(NEW YORK) — A closer look at tree rings is adding to the growing list of evidence that shows unprecedented temperatures measured on Earth over the past year.

The summer of 2023 was the warmest in the Northern Hemisphere extra-tropical regions — from about New Orleans to the North Pole — in the past 2,000 years, according to a study published in Nature on Tuesday.

Land temperatures in this section of the Northern Hemisphere were 2.07 degrees Celsius — or about 3.73 degrees Fahrenheit — higher in the summer of 2023 than instrumental averages between 1850 and 1900, researchers discovered after combining measurements from thousands of meteorological stations to analyze the June-through-August surface air temperatures across the Northern Hemisphere’s extra-tropical region, which include 30 to 90 degrees north, according to the study.

The researchers also spent months taking samples to compare tree ring reconstruction with nine of the longest temperature-sensitive tree chronologies available for the results, Jan Esper, a professor for climatology at Johannes Gutenberg University in Mainz, Germany, and lead author of the study, told reporters during a press briefing on Monday.

Tree rings are “the only proxy” that can provide annual temperature reconstructions, especially since early instrumental temperatures tend to have a “warm bias,” Esper said.

These observations give scientists “the full picture” of natural climate variability, Esper said.

While the data shows enough of a chance for extreme summers prior to Industrialization, almost every one of the “cold years” can be attributed to volcanic eruptions, Esper said.

The sample regions offer a “fairly good spatial representation” in terms of longitude but has some limitations for latitude, Max Torbenson, research associate at Johannes Gutenberg University’s department of geography and co-author of the paper, said during Monday’s press briefing.

While the warming investigated in the paper cannot be applied on a global scale, it demonstrates “the unparalleled nature of present-day warming” as well as the need for urgent action to mitigate greenhouse gas emissions, the authors said.

Several reports have pointed to 2023 as being the warmest year on record. Copernicus, Europe’s climate change service, has named every month in 2024 so far as the warmest in recorded history.

The planet clocked an 11-month streak of record-breaking global temperatures after Copernicus named last month the warmest April ever recorded.

The results of the most recent paper are “very, very concerning,” Esper said.

“The longer we wait, the more expensive it will be and the more difficult it will be to mitigate,” Esper said of climate change.

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