Global warming has accelerated to 0.35°C per decade, study finds

How did researchers separate acceleration from climate “noise”?

Natural climate patterns can make a long-term warming trend harder to see by temporarily pushing temperatures up or down. El Niño can release heat from the tropical Pacific Ocean into the atmosphere.

Volcanic eruptions can cool Earth when airborne particles reflect sunlight back into space, while changes in solar activity can alter how much energy Earth receives from the Sun.

The team mathematically adjusted the temperature observations for these known influences, reducing the “noise” and making the underlying long-term signal clearer. Foster described the process as filtering temporary natural effects from observational data.

Signs of acceleration were already emerging in 2013 or 2014 across all five datasets. That timing indicates the result did not arise only because the latest years were exceptionally hot.

Researchers used two techniques to test the change. Quadratic trend analysis looks for a curved temperature pattern showing warming that speeds up. A piecewise linear model compares separate periods and lets the data determine when the warming rate changed, rather than assuming a particular start date.

Both approaches supported significant acceleration.

Takeaway: The finding persists after researchers discount known natural influences and test it with two different statistical methods.

Are 2023 and 2024 distorting the result?

Researchers checked whether the extraordinary heat of 2023 and 2024 was making the recent slope look artificially steep. Both years were exceptionally hot, partly because of El Niño and a period of heightened solar activity called the solar maximum, the most active phase of the Sun’s roughly 11-year cycle.

After the researchers accounted for those influences, the adjusted temperatures for both years were somewhat lower than the original observations. Even so, 2023 and 2024 remained the warmest years since instrumental temperature records began.

The earlier appearance of acceleration in 2013 or 2014 across every dataset supports the result independently of those two recent high-temperature years.

Takeaway: Adjusting the hottest years lowers their temperatures slightly but does not erase either their records or the detected speedup.

What is causing the acceleration?

The study was designed to detect whether the warming rate had changed, not to determine which physical processes produced that change. Detecting a statistical shift and identifying its cause are separate steps.

The observed acceleration is nevertheless consistent with what current climate models can produce. Those models use established physical principles to simulate how the atmosphere, oceans, ice and land respond to changes in the climate system.

The findings therefore do not indicate that climate models are fundamentally unable to represent the recent increase in warming. Instead, they add observational evidence that the pace of climate change can vary significantly over time.

Takeaway: The data show a robust statistical speedup, but they do not assign that speedup to a specific mechanism.

Could Earth exceed the Paris Agreement limit before 2030?

Under the Paris Agreement, countries agreed to pursue efforts to limit long-term global warming to 1.5°C above preindustrial levels. The threshold concerns sustained warming, not a single unusually hot year.

“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,” Rahmstorf said. “How quickly the Earth continues to warm ultimately depends on how rapidly we reduce global CO2 emissions from fossil fuels to zero.”

That projection depends on the recent rate continuing. Rahmstorf tied the future pace to how quickly countries reduce carbon dioxide emissions from fossil fuels to zero.

Takeaway: Faster warming could bring the sustained 1.5°C threshold forward, but future emissions will determine whether the recent pace lasts.