Critical Climate Signals From the UN 2025 Report

The Earth’s climate is more out of balance than at any time in observed history. That is the stark conclusion of the World Meteorological Organisation’s State of the Global Climate report for 2025 – a document that confirms the unprecedented speed and scale of planetary change now underway with consequences that will outlast every living generation.

Released to coincide with World Meteorological Day, the report confirms that 2015–2025 are the hottest 11 years ever recorded, and that 2025 was the second or third hottest year in the 176-year observational record, at approximately 1.43°C above the 1850–1900 pre-industrial average. 

Greenhouse gas concentrations – carbon dioxide, methane, and nitrous oxide – have reached their highest levels in at least 800,000 years, while the annual increase in atmospheric CO₂ in 2024 was the largest single-year rise since modern measurements began in 1957.

For the first time, the report includes Earth’s energy imbalance as a key climate indicator. Under a stable climate, the energy arriving from the sun is roughly balanced by the energy leaving the planet. That equilibrium has been broken. Earth’s energy imbalance reached a new high in 2025, driven by the heat-trapping effect of rising greenhouse gases. And the ocean, as ever, is absorbing the consequences.

More than 91% of the excess heat trapped by greenhouse gases is stored in the ocean, which acts as a vast thermal buffer – absorbing warming that would otherwise be felt on land with far greater ferocity. Ocean heat content reached a new record high in 2025, and its rate of warming has more than doubled from the period 1960–2005 to the period 2005–2025. The ocean is now absorbing the equivalent of about 18 times total annual human energy use every year.

Of the report’s conclusions, Antonio Guterres, UN Secretary General, said: “The State of the Global Climate is in a state of emergency. Planet Earth is being pushed beyond its limits. Every key climate indicator is flashing red.”

Around 90% of the ocean surface experienced at least one marine heatwave in 2025, even amid La Niña conditions that temporarily cool sea-surface temperatures. The ocean has also been absorbing roughly 29% of all CO₂ emitted by human activities since 2015, driving a continued decline in ocean surface pH. Global average ocean surface pH has now fallen over 41 consecutive years, and the IPCC reports with very high confidence that present-day surface pH values are unprecedented for at least 26,000 years.

Meanwhile, the cryosphere paints a no more encouraging picture. Glacier mass loss in the 2024/2025 hydrological year was among the five worst on record, continuing a trend of accelerated loss since 1950 – with eight of the ten worst years occurring since 2016. 

Exceptional glacier loss was recorded in Iceland and along the Pacific coast of North America. Annual Arctic sea-ice extent for 2025 was at or near a record low, and Antarctic sea-ice extent ranked the third lowest after 2023 and 2024. The past four years have produced the four lowest Antarctic sea-ice minima ever recorded.

Global mean sea level, driven by ocean warming and ice melt, stands approximately 11 centimetres higher than when satellite altimetry measurements began in 1993. The rate of rise has accelerated since 2012. The IPCC projects that ocean warming and sea level rise will continue for centuries – and that changes in deep ocean pH are effectively irreversible on centennial to millennial timescales.

Celeste Saulo, WMO Secretary-General, said: “Human activities are increasingly disrupting the natural equilibrium and we will live with these consequences for hundreds and thousands of years.”

The human cost is already being counted. Extreme weather events in 2025 – those such as heatwaves, wildfires, drought, tropical cyclones, storms and flooding – caused thousands of deaths, impacted millions, and generated billions in economic losses. 

Over one-third of the global workforce, some 1.2 billion people, face workplace heat risk at some point each year, particularly those in agriculture and construction. Dengue, the world’s fastest-growing mosquito-borne disease, now puts roughly half the global population at risk, with reported cases at their highest ever recorded.

These rapid and large-scale changes, as the WMO notes, have occurred within just a few decades. Their repercussions, however, will persist for hundreds – and potentially thousands – of years. The question the report does not answer, and cannot answer, is whether the political will to act will arrive before the window to do so closes.

“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,” said Guterres.

“And in this age of war, climate stress is also exposing another truth: our addiction to fossil fuels is destabilising both the climate and global security. Today’s report should come with a warning label: climate chaos is accelerating and delay is deadly,” he concluded.

https://oceanographicmagazine.com/news/every-key-indicator-flashing-red-warns-uns-2025-climate-report/