Science Daily

by Potsdam Institute for Climate Impact Research (PIK)

    Global warming has accelerated sharply over the past decade, with Earth heating up faster than at any point since modern temperature records began in 1880. A new study from the Potsdam Institute for Climate Impact Research (PIK) provides the first statistically significant evidence that the pace of global warming has increased since around 2015, even after accounting for natural factors that temporarily raise or lower global temperatures.

    Researchers found that the planet has warmed at a rate of approximately 0.35°C per decade over the past 10 years, although the exact figure varies depending on the temperature dataset used. That is nearly twice the average rate of just under 0.2°C per decade recorded between 1970 and 2015. The findings suggest that global temperatures are not simply continuing to rise. The rate at which they are increasing has also become substantially faster.

    "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, published in the scientific journal Geophysical Research Letters.

Scientists Uncover a Hidden Acceleration in Global Warming

    Detecting changes in the underlying pace of global warming is more complicated than simply comparing temperatures from one year to the next. Natural climate patterns can temporarily make the planet warmer or cooler, potentially obscuring longer trends.

    For example, El Niño can temporarily increase global temperatures by releasing heat from the tropical Pacific Ocean into the atmosphere. Volcanic eruptions can have the opposite effect when particles released into the atmosphere reflect sunlight back into space. Changes in solar activity can also influence how much energy Earth receives from the Sun.

    These natural variations create fluctuations in temperature records that can make it difficult to determine whether the underlying warming trend is accelerating.

    To address this problem, the researchers mathematically adjusted the temperature observations to account for these known influences. This allowed them to examine the longer warming trend more clearly, without the temporary fluctuations that can disguise changes in its pace.

    "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.

    The team analyzed five major global temperature datasets (NASA, NOAA, HadCRUT, Berkeley Earth, ERA5). These widely used records combine observations and, in some cases, additional atmospheric data to track how Earth's temperature has changed over time.

    The results were remarkably consistent. Regardless of which dataset or statistical method the researchers used, they found strong evidence that global warming has accelerated.

    "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.

    In statistical terms, this means the evidence for a change in the warming trend is strong enough that the researchers could distinguish it from ordinary fluctuations in the temperature record with a confidence level exceeding 98 percent.

Even After Adjustments, 2023 and 2024 Remain the Hottest Years

    One important question was whether the extraordinary global temperatures recorded in 2023 and 2024 were making the recent warming trend appear steeper than it actually was.

    Both years were exceptionally hot, partly because of natural influences such as El Niño and a period of heightened solar activity known as the solar maximum. During a solar maximum, the Sun reaches the most active phase of its approximately 11-year cycle.

    After accounting for these effects, the researchers found that the adjusted temperatures for 2023 and 2024 were somewhat lower than the original observations. Nevertheless, both years remained the warmest since instrumental temperature records began.

    The analysis also revealed that signs of accelerating warming were already emerging in 2013 or 2014 across all five temperature datasets, indicating that the finding was not simply the result of unusually high temperatures during the most recent years.

    To determine whether the warming rate had changed since the 1970s, the researchers used two different statistical techniques. The first, called quadratic trend analysis, looks for a curved pattern in temperature records that would indicate warming is speeding up rather than continuing at a constant rate.

    The second, a piecewise linear model, compares warming trends across different periods and identifies when the rate of temperature increase appears to have changed. Unlike an approach that assumes the acceleration began in a particular year, this method allows the data to determine the most likely timing of the shift.

    Both approaches supported the conclusion that global warming has accelerated significantly.

What Is Causing Global Warming to Accelerate

    Although the findings provide strong statistical evidence that global warming is speeding up, the study was not designed to determine exactly why the acceleration has occurred.

    The researchers emphasize this distinction because detecting a change in the warming rate is different from identifying the physical processes responsible for it.

    However, the observed acceleration is consistent with what current climate models can produce. These models use established physical principles to simulate how Earth's atmosphere, oceans, ice, and land respond to changes in the climate system.

    The findings therefore do not suggest that climate models are fundamentally incapable of representing the recent increase in warming. Instead, they provide additional observational evidence that the pace of climate change can vary significantly over time.

Could Earth Exceed the Paris Agreement Limit Before 2030

    The acceleration has important implications for international efforts to limit global warming.

    Under the Paris Agreement, countries agreed to pursue efforts to limit the long-term rise in global temperatures to 1.5°C above preindustrial levels. This threshold refers to sustained global warming rather than a single unusually hot year.

    If the warming rate measured over the past decade continues, researchers warn that the planet could cross that threshold on a long-term basis sooner than previously anticipated.

"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 study highlights an increasingly important concern: Earth's temperature is not only rising, but has been rising considerably faster in recent years than during the preceding decades. Whether that rapid pace continues will have major consequences for how quickly the world reaches critical climate thresholds.