In a first, researchers confirm global warming has accelerated in last decade

AGU press contact:
Sean Cummings, [email protected] (UTC-8 hours)

Researcher contact: 
Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, [email protected] (UTC+1 hours)

WASHINGTON - For the first time, scientists have stated with statistical confidence that global warming is accelerating, not merely continuing at a steady pace. According to a new study, the past decade ranks as the fastest-warming on record. At the current pace, the authors wrote, Earth will exceed the limit of 1.5 degrees Celsius of warming set by the Paris Climate Accord before 2030.

Although the finding is not unexpected, its level of certainty sets it apart from previous research.

The study appears in Geophysical Research Letters, AGU's journal for high-impact, innovative, and timely articles on major advances across the geosciences.

"We can now demonstrate a strong and statistically significant acceleration of global warming since around 2015," said Grant Foster, a retired statistician formerly at Tempo Analytics and co-author of the study.

BENEATH THE NOISE, A SPEEDING HEATING

Up to now, most analyses of global warming have indicated a fairly steady rise in the average global temperature of about 0.2 degrees Celsius per decade since the 1970s. Recently, however, scientists have begun debating whether the pace of warming has accelerated since then, in part due to exceptionally high average global temperatures in recent years, said Stefan Rahmstorf, a climate scientist at the Potsdam Institute for Climate Impact Research and coauthor of the study.

Research within the past few years has hinted at possible acceleration, but natural fluctuations in global temperature due to forces like El Niño and volcanism have made it difficult to confirm with statistical significance. Natural variation has created a false impression in the past, in particular after the strong 1998 El Niño event, which provoked speculation that overall warming had slowed or even stopped. Accounting for this variation was one way the same authors had shown this temporary slowdown to be insignificant, Rahmstorf said.

The duo took a similar tack to examine the possibility of accelerated warming, estimating the impact from three major factors: El Niño events, volcanic eruptions, and variations in radiation from the sun.

"We filter out known natural influences in the observational data, so that the 'noise' is reduced, making the underlying long-term warming signal more clearly visible," Foster explained.

This revealed a near-doubling in the rate of warming, reaching up to around 0.35 degrees per decade beginning around 2015. The result held true across all five of the global temperature datasets the duo considered, including those from NASA and NOAA. Notably, their analysis included 2023 and 2024, the two hottest years on record, meaning the acceleration still appears even after accounting for the effect of El Niño in these outlier years.

Scientists had expected some acceleration. The finding aligns with the warming scenarios put forth previously in the sixth Assessment Report by the Intergovernmental Panel on Climate Change.

"Climate models have a relatively broad uncertainty range, and we're still within that," Rahmstorf said, but even so, an acceleration this drastic "is a bit unexpected."

If sustained, the acceleration would also push Earth past the Paris Agreement limit of 1.5 degrees Celsius of warming over preindustrial levels before 2030, several years earlier than previous estimates. This may not occur if the past decade turns out to be an outlier, Rahmstorf said, but "2030 is in four years' time. The current rate doesn't need to continue long, and then we're above 1.5."

IT'S IN OUR HANDS

The cause of the acceleration remains unsettled, but the leading theory, the researchers wrote, attributes it largely to a reduction in air pollution in the atmosphere. These floating aerosols, produced mainly through fossil-fuel-burning activities, absorb and reflect sunlight and promote cloud cover and brightness, thereby masking some of the warming also caused by fossil fuel burning. However, successful efforts to improve air quality have made them less abundant since the early 2000s, a factor climate models may not sufficiently account for, Rahmstorf said. If aerosol reduction is indeed the key driver, then warming would slow down again if aerosol reductions slow down - though given the negative health impacts of aerosols, this is not recommended, he added.

Whatever its cause, the acceleration in warming highlights the insufficiency of current efforts to halt it, the duo wrote, and the current political climate raises the possibility that warming will accelerate further.

"We are not doing enough in terms of climate policy. We see this terrible rollback in the United States and, to a lesser extent, in Germany," Rahmstorf said. "How quickly the Earth continues to warm ultimately depends on how rapidly we reduce global CO₂ emissions from fossil fuels to zero."

Continued warming will ratchet up the threats to health and livelihood people around the world face from rising sea level, heat stress, disease, natural disasters, and many other factors. "Stopping this trend is in our hands," the researchers wrote.

Notes for journalists:

This study is published in Geophysical Research Letters, an open access AGU journal. View and download a PDF of the study here. Neither this press release nor the study is under embargo.

Paper title:

"Global Warming has Accelerated Significantly"

Authors:

• Grant Foster, retired, Orono, Maine, United States

• Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Potsdam, Germany

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