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Study finds summer 2023 will be the hottest in the Northern Hemisphere in 2000

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The summer of 2023 will be extremely hot.Scientists have determined that it is The warmest summer in the Northern Hemisphere Since around 1850, people have been systematically measuring and recording temperature.

Now it’s the hottest weather since 2000, according to researchers A new study published in the journal Nature Compared to 2023, much of the Northern Hemisphere is experiencing longer temperature records. The study used evidence of tree rings dating back to before the advent of thermometers and weather stations in 1 AD.

“This gives us a comprehensive picture of natural climate variability,” said the paper’s lead author Jan Esper, a climatologist at Johannes Gutenberg University in Mainz, Germany.

Additional greenhouse gases in the atmosphere from the burning of fossil fuels are the main cause of recent increases in Earth’s temperature, but other factors include El NiñoUndersea volcanic eruptions and a reduction in sulfur dioxide aerosol pollution from container ships may have contributed to last year’s extreme heat.

According to the researchers’ tree-ring data, the average temperature from June to August 2023 was 2.20 degrees Celsius higher than the average summer temperature from 1 to 1890.

Last summer was 2.07 degrees Celsius warmer than the average summer temperature between 1850 and 1900, the years generally considered the baseline for the period before man-made climate change.

The new study shows that Earth’s natural temperatures are below this baseline, which is often used by scientists and policymakers when discussing climate goals, such as limiting global warming to 1.5 degrees Celsius above pre-industrial times.

“This period is really not well covered with instruments,” Dr. Esper said, adding, “Tree rings can be done very, very well. So we can use that as a proxy or even as a correction.”

Trees have a unique way of growing wider each year, showing light rings in spring and early summer and dark rings in late summer and fall. Each pair of rings represents a year, and the differences between the rings give scientists clues about changing environmental conditions. For example, during warm, wet years, trees tend to grow more and develop wider growth rings.

This study compares temperatures in 2023 with Previously published temperature reconstructions for the past 2,000 years. More than a dozen research groups collaborated to create the reconstruction, using data from about 10,000 trees in nine regions in the Northern Hemisphere between 30 and 90 degrees latitude, or anywhere above the tropics. Some of the data comes from drilling very thin cores from living trees, but most of the data comes from dead trees and historical wood samples.

Covering a longer time period results in more volcanic eruptions being included in the data. Large eruptions, at least on land, can cool the planet by spewing sulfur dioxide aerosols into the atmosphere. Dr. Esper said there have been about 20 to 30 such eruptions over the past 2,000 years, causing average temperatures to drop.

(recent Honga Tonga In contrast, volcanic eruptions occur under the sea and spew large amounts of water vapor into the atmosphere. Water vapor is a powerful greenhouse gas. )

Not everyone agrees that tree rings describe past temperatures more accurately than historical records.

“This is still an active area of ​​research,” said Robert Lord, chief scientist at the Berkeley Earth Institute. Dr. Lord was not directly involved in the new study, but data from his organization was used. “This is not the first paper by any means to suggest a warmth bias in the early instrumental period. But I don’t think the matter has really been settled yet.”

Zeke Hausfather, another Berkeley geoscientist, said that in some ways, the subtle differences between what thermometers and tree rings tell us about the Earth’s past are not important in the present.

“This is an academic question, not a practical question,” he said. “Reassessing temperatures in the distant past doesn’t tell us much about the effects of climate change today.”

Last year, those effects included a heat dome that enveloped much of Mexico and the southern United States for weeks. Japan experienced its hottest summer on record. Canada is experiencing its worst wildfire season on record, and parts of Europe have been hit by a series of devastating wildfires. 2024 is Another hot year is expected.

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