The rate at which the planet is warming has roughly doubled, according to a study in Geophysical Research Letters, which puts warming over the past ten years at about 0.35C per decade against an average of just under 0.2C per decade between 1970 and 2015.
The paper, titled “Global Warming Has Accelerated Significantly”, is by Grant Foster, a statistics expert in the United States, and Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, which issued the announcement carried by ScienceDaily.
The authors removed known natural influences from the temperature record — El Niño, volcanic aerosols and the roughly 11-year solar cycle — in order to isolate the underlying trend. “We filter out known natural influences in the observational data, so that the ‘noise’ is reduced,” Foster said.
Two statistical approaches were applied to five datasets, those of NASA, NOAA, HadCRUT, Berkeley Earth and ERA5. A quadratic trend analysis tested whether the curve was bending; a piecewise linear model let the data determine when the rate changed rather than assuming a date in advance. Both approaches supported acceleration.
“We can now demonstrate a strong and statistically significant acceleration of global warming since around 2015,” Foster said. Signs of the change appear in 2013 or 2014 across all five datasets.
“The adjusted data show an acceleration of global warming since 2015 with a statistical certainty of over 98 percent,” Rahmstorf said. After adjustment, 2023 and 2024 remained the warmest years in an instrumental record that begins in 1880, although their adjusted values came out somewhat lower than the originals.
“If the warming rate of the past 10 years continues, it would lead to a long-term exceedance of the 1.5°C limit,” Rahmstorf said, referring to the Paris Agreement threshold, which concerns sustained long-term warming rather than any single hot year. He added that “how quickly the Earth continues to warm ultimately depends on how rapidly we reduce global CO2 emissions”.
The study detects a change in the rate and was not designed to identify its physical causes. The authors note that the acceleration is consistent with what current climate models can produce, and that the precise figure depends on which temperature dataset is used.
The methodological achievement here is easy to miss. For thirty years the public argument has been about a number. This paper is about that number’s rate of change, which means the argument has been promoted.
There is a first derivative now, officially, with a confidence level attached to it. Temperature is no longer the quantity of interest. The quantity of interest is how quickly temperature is becoming a different quantity.
Our analysts, who have waited years for a development of this kind, point out what must follow. If the rate of warming can accelerate, then the acceleration can itself accelerate, and the paper’s own quadratic term is an invitation that no newspaper should decline.
The Department of Unnecessary Research has accordingly opened a file on the third derivative. It will establish whether the acceleration is becoming more acceleration-like, a quantity for which no agency currently operates a monitoring network and which is therefore entirely unconstrained by observation.
The practical consequence is a change of unit. Warming used to be reported in degrees. It is now properly reported in degrees per decade, and will shortly be reported in degrees per decade per decade.
The authors, for the record, were careful to say that their analysis identifies a change in rate and not its cause. That restraint will not survive the unit. A figure given in degrees per decade per decade cannot be felt, cannot be checked by stepping outside, and can therefore be disputed by nobody.