Paris Agreement’s 1.5C Threshold Breach Could Come ‘Earlier Than Expected’, Scientists Warn

Two new studies indicate that we might have already crossed a key threshold to limit global warming in line with the Paris Agreement, after 2024 became the first calendar year where global temperatures surpassed 1.5C.

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The planet might be on track to breach a key global warming threshold “earlier than expected,” two new papers warned on Monday.

The studies, published in Nature Climate Change, follow the hottest year on record and the first in which global temperatures reached 1.5C for the entire year. This has left scientists wondering what this means for warming trends, as it puts us closer to a temperature limit we have pledged to do everything we can to avoid crossing.

Whether the planet has breached the Paris Agreement 1.5C warming target or not is measured over a 20-year retrospective average, meaning last year does not signal a permanent breach. What the new studies investigated, however, is whether we have already entered the 20-year period above 1.5C.

Both concluded we have.

One study, authored by Alex Cannon, a research scientist with Environment and Climate Change Canada, concluded that if 1.5C anomalies continue beyond 18 months, “breaching the Paris Agreement threshold is virtually certain.”

Meanwhile, Emanuele Bevacqua, a climate scientist at the Helmholtz Centre for Environmental Research in Germany, and colleagues put the odds of 2024 being the first year of a 20-year period reaching the 1.5C warming level at “likely” to “virtually certain.”

The Paris deal was drafted in 2015 to strengthen the global response to the growing threat of climate change. It set out a framework for limiting global warming to below 1.5C or “well below 2C” above pre-industrial levels by the end of the century. Beyond this limit, experts warn that critical tipping points will be breached, leading to devastating and potentially irreversible consequences for several vital Earth systems that sustain a hospitable planet.

The United Nations had already estimated that current emissions reduction pledges put the planet on track for a temperature increase of 2.6-3.1C over the course of this century. The only way to avoid this is do drastically reduce greenhouse gas emissions, the primary driver of global warming as they trap heat in the atmosphere, raising Earth’s surface temperature.

Scientists are not optimistic either.

A survey of 380 IPCC scientists conducted by the Guardian last May revealed that 77% of them believe humanity is headed for at least 2.5C of warming.

And on Monday, renowned climatologist James Hansen said even the 2C target “is dead” after his latest paper concluded that Earth’s climate is more sensitive to rising greenhouse gas emissions than previously thought. The former top NASA climate scientist famously announced to the US Congress in 1988 that global warming was underway.⁣

Warming Continues

Hopes that the recent warming trend would subside with the arrival of a cooling weather pattern known as La Niña were dashed last month, as January turned out to be the hottest January ever recorded.

“[M]any of us expect that 2025 will be cooler than both 2023 and 2024, and is unlikely to be the warmest year in the instrumental record,” climatologist Zeke Hausfather wrote in a blog post on Monday. Their expectations were not met, he went on to say, describing how last beat the prior record set in January 2024 “by a sizable margin.”

“January 2025 stands out as anomalous even by the standards of the last two years,” Hausfather wrote. “[A]t least at the start of the year nature seems not to be following our expectations.”

Featured image: Wikimedia Commons.