand for cooling. Supply forecasts depend on water availability for hydropower and cooling. Infrastructure design standards for transmission lines, substations and pipelines are often based on historical climate data that may no longer reflect current conditions.
Utilities, insurers and investors increasingly use climate scenarios to assess physical risks to assets. The financial sector uses scenarios from the Network for Greening the Financial System, and many companies report climate risks under frameworks based on the Task Force on Climate-related Financial Disclosures, now absorbed into the International Sustainability Standards Board's standards.
Precipitation extremes
The report also documents heavy rainfall and drought. Both affect hydropower, which supplies a large share of electricity in Brazil, Canada, Norway, China and much of Africa and South Asia. Years of low rainfall reduce output and force systems to burn more fossil fuels, while floods can damage dams and transmission.
Early warning
The WMO has also been leading the UN's Early Warnings for All initiative, which aims to ensure everyone on earth is covered by early warning systems for hazardous weather. The report notes that many countries still lack comprehensive warning systems. For energy systems, early warning of storms, heatwaves and floods allows grid operators to prepare, position repair crews and adjust generation.
Glaciers and water supply
The report also tracks glacier mass loss, which continued in 2025. Glaciers feed rivers that supply hydropower and cooling water in the Alps, the Andes, Central Asia and the Himalayas. Pakistan's Indus system depends heavily on glacier and snow melt from the Karakoram and Himalayas. In the short term, faster melting can increase summer river flows, but over decades the loss of glacier volume reduces the water available in dry seasons. Hydropower operators and grid planners in these regions are beginning to factor long-term glacier decline into their outlooks.
Data quality and continuity
The report draws on national meteorological services, satellite agencies and research institutions. Continuity of observation networks matters for energy markets, which use weather data for trading, forecasting and risk management. Budget cuts at some national agencies, including in the United States, have raised concerns among scientists about gaps in long-term records.
What to watch
The WMO's annual-to-decadal forecasts, published in late spring, provide probabilities for temperatures over the next five years. Seasonal outlooks for the northern hemisphere summer will indicate likely demand conditions in key power markets. Forecasters are watching for a possible return of El Niño later in 2026, which would raise the chances of record global temperatures in 2027.