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While parts of the world have warmed or cooled in the past, modern climate change is happening just about everywhere at the same time.
From the planet’s perspective, one of the most significant events of the past 2,000 years occurred on April 5, 1815, when the Indonesian volcano Mount Tambora began to erupt. “The noise was, in the first instance, almost universally attributed to a distant cannon,” wrote a British statesman stationed hundreds of miles away on Java. Soon “the sun became obscured” with ash, and by the next week, fog-like smoke reduced visibility to 900 feet, while earthquakes shook the island.
Tambora was the largest volcanic eruption since the end of the last Ice Age, one of a series of eruptions that pumped huge amounts of sunlight-reflecting gas into the atmosphere. This gas darkened and chilled summers in Europe. It weakened the monsoons in India and West Africa. It allowed glaciers to advance in the Alps.
In other words, these eruptions brought about a kind of natural climate change. But it was felt differently in different places. And new research confirms that it pales in comparison to the climate change we now face.
Drawing on a huge database of climate-recording objects from all over the world—including tree rings, cave formations, and ancient pollen trapped in lake mud—the study concludes that 98 percent of Earth’s surface experienced its hottest period of the past 2,000 years within living memory. That uniform heat spike “is unprecedented over the Common Era,” it says.
This latest finding may not surprise most climate scientists, who suspect that the planet is as hot now as it’s ever been in at least the past 125,000 years. But it may shock some politicians, who have downplayed modern-day climate change by talking about those past shifts. “The climate has always been changing. There has never been a time when the climate has not changed,” said Senator Marco Rubio at a Republican presidential debate in 2016.
To which the study replies: Sure. It just hasn’t changed like this.
In fairness, that wasn’t always clear. Decades ago, researchers talked about the past periods of climate change as global events. They cited the Little Ice Age, which began in roughly 1550 and ended around 1850, as an era when global temperatures fell everywhere. But this study—and work from other scholars—suggests that the Little Ice Age wasn’t global at all, and mostly lowered temperatures in western Europe and parts of North America.
“Traditionally, the understanding of climate over [the past 2,000 years] is that there were globally coherent periods of climate variability—that there was a cold period called the Little Ice Age, [or] that there was a warm period called the Medieval Climate Anomaly,” said Nathan Steiger, an author of the paper and a research scientist at Columbia, at a press conference this week. “What we show is that these periods weren’t globally coherent, as previously thought.”
What makes those older eras different from modern warming is coherence—that climate change is happening today just about everywhere at the same time. “That coherence cannot be explained by the natural variability of the climate system,” Steiger said. And it does not characterize any previous era.
“This study is another nail in the coffin of the idea of that there was a globally warm or cold period that fit tidily into a specific couple of centuries,” said Yarrow Axford, a climate scientist at Northwestern University, in an email. She was not involved in writing the new paper. The idea that the Little Ice Age or eras like it were uniform global events was “already dying within the scientific community,” she said, yet that idea remains “perennially popular with nonexperts who want to sow doubt about the significance of the dramatic and truly global warming that has occurred in the past century.”
Among the nonexperts who have tacitly embraced that idea: Donald Trump. The president has repeatedly brought up the fluctuating nature of the climate in order to downplay current change. “Something’s changing, and it’ll change back again,” he said on 60 Minutes last year.
Robinson Meyer is a staff writer at The Atlantic, where he covers climate change and technology.