The scorching summer of 2023 was the hottest in the Northern Hemisphere in more than 2,000 years, a new study finds.
When temperatures soared last year, several weather agencies said it was the hottest month, summer and year on record. But these records only go back to 1850 at best because they are based on thermometers. Now scientists can go back to Year 1 of the modern Western calendar, when the Bible says Jesus Christ walked the Earth, but they have found no northern summer hotter than last year.
A study published Tuesday in the journal Nature uses a well-established method and record of more than 10,000 tree rings to calculate summer temperatures for every year since Year 1. No year has come even close to the intense heat of last summer, it said. lead author Jan Esper, a climate geographer at Gutenberg Research College in Germany.
Before humans began pumping heat-trapping gases into the atmosphere by burning coal, oil and natural gas, the hottest year was the year 246, Esper said. This was the beginning of the medieval period of history, when the Roman Emperor Philip the Arab fought the Germans along the Danube River.
Esper’s paper showed that in the Northern Hemisphere, the summer of 2023 was up to 2.1 degrees Fahrenheit (1.2 degrees Celsius) hotter than the summer of 246. In fact, 25 of the last 28 years have been hotter than that. medieval summer, he said. study co-author Max Torbenson.
“That gives us a good idea of how extreme 2023 is,” Esper told the Associated Press.
The team used thousands of trees in 15 different locations in the Northern Hemisphere, north of the tropics, where there was enough data to get a good number from year 1, Esper said. There wasn’t enough data on trees in the Southern Hemisphere to publish, but the sparse data showed something similar, he said.
Scientists look at trees’ annual growth rings and “we can match them almost like a puzzle in time, so we can assign annual dates to each ring,” Torbenson said.
Why stop looking at year 1 when other temperature reconstructions go back more than 20,000 years, asked University of Pennsylvania climate scientist Michael Mann, who was not part of the study but more than a quarter century ago published it. the famous hockey stick graph showing rising temperatures since the Industrial Age. He said relying on tree rings alone is “considerably less reliable” than looking at all kinds of proxy data, including ice cores, corals and more.
Esper said his new study uses only tree data because it is accurate enough to provide summer-to-summer temperature estimates, which cannot be done with corals, ice cores and other indicators. Tree rings have higher resolution, he said.
“The global temperature records set last summer were so impressive – breaking the previous record by 0.5°C in September and 0.4°C in October – that it is not surprising that they are clearly the hottest in the last 2,000 years,” said the scientist. climate of Berkeley Earth. Zeke Hausfather, who was not part of the study. “It’s probably the hottest summer in the last 120,000 years, although we can’t be completely sure,” he said, because the precise data for one year isn’t that old.
Because the annual high-resolution data doesn’t go back that far, Esper said it’s wrong for scientists and the media to call it the hottest in 120,000 years. Two thousand years are enough, he said.
Esper also said that the pre-industrial period from 1850 to 1900 that scientists – especially the Intergovernmental Panel on Climate Change – use as a base period before warming may be slightly cooler than instrumental records show. Instruments from that time were more often exposed to the hot sun rather than protected as they are now, and tree rings continue to show that it was about 0.4 degrees (0.2 degrees Celsius) colder than thermometers show.
This means there has been a little more warming due to human-caused climate change than most scientists calculate, an issue that has been discussed by researchers in recent years.
Looking at temperature records, especially from the last 150 years, Esper noticed that although they are generally increasing, they tend to do so in slow climbs and then in giant strides, like what happened last year. He said these steps are often associated with a natural El Nino, a warming of the central Pacific that changes the climate around the world and adds even more heat to a changing climate.
“I don’t know when the next step will be taken, but I won’t be surprised by another big step in the next 10 to 15 years, that’s for sure,” Esper said at a news conference. “And it’s very worrying.”
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