Research from climate scientist Michael Mann, Presidential Distinguished Professor of Earth & Environmental Science, and colleagues vindicates climate models and reframes the record heat of 2024.
2 min. read
In 2023 and 2024, global temperatures reached a new high. The World Meteorological Organization declared 2024 the hottest year on record as extreme heatwaves, devastating floods, and ferocious wildfires continued to sweep across the globe. The surge prompted some scientists and journalists to suggest that the planet’s warming was not explicable.
Climate scientist Michael Mann and colleagues argue that the record warmth seen two years ago is entirely consistent with expectations on a warming planet.
(Image: Courtesy of Penn Arts & Sciences)
But Michael Mann, Presidential Distinguished Professor of Earth & Environmental Science in the School of Arts & Sciences, wasn’t convinced. “That framing is unfortunate,” he says. “It makes it sound like we don’t understand what’s driving climate change.”
So Mann and colleagues set out to test whether the surge in temperatures really defied explanation. A new study published in Proceedings of the National Academy of Sciences argues that the record warmth was entirely consistent with expectations on a warming planet: When accounting for human-caused warming alongside natural climate variability like El Niño and La Niña climate patterns, the 2024 temperatures actually showed that climate models today are capturing the ongoing warming of the planet well.
To untangle how much of the 2024 heat came from human-caused warming versus the natural push and pull of El Niño and La Niña—the recurring Pacific climate cycle that temporarily spikes or suppresses global temperatures—Mann’s team used a modeling technique that combined real-world temperature observations with climate model results to generate 40,000 synthetic climate simulations, essentially creating tens of thousands of alternative versions of climate history. Mann calls this a sort of “climate multiverse,” where human-caused warming remains constant across all simulations, but unpredictable events like El Niño and La Niña get randomized.
The simulations showed that 2024’s record-setting heat was far from an anomaly. When accounting for human-caused warming, the researchers estimated it had roughly a 12 percent probability of occurring—in other words, it could be expected to occur on average once in eight years. Strip out the baseline of human-caused warming from the models entirely, and the picture changes; in all 40,000 simulations without this signal, temperatures as high as those seen in 2024 didn’t even appear once.
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