There have long been indications that global warming has accelerated in recent years. Climate researchers have now examined this in more detail using two different statistical methods and have also taken possible disruptive effects such as El Niño, solar activity and volcanic eruptions into account. The result confirms that global warming has accelerated significantly since around 2015 – from 0.2 degrees per decade in the long-term average from 1970 to 2015 to 0.35 degrees per decade since 2015. This means that the climate change curve shows a clear upward bend. The reasons for this have only been partially clarified, but one reason is considered to be the reduced air pollution, especially over Asia.
Climate change and its consequences can now hardly be overlooked: greenhouse gas levels in the earth’s atmosphere have reached record levels, and the CO2 content alone is 412 ppm, higher than ever measured before. The atmosphere, land areas and oceans have heated up to record temperatures in recent years and extreme weather events are also continuing to increase. Studies also show that the earth’s radiation balance – the ratio of the energy radiated in by the sun and the heat released back into space – is now more out of balance than the models can understand. In this context, climate researchers have been discussing the rate of global warming for some time: Is it largely linear or has it accelerated?
Five data sets and two different statistical methods
“Since the 1970s, the global trend in mean surface temperatures has followed a relatively steady upward trend: temperatures rose – despite constant fluctuations around this trend – at an average rate of around 0.2 degrees per decade,” explain US statistician Grant Foster and climate researcher Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research (PIK). But recently this rate of warming appears to have increased. How strong this effect is and whether it is just due to natural fluctuations was, however, controversial. The analyzes produced contradictory results. That’s why Foster and Rahmstorf examined this possible acceleration again in more detail. As a basis, they used temperature data from five different, internationally established data sets, including from NASA, the US Atmospheric Agency NOAA and the Copernicus Climate Change Service in Europe.
In order to reduce disruptive effects, the researchers first calculated short-term natural fluctuations caused by El Niño, volcanic eruptions and the cycles of solar activity from this raw data. Their effects overshadow the long-term trend. “It is crucial that we remove these known, natural fluctuations from the measurement data, so that the random ‘noise’ is reduced and the long-term warming signal becomes clearer,” explains Foster. To test whether the rate of warming has changed since the 1970s, the researchers used two different statistical approaches: The first assumes that warming has changed since the 1970s as a quadratic function of time. The second analysis is based on a piecewise linear model. This divides time into ten-year periods and attempts to assign a linear slope to each period.
Faster warming since 2015
The result: “The adjusted data show an acceleration of global warming since 2015 with a statistical certainty of over 98 percent, consistent in all data sets examined and independent of the evaluation method chosen,” reports Rahmstorf. According to this, the warming rate determined over the past ten years was around 0.35 degrees Celsius per decade. The long-term average from 1970 to 2015, however, is just under 0.2 degrees per decade. This upward bend in the climate curve was evident in all five data series and in all statistical approaches used, as the team emphasizes. “We can now demonstrate for the first time a strong and statistically significant acceleration of global warming after 2015,” says Foster.
This accelerated warming was still noticeable even when the researchers calculated out the heating effect of El Niño and the solar maximum, which contributed significantly to warming, especially in 2023 and 2024. After this correction, both years became cooler, but remained the two warmest since measurements began. “This is strong evidence that the statistical significance for accelerated warming is not due to these two outlier years, but rather that global temperature has deviated from its previous path since around 2015,” Foster and Rahmstorf write. The results confirmed that the Earth has warmed faster in the last ten years than in any previous decade since measurements began in 1880.
Air pollution as a contributing cause?
Foster and Rahmstorf cannot say what causes this based on their analyzes alone. “The leading hypothesis, however, is based on reduced pollution of the atmosphere by cooling aerosols,” they explain. These suspended particles have long masked some of the warming by clouding the atmosphere and blocking some incoming sunlight. However, stricter environmental regulations and better air quality control have now reduced the emissions of such suspended particles from industry, power plants and traffic, especially in Asia. This eliminates the cooling effect and warming accelerates.
According to Foster and Rahmstorf, this underlines the urgency for rapid, effective climate protection: “How quickly the earth continues to warm ultimately depends on how quickly we reduce global CO2 emissions from fossil fuels to zero,” says Rahmstorf.
Source: Grant Foster, Stefan Rahmstorf (Potsdam Institute for Climate Impact Research), Geophysical Research Letters, doi: 10.1029/2025GL118804