Informopedia Explains: for years, scientists could say the planet was warming but not prove it was warming faster. A new analysis says that argument is over.
Imagine a car with a speedometer you cannot quite read. For decades, climate scientists knew the planet was moving — temperatures climbing, ice retreating, seas rising — but they could not say with statistical confidence whether it was accelerating. The noise kept getting in the way: a big El Niño here, a volcanic eruption there, a swing in solar output. Strip those out, and a new study argues the needle is now unmistakable.
The number at the centre of it
The analysis, led by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research with statistician Grant Foster, was published in Geophysical Research Letters. It takes five major global temperature records — NASA, NOAA, HadCRUT, Berkeley Earth and ERA5 — and removes the short-term influences of El Niño and its cooler sibling La Niña, volcanic eruptions and solar variation. What is left is the underlying trend. Over the past ten years, that trend runs at about 0.35°C per decade. Between 1970 and 2015 it ran at just under 0.2°C per decade. The recent pace is nearly double, and it is the fastest of any decade since instrumental records began in 1880. The acceleration, the authors say, is visible from around 2013-2014 and clear by about 2015, with more than 98% statistical certainty, consistent across all five datasets and across different statistical methods. “We can now demonstrate a strong and statistically significant acceleration of global warming since around 2015,” Foster said.
Why the usual excuses don’t work this time
The obvious objection is that the last few years were freakishly hot — 2023 and 2024 were the two warmest years on record, juiced by a strong El Niño and a solar maximum. The study accounts for exactly that. Even after removing the El Niño and solar effects, 2023 and 2024 stay the warmest on record in the datasets. The acceleration is not a blip riding on a hot spell; it survives having the hot spell taken out. That is what makes the finding different from earlier claims, which could always be dismissed as weather noise dressed up as trend.
What the study does not say
Here is the honest limit, and the authors state it plainly: the study detects acceleration; it does not assign its causes. It was designed to measure the speedometer, not to open the engine. That distinction matters, because the public debate has already filled the gap with explanations the paper itself does not make. The leading candidate in the wider research is an uncomfortable trade-off: cleaner air. Sulphur particles from fossil fuels once reflected sunlight and brightened clouds, masking some greenhouse warming; as Europe, North America and China cut sulphur emissions, that cooling haze has thinned. Research accounting for natural variation puts the extra warming from cleaner air at roughly 0.05 to 0.1°C per decade, against about 0.2°C per decade from greenhouse gases — a meaningful nudge, not the whole story. Other candidates include the sheer accumulation of greenhouse gases themselves and feedbacks, like darker oceans and ice-free Arctic waters absorbing more heat. None of these is settled by the Potsdam paper, and anyone who tells you otherwise is selling certainty the science has not bought.
What faster warming actually means
A rate is abstract until you translate it. At 0.2°C per decade, the world gains roughly a degree every fifty years. At 0.35°C per decade, it gains one every twenty-eight. Rahmstorf’s warning follows directly: if the pace of the past ten years continues, long-term warming would pass the Paris Agreement’s 1.5°C limit before 2030 — not as a single hot year breaching the line, but as the sustained average crossing it. That pulls forward every deadline built on the slower assumption: adaptation plans, infrastructure design, crop breeding, insurance pricing. It also reframes the politics of the week: COP31 opens in Antalya on Nov 9 with a presidency promising delivery over declarations, and a delivery gap measured in years, not decades, is a different kind of failure.
Why this matters: for years, “is warming accelerating?” was a question scientists answered with caveats. The caveats have now shrunk to a footnote: yes, by the best measurements available, and by a lot. The argument that remains is not about whether the car is speeding up. It is about what is pressing the pedal — and how hard we are willing to brake.
Related coverage on this site: our explainer on El Niño and the temperature records it helped set, and Europe’s record climate finance ahead of COP31.
