Over the past decade, global temperatures have risen at an estimated pace of about 0.35°C per decade, depending on the dataset used. By comparison, the average warming rate from 1970 to 2015 was just under 0.2°C per decade. The recent pace is higher than that of any previous decade since instrumental temperature records began in 1880.

Scientists Isolate the Long-Term Warming Signal

"We can now demonstrate a strong and statistically significant acceleration of global warming since around 2015," says Grant Foster, a US statistics expert and co-author of the study, which was published today in the scientific journal Geophysical Research Letters.

"We filter out known natural influences in the observational data, so that the 'noise' is reduced, making the underlying long-term warming signal more clearly visible," Foster added.

In climate data, "noise" refers to short-erm temperature changes that can temporarily hide or exaggerate the underlying trend. El Niño, for example, can push global temperatures higher for a limited period by releasing heat from the tropical Pacific Ocean into the atmosphere. Volcanic eruptions can have the opposite effect by sending particles into the atmosphere that reflect sunlight, while changes in the Sun's activity can also produce smaller temperature variations.

To separate these temporary influences from the broader warming trend, the researchers analyzed measurements from five widely used global temperature data sets (NASA, NOAA, HadCRUT, Berkeley Earth, ERA5).

"The adjusted data show an acceleration of global warming since 2015 with a statistical certainty of over 98 percent, consistent across all data sets examined and independent of the analysis method chosen," explains Stefan Rahmstorf, PIK researcher and lead author of the study.

Warming Acceleration Appears Across Five Datasets

A statistical certainty of more than 98 percent means the researchers found strong evidence that the change in the warming rate is real rather than the result of random variation in the data. The same overall pattern appeared in all five temperature records, even though the datasets are produced by different scientific organizations and use somewhat different methods.

After the researchers adjusted for El Niño and the solar maximum, the extreme warmth of 2023 and 2024 was reduced slightly in the analysis. Even so, both years remained the two warmest since instrumental records began.

Across all of the datasets, the acceleration started to become visible in 2013 or 2014. The researchers describe the broader shift as beginning around 2015, when the evidence became clearer.

Two Statistical Methods Point to the Same Shift

To determine whether the warming rate had changed since the 1970s, the team used two statistical approaches. The first was a quadratic trend analysis, which tests whether the temperature curve is bending upward over time rather than rising at a constant rate.

The second was a piecewise linear model. This method divides the temperature record into separate periods and objectively identifies when the rate of warming appears to change. Both approaches supported the conclusion that global warming has accelerated.

Study Does Not Identify the Cause

The research was designed to detect and measure the statistical acceleration, not to determine exactly why it has occurred.

However, the authors noted that climate models can produce periods in which warming speeds up. In other words, an increasing rate of warming is consistent with the range of behavior represented in current climate modeling.

Climate models are computer simulations that use the laws of physics to estimate how the atmosphere, oceans, ice, and land respond to greenhouse gases and other influences. They do not predict every short-term fluctuation perfectly, but they help scientists evaluate long-term climate patterns and possible future changes.

1.5°C Threshold Could Be Exceeded Before 2030

"If the warming rate of the past 10 years continues, it would lead to a long-term exceedance of the 1.5°C limit of the Paris Agreement before 2030," says Stefan Rahmstorf. "How quickly the Earth continues to warm ultimately depends on how rapidly we reduce global CO2 emissions from fossil fuels to zero."

The 1.5°C limit refers to the goal of restricting long-term global warming to 1.5°C above preindustrial temperatures. A single year above that level does not by itself mean the Paris Agreement threshold has been permanently crossed. Scientists generally focus on sustained warming over a longer period.

The findings suggest that Earth may now be warming considerably faster than it did during the final decades of the 20th century. Whether that acceleration continues will depend heavily on future carbon dioxide emissions from coal, oil, and natural gas.