Earth has been steadily warming since the start of the Industrial Revolution, when humans began emitting greenhouse gases at scale. And while the rate of warming has been largely constant for the past half-century, a recent study finds it has accelerated over the last decade — an alarming trend for Earth systems, biodiversity and human health.
Since the 1970s, the average global temperature has increased by roughly 0.2° Celsius (0.36° Fahrenheit) per decade. “That was pretty constant, but in recent years there have been some really record-breaking hot years globally,” study co-author Stefan Rahmstorf, a professor of physics of the ocean at Potsdam University in Germany, told Mongabay in a video call.
The last three years are the three warmest on record – as are all ten of the years since 2015. That sudden spike prompted a debate among climate scientists, Rahmstorf said. They questioned if the sudden warming was indeed an acceleration, or natural variation that could be explained by three other factors — El Niño, volcanic eruptions, or solar flares — which can all affect global temperatures.
To find out, Rahmstorf and study co-author Grant Foster, a statistician, applied statistical analysis to global temperature data to weed out the influence of those three factors.
“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 said in a press release.
What remained was predominantly the human-caused warming signal. The results were dramatic: since 2015, the warming rate has nearly doubled to between 0.35 and 0.4°C (0.63 and 0.72°F) per decade.
This study didn’t investigate why warming has accelerated, but Rahmstorf said the likeliest explanation is stricter regulations on shipping emissions.
Ocean-going vessels emit pollutants that contribute to more than 260,000 premature deaths annually. However, those same emissions also help form clouds over the oceans, which reflect sunlight back out to space, providing a modest cooling effect. The new shipping regulations, in force since 2020, dramatically improved air quality, saving lives, but likely also contributed to the spike in warming observed in the study.
If this hypothesis holds, Rahmstorf said, that spike is likely temporary. “This high warming rate may not continue in the next decade, because no similar big reduction in aerosols would be expected there,” he said.
If the current pace were to continue, by the end of the century Earth would be looking at roughly 4°C (7.2°F) of additional warming, which has been projected by some climate models. That much additional heat would be catastrophic for life as we know it, with dramatic sea level rise, ocean acidification, more extreme weather events, mass extinctions, and myriad human health consequences.
Rahmstorf said the amount of long-term warming will still be determined by human activity. “How quickly the Earth continues to warm ultimately depends on how rapidly we reduce global CO₂ emissions from fossil fuels to zero.”
Banner image: Glacial melt water flowing through snow in Himalayas. Photo courtesy of Sharada Prasad via Wikimedia (CC BY 2.0)
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