Study Finds Last Year Was Hottest Summer In Northern Hemisphere In 2000 Years

“2023 was an exceptionally hot year, and this trend will continue unless we reduce greenhouse gas emissions dramatically,” said one of the study's authors.
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2023 was the hottest summer in the Northern Hemisphere in more than 2000 years, according to a new analysis of tree rings dating back to the year 1.

Scientists at the University of Cambridge and the Johannes Gutenberg University Mainz analyzed more than 10,000 tree rings to determine temperature levels dating back two millennia. They found the average temperature from June to August 2023 was 2.2 degrees Celsius warmer than the average temperature in the same period from the year 1 to 1890, even when accounting for broad climate variations.

The research was published in the journal Nature on Tuesday.

“When you look at the long sweep of history, you can see just how dramatic recent global warming is,” said professor Ulf Büntgen, from Cambridge’s Department of Geography. “2023 was an exceptionally hot year, and this trend will continue unless we reduce greenhouse gas emissions dramatically.”

The data relied on tree rings from 15 different regions across the Northern Hemisphere. Esper told The Associated Press there was not enough data to publish similar findings about heat in the Southern Hemisphere, but there were similarities in the limited tree rings they were able to examine.

A damaged saguaro cactus stands in the Sonoran Desert in Phoenix in August 2023. The iconic cactuses were under increased stress from extreme heat during Arizona’s brutal summer heat wave and are threatened by a number of issues linked to climate change.
A damaged saguaro cactus stands in the Sonoran Desert in Phoenix in August 2023. The iconic cactuses were under increased stress from extreme heat during Arizona’s brutal summer heat wave and are threatened by a number of issues linked to climate change.
Mario Tama via Getty Images

The findings only bolster those from last year after the World Meteorological Organization said the Northern Hemisphere had suffered the hottest summer ever measured. The world’s oceans were the hottest ever recorded, parts of North America suffered through a horrific wildfire season, and some cities saw stretches of punishing heat for weeks on end.

It was so hot in Phoenix that saguaro cactuses were losing arms and dying.

Overall, 2023 clocked in as the planet’s warmest year on record by a wide margin. That record heat was likely bolstered by El Niño conditions.

“It’s true that the climate is always changing, but the warming in 2023, caused by greenhouse gases, is additionally amplified by El Niño conditions, so we end up with longer and more severe heat waves and extended periods of drought,” professor Jan Esper of Johannes Gutenberg University Mainz, the lead author of the paper, said in a statement. “When you look at the big picture, it shows just how urgent it is that we reduce greenhouse gas emissions immediately.”

Thousands of sun-seekers and sunbather enjoy a late summer heat wave at Brighton seafront in the United Kingdom in September 2023.
Thousands of sun-seekers and sunbather enjoy a late summer heat wave at Brighton seafront in the United Kingdom in September 2023.
Anadolu via Getty Images

Scientists have warned with increasing urgency that the planet remains firmly in the grips of a climate emergency due to nations’ reliance on greenhouse gas-producing fossil fuels.

In a speech last September, António Guterres, the secretary-general of the United Nations, said humanity had “opened the gates to hell” and said while strides had been made in the transition to renewable energy, the planet was still “decades behind.”

“We must make up time lost to foot-dragging, arm-twisting and the naked greed of entrenched interests raking in billions from fossil fuels,” he said at the time. “Shady pledges have betrayed the public trust. ... Shamefully, some companies have even tried to block the transition to net zero ― using wealth and influence to delay, distract and deceive.”

The National Weather Service has already issued warnings about the upcoming summer, saying it could be rife with hotter-than-normal, and possibly record-breaking, conditions once more.

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