Scientists are trying to solve the mystery of whether global warming is speeding up. A new study says it has the answer

By Laura Paddison, CNN

(CNN) — Is the world getting hotter, faster? It’s a big question which has been puzzling and dividing scientists for years. A new paper says it has the answer, and it’s not good news.

Global warming has accelerated “significantly” over the past 10 years, meaning the world may barrel through crucial global warming limits faster than expected, according to the study published Friday in the journal Geophysical Research Letters.

As parts of the Northern Hemisphere recover from very cold blasts, it can be hard to remember just how warm the planet has been over the past few years, but it’s been on an exceptionally hot streak: 2024 was the hottest year on record, capping off the hottest decade in recorded history.

The impacts of all this heat are clear; vast swaths of the world have reeled from devastating climate change-fueled extreme weather including heat waves, hurricanes, wildfires and floods.

But Earth systems are very complex and it is hard to figure out whether a few abnormally hot years means the long-term trend of global warming is speeding up.

In the new paper, scientists looked to answer the question by analyzing five large global temperature data sets and filtering out the “noise” — natural climate variations that have short-term impacts. These include El Niño, volcanic eruptions and the solar cycle, which influence temperatures in the short term, masking long-term changes.

The Earth warmed by about 0.2 degrees Celsius per decade between 1970 and 2015. Then, between 2015 and 2025, it warmed by 0.35 degrees, the study found — a 75% jump.

It’s a “significant” increase and a higher rate than any previous decade since record keeping began in 1880, the paper concluded.

“We think we are the first to show a statistically significant acceleration,” said Stefan Rahmstorf, a study author and head of Earth system analysis at the Potsdam Institute for Climate Impact Research.

Another recent paper co-authored by James Hansen — the US scientist who publicly sounded the alarm on the climate crisis in the 1980s — also concluded global warming is speeding up, but didn’t do a statistical significance test, Rahmstorf said.

Current projections suggest the internationally agreed-upon global warming limit of 1.5 degrees Celsius — which refers to the average over decades not single years — will be breached at some point in the 2030s. But if this accelerated warming rate continues, the world will likely reach 1.5 degrees before 2030, the report found. Past this limit, scientists say the impacts of climate change will start to exceed the ability of humans and ecosystems to adapt.

The study’s methodology is “careful and meticulous,” said Katharine Hayhoe, an atmospheric scientist at Texas Tech University, who was not involved in the research.

Think of the atmosphere like a swimming pool, Hayhoe said. The water is equivalent to carbon dioxide in the atmosphere, and humans have essentially stuck a hose into the pool and every year been turning up the faucet — so the water is rising faster and faster. “In a nutshell, what this study is doing is finally DETECTING what scientists have long PREDICTED,” she wrote in an email.

Claudie Beaulieu, an ocean and Earth sciences assistant professor at the University of California, Santa Cruz, said it was a sign of the study’s accuracy that all five data sets showed an acceleration of warming but pointed to limitations, including how effectively the scientists managed to remove the influence of El Niño, volcanic eruptions and solar changes.

Continued monitoring will be essential to determine if this is “a genuine and lasting shift, or a transient feature of natural variability,” she said.

Others were less convinced. Michael Mann, professor of Earth and environmental science at the University of Pennsylvania, said there’s no evidence of any acceleration in the rate of warming over the past 10 years.

He said warming has been increasing since the 1970s because of decreased aerosol pollution — a type of pollution that’s harmful to human health, but has a cooling impact on the planet as it reflects away the sun’s energy. “There is often a conflation of this well-established fact with the notion that there is a recent increase in the rate of warming over the past decade,” he said. The heat spikes over the last few years were due to El Niño, he said.

“The planet is warming at a roughly constant rate and that’s bad enough. It will continue to do so until carbon emissions reach zero,” Mann added.

On that final point, he and Rahmstorf are in agreement. Despite scientific consensus on climate change and increasing real-world evidence of the deadly price of living on a hotter planet, there is a “backlash” against climate action, Rahmstorf said. This is especially true in the US, “where the government basically just denies reality,” he added.

Rahmstorf was a young scientist in the 1990s, at a time when the facts of climate change started to become clear.

“I just could not have imagined that policymakers would get such clear evidence that we are heading into a very serious disaster for humanity and not act,” he said.

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