Chaleur: 7 Alarming Signals from the WMO’s 2025 Climate Report
The planet’s accumulated chaleur reached a record in 2025, the World Meteorological Organization found, a finding that the United Nations calls a climate emergency. The report adds a new metric—Earth’s energy imbalance—to the suite of climate indicators and shows accelerating ocean heating, record greenhouse gas concentrations, and sea level rise that will have effects for hundreds to thousands of years, the agency warns.
Background and context: what the 2025 assessment shows
The WMO places 2025 within a decade of extremes: the years 2015–2025 are the 11 warmest on record, and 2025 ranks among the top two or three warmest years when compared with the 1850–1900 baseline. The global mean surface temperature for 2025 stood about 1. 43°C above that preindustrial reference. For the first time the analysis explicitly includes the planet’s energy imbalance—how much more energy is entering the Earth system than leaving it—and finds that imbalance reached a new high in 2025.
Oceans absorbed the bulk of the excess heat: 91% of the accumulated heat resides in the ocean, and ocean heat content set a new record in 2025. The rate of ocean warming has more than doubled when comparing the 1960–2005 period with 2005–2025. Satellite-era sea level data show a long-term rise that in 2025 measured about 11 cm above the level at the start of satellite records.
Chaleur: what lies beneath the record ocean and atmospheric warming
Greenhouse gases remain central to the observed trends. Record concentrations of carbon dioxide, methane and nitrous oxide were reported in the latest harmonized global dataset for 2024, with indications that levels continued to rise into 2025. That accumulation disrupts the balance between incoming solar energy and outgoing heat, producing an energy surplus in the Earth system and enabling further warming of both ocean and atmosphere.
Physical impacts recorded in 2025 include accelerated glacier and polar ice mass loss, an Arctic sea‑ice extent among the lowest on record, and marine heat stress that affected much of the ocean surface. The WMO summary links ocean warming to degradation of marine ecosystems, loss of biodiversity and a reduced ocean carbon sink, while also noting that warmer seas feed stronger tropical storms and contribute to long‑term sea level rise.
Human vulnerability is already evident: more than one third of the global workforce—about 1. 2 billion people—experienced workplace heat risks during the year, with heightened exposure in sectors such as agriculture and construction. Ocean chemistry shifted as well, with surface pH values that experts say are without precedent in the last tens of thousands of years and with the oceans absorbing nearly 29% of anthropogenic CO2 emissions over a recent multiyear interval.
Expert perspectives and implications
Antonio Guterres, Secretary‑General, United Nations, warned that “the global climate is in a state of emergency. The Earth is being pushed beyond its limits. All key climate indicators are in the red. “
Celeste Saulo, Secretary‑General, World Meteorological Organization, cautioned that “human activities increasingly disrupt the natural balance, and we will have to live with these consequences for hundreds, if not thousands, of years. “
Ko Barrett, Vice‑Secretary‑General, World Meteorological Organization, emphasized the temperature and ocean records, saying the prior year saw an increase of about 1. 43°C above the 1850–1900 reference and that ocean temperatures hit historic highs.
John Kennedy, responsible scientist, World Meteorological Organization, explained the energy imbalance dynamic: in a balanced system incoming solar energy is roughly equal to outgoing energy, but “outgoing energy is reduced due to the increase in greenhouse gas concentrations, and an excess of incoming over outgoing energy means an accumulation of energy in the Earth system. ” He also noted that observational records show the imbalance has intensified since 1960 and especially over the past two decades.
The combination of record chaleur, ocean heating, ice mass loss and rising seas presents cascading risks to coastal ecosystems, freshwater resources and food security, and it erodes the resilience of interconnected economies.
WMO findings also underline the operational need for improved forecasting and early warning capacity: those tools are essential to protect lives and livelihoods from extreme heat, heavy precipitation and tropical cyclones that are already causing disruptions.
As policymakers and communities grapple with these signals, one open question remains: how rapidly can adaptation and early‑warning systems scale to reduce harm while nations confront the long‑term legacy of accumulated chaleur?
