Home Business Summer 2023 was the hottest in the Northern Hemisphere in 2,000 years, study says

Summer 2023 was the hottest in the Northern Hemisphere in 2,000 years, study says

by SuperiorInvest

The summer of 2023 was exceptionally hot. Scientists have already established that it was the warmest summer in the Northern Hemisphere since around 1850, when people began systematically measuring and recording temperatures.

Now, researchers say it was the hottest in 2,000 years, according to a new study published in the journal Nature that compares 2023 to a longest temperature record in most of the Northern Hemisphere. The study dates back to before the advent of thermometers and weather stations, to 1 AD, using evidence from tree rings.

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

Additional greenhouse gases in the atmosphere from burning fossil fuels are responsible for most of Earth's recent temperature increases, but other factors (including El Niño, an undersea volcanic eruption, and a reduction in pollution from sulfur dioxide aerosols from container ships) may have contributed to last year's extreme heat.

The average temperature from June to August 2023 was 2.20 degrees Celsius warmer than the average summer temperature between the years 1 and 1890, according to the researchers' tree ring data.

And last summer was 2.07 degrees Celsius warmer than the average summer temperature between 1850 and 1900, the years typically considered the baseline for the period before human-caused climate change.

The new study suggests that Earth's natural temperature was colder than this baseline, which is frequently used by scientists and policymakers when discussing climate goals, such as limiting global warming to 1.5 degrees Celsius above the preindustrial era.

“This period is really not well covered with instruments,” Dr. Esper said, adding that “tree rings can work very, very well. So we can use this as a substitute and even as a corrective.”

The trees grow each year in a different pattern of light-colored rings in spring and early summer, and darker rings in late summer and fall. Each pair of rings represents a year, and the differences between the rings offer scientists clues about changing environmental conditions. For example, trees tend to grow larger and form wider rings during warm, wet years.

This study compared temperatures in 2023 with a previously published reconstruction of temperatures over the past 2,000 years. More than a dozen research groups collaborated to create this reconstruction, using data from about 10,000 trees in nine regions of the Northern Hemisphere between 30 and 90 degrees latitude, or everywhere above the tropics. Some data came from drilling very thin cores from live trees, but most came from dead trees and historical wood samples.

Covering longer time periods results in more volcanic eruptions being included in the data. Large eruptions, at least on land, can cool the Earth by spraying sulfur dioxide aerosols into the atmosphere. In the last 2,000 years, there have been between 20 and 30 such eruptions that reduced average temperatures, Dr. Esper said.

(The recent Hunga Tonga eruption, by contrast, occurred under the ocean and spewed enormous amounts of water vapor into the atmosphere. Water vapor is a powerful greenhouse gas.)

Not everyone agrees that tree rings offer a more accurate picture of past temperatures than historical records.

“It remains an area of ​​active research,” said Robert Rohde, senior scientist at Berkeley Earth. Dr. Rohde was not directly involved in the new study, but data from his organization were used. “This is not the first paper to suggest that there is a warm bias in the early instrumental period, by no means. But I don't think it's really resolved.”

To some extent, the slight differences between the stories that thermometers and tree rings tell us about Earth's past don't matter in the present, said Zeke Hausfather, another Earth scientist at Berkeley.

“It's an academic question rather than a practical one,” he said. “Reassessing temperatures in the distant past doesn't really tell us much about the effects of current climate change.”

Last year, those effects included a heat dome that settled over much of Mexico and the southern United States for weeks. Japan had the hottest summer ever recorded. Canada suffered its worst wildfire season in history and parts of Europe also battled a series of destructive wildfires. 2024 is expected to be another hot year.

Source Link

Related Posts