The Brief

A study published in Geophysical Research Letters by researchers at the Potsdam Institute for Climate Impact Research has found, with over 98 percent statistical confidence, that global warming has nearly doubled in pace since 2015 — rising at roughly 0.35°C per decade compared to under 0.2°C from 1970 to 2015. If the current rate holds, the Paris Agreement’s 1.5°C limit will be permanently breached before the end of this decade.

The Report

Researchers Stefan Rahmstorf and Grant Foster have published the first peer-reviewed confirmation that the rate of global warming has accelerated significantly over the past decade, with temperatures rising at approximately 0.35°C per decade since 2015 — nearly double the 0.2°C rate that held from 1970 to 2015.

The study, published in Geophysical Research Letters, analysed five independent global temperature datasets — NASA, NOAA, HadCRUT, Berkeley Earth, and the Copernicus ERA5 reanalysis — and found statistically significant acceleration across all of them. The researchers’ method involved stripping out the effects of El Niño cycles, volcanic eruptions, and solar variability before testing for a trend change, reducing the noise that had previously prevented earlier studies from reaching firm conclusions. The change-point detection placed the onset of acceleration between February 2013 and February 2014.

A 2024 study led by Claudie Beaulieu at UC Santa Cruz applied the same statistical test to raw temperature records without first removing natural variability and concluded that acceleration was “not detectable yet.” Foster described that work as “excellent” but noted the difference: with natural signals filtered out, “acceleration is easy to prove statistically — some might even say it becomes obvious.”

The finding is not without dissent. Michael Mann, professor of Earth and Environmental Science at the University of Pennsylvania, maintains there is “no evidence of any acceleration in the rate of warming over the past 10 years,” attributing the apparent increase to decreased aerosol pollution and El Niño. Piers Forster, lead author of the Indicators of Global Climate Change report, which calculated a lower warming rate of 0.27°C per decade over 2015–2024, said he prefers the term “unprecedented rates of warming” to “accelerating,” calling the latter “emotive, but difficult mathematically.” Zeke Hausfather noted that removing El Niño effects from surface records “is more of an art than a science.”

The leading explanation for the acceleration centres on reduced atmospheric aerosol pollution — particularly the International Maritime Organization’s 2020 regulation capping sulfur content in shipping fuel, which removed approximately 8.5 megatonnes of annual sulfur dioxide emissions. Those pollutants had previously formed reflective clouds that masked underlying warming. Rahmstorf himself caveated that “this high warming rate may not continue in the next decade, because no similar big reduction in aerosols would be expected.”

The projections, however, are stark. Depending on the dataset, the study places permanent breach of the 1.5°C Paris Agreement threshold between 2026 and 2029. Global fossil fuel CO₂ emissions reached a record 38.1 billion tonnes in 2025, with atmospheric concentrations hitting 425.7 parts per million — 52 percent above pre-industrial levels. The remaining carbon budget for 1.5°C stands at approximately 170 billion tonnes, equivalent to roughly four years at current emission rates.

The Angle

The most revealing feature of this study is not the headline number. It is the methodological dispute underneath it — and what that dispute actually measures.

The raw temperature record, unfiltered, was not enough to prove acceleration. A 2024 study using the same statistical test on the same data found the signal fell short of significance. What Foster and Rahmstorf did differently was subtract the noise — ENSO, volcanic aerosols, solar variation — before running the test. The signal that emerged was unambiguous across five independent datasets. The question this raises is not whether the method is valid. It is why the planet’s temperature record has become so noisy that a near-doubling in the warming rate can hide inside natural variability for a decade before the statistics catch up.

The aerosol explanation deserves more scrutiny than it is receiving. The IMO 2020 shipping regulation removed sulfur pollution that had been inadvertently cooling the planet — a regulation designed to improve air quality that also stripped away a thin, accidental layer of climate insulation. The warming it unmasked was already there; the aerosols were simply hiding it. The implication is that decades of industrial pollution were performing a function no one designed and no one accounted for, and when standard environmental regulation removed it, the underlying rate of warming was revealed to be significantly worse than the observed trend suggested. The planet was not warming at 0.2°C per decade. It was warming at 0.2°C per decade minus whatever the aerosols were subtracting. The clean-air regulations did not cause the acceleration. They revealed the bill.

Rahmstorf’s own caveat — that the rate may not continue because no comparable aerosol reduction is forthcoming — is reassuring only if the aerosol unmasking is the sole driver. If rising emissions and weakening carbon sinks contribute independently, the caveat narrows. Fossil fuel CO₂ hit a record in 2025. The remaining budget for 1.5°C is four years of current output. The debate over whether to call this “acceleration” or “unprecedented rates” is a question about vocabulary. The trajectory underneath it is the same either way.

The 1.5°C threshold was set in Paris in 2015. At the time, breach was projected around 2045. The current range is 2026 to 2029. The target did not move. The ground did.