The amount of heat trapped by the Earth reached record levels in 2025, with the consequences of such warming feared to last for thousands of years, the UN warned Monday.
The 11 hottest years ever recorded were all between 2015 and 2025, the United Nations' WMO weather and climate agency confirmed in its flagship State of the Global Climate annual report.
Last year was the second or third hottest year on record, at about 1.43 Celsius above the 1850-1900 average, the World Meteorological Organization said.
"The global climate is in a state of emergency. Planet Earth is being pushed beyond its limits. Every key climate indicator is flashing red," said UN Secretary-General Antonio Guterres.
"Humanity has just endured the 11 hottest years on record. When history repeats itself 11 times, it is no longer a coincidence. It is a call to act,” AFP quoted him as saying.
For the first time, the WMO climate report includes the planet's energy imbalance: the rate at which energy enters and leaves the Earth system.
Under a stable climate, incoming energy from the Sun is about the same as the amount of outgoing energy, the Geneva-based agency said.
However, the increase in concentrations of heat-trapping greenhouse gases -- carbon dioxide, methane and nitrous oxide -- "to their highest level in at least 800,000 years" has "upset this equilibrium", the WMO said.
"The Earth's energy imbalance has increased since its observational record began in 1960, particularly in the past 20 years. It reached a new high in 2025."
WMO chief Celeste Saulo said scientific advances had improved understanding of the energy imbalance and its implications for the climate.
"Human activities are increasingly disrupting the natural equilibrium and we will live with these consequences for hundreds and thousands of years," she said.
More than 91 percent of the excess heat is stored in the ocean.
"Ocean heat content reached a new record high in 2025 and its rate of warming more than doubled from 1960-2005 to 2005-2025," the WMO said.
Ocean warming has far-reaching consequences, such as degradation of marine ecosystems, biodiversity loss and reduction of the ocean carbon sink, the agency said.
"It fuels tropical and subtropical storms and exacerbates ongoing sea-ice loss in the polar regions."
The Antarctic and Greenland ice sheets have both lost considerable mass, and the annual average extent of Arctic sea ice in 2025 was the lowest or second-lowest ever recorded in the satellite era.
Last year, the global mean sea level was around 11 centimeters higher than when satellite altimetry records began in 1993.
Ocean warming and sea level rise are projected to continue for centuries.
WMO scientific officer John Kennedy said global weather is still under the influence of La Nina, a naturally occurring climate phenomenon that cools surface temperatures in the central and eastern equatorial Pacific Ocean. It brings changes in winds, pressure and rainfall patterns.
Conditions oscillate between La Nina and its warming opposite El Nino, with neutral conditions in between.
The warmest year on record, 2024, was around 1.55C above the 1850-1900 average, and started in a strong El Nino.
Forecasts indicate neutral conditions by the middle of 2026 with a possible El Nino developing before the end of the year, said Kennedy.
If so, "then we're likely to see maybe elevated temperatures again in 2027", he told a press conference.
The World Meteorological Organization's deputy chief, Ko Barrett, said the outlook was a "dire picture".
She said the WMO provided the evidence it sees, hoping that the information "will encourage people to take action".
But there was "no denying" that "these indicators are not moving in a direction that provides for a lot of hope", she said.
With war gripping the Middle East and fuel prices soaring, Guterres said the world should heed the alarm call.
"In this age of war, climate stress is also exposing another truth: our addiction to fossil fuels is destabilizing both the climate and global security," he said.
"Today's report should come with a warning label: climate chaos is accelerating and delay is deadly," he said.
