Global climate data for 2025 paint a stark picture of a world now firmly in a new thermal regime. The Copernicus Climate Change Service finds that 2025 was the third warmest year on record, extending an eleven‑year run in which every year has been unprecedentedly hot.
A hotter new normal
Copernicus estimates that global surface air temperature in 2025 was 1.47°C above the pre‑industrial baseline, only slightly below 2023 and just 0.13°C cooler than 2024, the warmest year on record. When averaged over 2023–2025, temperatures now exceed 1.5°C above pre‑industrial levels, the first time any three‑year period has crossed this symbolic threshold.
Using several approaches, scientists judge long‑term warming to be around 1.4°C above pre‑industrial conditions. On present trends the Paris Agreement’s 1.5°C limit for long‑term warming could be reached before 2030, more than a decade earlier than envisaged when the deal was signed.
Land, poles and oceans
Air temperatures over global land areas in 2025 were the second highest on record, underlining the particular vulnerability of continental regions. The Antarctic registered its warmest year yet, while the Arctic experienced its second warmest year, continuing the well‑known pattern of amplified polar warming.
The oceans also tell an unsettling story. Global sea‑surface temperature outside the polar regions reached 20.73°C, the third highest value after 2024 and 2023, reflecting exceptional marine heat. Across much of the globe, both air and sea temperatures remained well above the late twentieth‑century norm, despite somewhat less extreme warmth in parts of the tropics than in the previous two years.
El Niño, La Niña and human influence
The exceptional warmth of 2023–2025 has two principal causes. First, the continued accumulation of greenhouse gases, exacerbated by a reduced capacity of natural sinks to absorb carbon dioxide. Secondly, very high sea‑surface temperatures, linked to a strong El Niño in 2023–2024 and other ocean variability, have been amplified by human‑driven climate change.
Conditions in 2025 shifted towards ENSO‑neutral or weak La Niña in the equatorial Pacific, which tends to cool the global mean slightly. Yet even with this moderating influence, global temperatures remained extraordinarily high, emphasising that natural variability now rides on top of a much warmer baseline.
Heat, wildfires and human health
For roughly half of the world’s land surface, 2025 brought more days than average with at least strong heat stress, defined as a feels‑like temperature of 32°C or higher. Heat stress is recognised by the World Health Organization as the leading cause of weather‑related mortality, turning statistical anomalies into direct threats to human life.
Persistent heat also primed landscapes for fire. Parts of Europe registered their highest annual wildfire emissions on record, with notable events in Spain, while large fires burned in Canada and Southern California. According to Copernicus Atmosphere Monitoring Service data, these fires injected carbon, particulate matter and ozone precursors into the atmosphere, degrading air quality far beyond the immediate burn zones.
Shrinking ice and a narrowing window
The cryosphere offers another line of evidence for a rapidly changing climate. In February 2025, the combined sea‑ice cover of the Arctic and Antarctic fell to its lowest extent in the satellite era. Arctic sea ice set record monthly lows for January, February, March and December, with March bringing the smallest annual maximum yet observed.
Antarctic sea ice was scarcely more reassuring, with the fourth‑lowest annual minimum in February and the third‑lowest maximum in September. These losses matter because sea ice helps regulate planetary energy balance and supports fragile polar ecosystems, so its retreat signals structural changes in both physics and biology.
Evidence, responsibility and resilience
The convergence of indicators leaves little room for complacency. Senior scientists at Copernicus and ECMWF emphasise that the last eleven years being the warmest on record is further, unmistakable evidence of a hotter climate, driven primarily by rising atmospheric greenhouse gas concentrations from human activities. Atmospheric monitoring by the Copernicus Atmosphere Monitoring Service shows these gases have increased steadily over the past decade, underscoring that the atmosphere is, in their words, “sending us a message”.
Policymakers now face a dual task. Mitigation remains essential to limit the scale and duration of any overshoot of Paris targets, while adaptation becomes ever more urgent as extremes in heat, storms and fire shift from outliers to expectations. The quiet but indispensable work of climate monitoring services such as Copernicus provides the empirical foundation on which any rational response must rest.
Are we already past 1.5°C?
The world has now spent multiple years close to or above 1.5ºC of warming when measured over short periods, and the long‑term average is rapidly converging on that threshold. In practice, keeping warming “well below” 1.5ºC without any overshoot is no longer realistic under current policies and emission trends.
It is important, though, to be precise about what is meant by “past the point of return”. In the Paris Agreement, the 1.5ºC goal refers to long‑term human‑induced warming, averaged over decades, rather than a single hot year or even a brief multi‑year breach. From a geophysical standpoint, scenarios still exist in which very rapid emissions cuts, followed by large‑scale net‑negative emissions, could bring temperatures back towards 1.5ºC after an overshoot, though they are now highly demanding and politically implausible.
The underlying difficulty is that atmospheric greenhouse gas concentrations are still rising. CO₂, methane and nitrous oxide are all at record highs, shrinking the remaining carbon budget to a few years at today’s emission rates. Even if emissions were stabilised, the climate system has not yet caught up with the forcing already applied, so “committed” warming will continue as the oceans and ice sheets adjust over decades to centuries.
At current greenhouse gas levels, the eventual equilibrium warming would be noticeably higher than the warming already experienced, implying that simply freezing concentrations where they are would still take us beyond 1.5ºC in the long run. Moreover, as air pollution is reduced, the cooling effect of aerosols will diminish, unmasking some additional warming that is currently being held in check. In this sense the system is primed for further heating unless emissions fall very quickly and then go net‑negative.
Overshoot, irreversibility and hysteresis
Overshooting 1.5ºC, even temporarily, is not just a detour that can be undone at leisure. A growing body of work on tipping elements shows that every additional 0.1ºC of overshoot raises the risk of triggering abrupt changes in systems such as ice sheets, major ocean currents and the Amazon rainforest. If these thresholds are crossed, parts of the Earth system can shift into new states that do not simply reverse when temperatures later decline.
This is where hysteresis comes in. The pathway to a cooler world is not the same as the pathway that took us to a hotter one, because processes like ice‑sheet collapse, coral bleaching or species extinction have their own internal momentum and timescales. Studies of polar ice indicate that even sustaining today’s warming could commit us to metres of sea‑level rise over coming centuries, and temporary excursions above 1.5ºC further increase that commitment, even if temperatures are later brought down. In short, overshoot is not harmless: it can leave a legacy of irreversible loss in ice, ecosystems and biodiversity that no subsequent return to 1.5ºC can fully repair.