2023 Was the Hottest Summer in More Than 2,000 Years in the Northern Hemisphere, According To Tree Rings

By: Julia | Published: May 15, 2024

By analyzing tree rings, scientists have discovered that 2023 was the hottest summer in the Northern Hemisphere in more than 2,000 years.

This remarkable discovery comes as many researchers have stated that climate change is increasing the Earth’s temperature at an increasingly worrying rate.

2023’s Record-Breaking Summer

During the very hot days of the summer of 2023, many researchers and weather organizations declared that it was likely the hottest summer on record.

A meadow and green trees seen in the sunlight.

Source: Dakota Roos/Unsplash

However, many of these records tend to only go back to 1850, at the very most. This left many researchers wondering if 2023’s incredibly hot summer was unique — or if past summers hundreds of years ago were hotter.

Analyzing Tree Rings

A team of scientists got together and analyzed more than 10,000 tree rings in the Northern Hemisphere to see just where 2023’s summer stood up to other summers long ago.

A close-up look at an old tree’s rings.

Source: Joey Kyber/Unsplash

According to this new study published in the journal Nature, 2023 had the hottest summer, and the highest temperatures, ever seen in at least the last 2,000 years.

Looking at Past Temperatures

Researchers were able to look at many tree rings to see if any other year had as hot a temperature as was seen in the Northern Hemisphere in 2023.

Many people eating food outside a street vendor during the summer in New York.

Source: Emily Fletke/Unsplash

Though scientists were able to trace back temperatures to year 1, thanks to these tree rings, they did not find a year that had a temperature that came anywhere close to the heat seen in the summer of 2023.

The Hottest Year Seen Before 2023

According to these tree rings and the well-established method that these researchers used, the year 246 was the hottest year before humans began to put gases into the Earth’s atmosphere, thanks to the use of natural gas, oil, and coal.

Many people seen on the beach under umbrellas in the daytime.

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However, 2023 was much hotter than what was seen in 246. Researchers have stated that 2023 was about 2.1 degrees Fahrenheit warmer than 246’s summer.

Past Hot Years

The summer of 2023 isn’t alone in beating out the temperature seen in year 246, though. The study’s co-author Max Torbenson has claimed that many of our past summers in the last few decades have been hotter than 246’s summer.

A small tree with barely any branches underneath a harsh sunlight in the daytime.

Source: Elimende Inagella/Unsplash

However, 2023 still comes in as the hottest summer ever recorded — and the hottest summer these trees have seen in 2,000 years.


The Trees Used in This Study

To completely understand the data they were collecting, the team analyzed 10,000 trees in about 15 different locations, all of which were in the Northern Hemisphere and were north of the tropics.

The sunlight shining through tree branches in the daytime.

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Though the team did collect data from the Southern Hemisphere, they couldn’t find enough to publish it alongside their Northern Hemisphere collections. However, the data from the Southern Hemisphere did match what they found in the north.


What Other Scientists Are Saying

Other scientists who weren’t a part of this study have come out to analyze the data gained from these tree rings. Michael Mann, a climate scientist at the University of Pennsylvania, has stated that they could use other forms of data to go back even further when looking at temperatures.

A close-up of a brown tree stump and its rings.

Source: Simon Stankowski/Unsplash

For example, Mann has stated that corals and ice cores are much more reliable than tree rings.


Going Back 20,000 Years

Mann is possibly best known for publishing the hockey stick graph, which shows how temperatures have risen on Earth since the Industrial Age.

An orange sun seen behind palm trees during sunset.

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According to Mann, using other forms of data could allow scientists to find out if 2023’s temperatures are the hottest seen in the past 20,000 years.


Why the Team Used Tree Rings

The study’s lead author Jan Esper has explained that his team used tree rings because this data is precise. They can analyze these tree rings and find out each summer’s temperature, for each year.

A close-up of many trees and their tree rings.

Source: Monika Grabkowska/Unsplash

Esper has further stated that this precise summer data cannot be done by using other forms of proxies, such as ice cores or corals.


Going Back 120,000 Years

Zeke Hausfather, a Berkeley Earth climate scientist, also wasn’t a part of the study. However, after looking at it, he has stated that 2023’s summer may have been the hottest summer ever seen in the last 120,000 years.

A close-up view of a brown tree trunk and its rings.

Source: Volodymyr Hryshchenko/Unsplash

However, Hausfather has explained that very precise data doesn’t go back this far.


Climate Change Worries

This study has only further increased the worries that many climate scientists have about ongoing climate change and global warming issues. This data has proven that our summers are much hotter than what has ever been seen before.

An orange sky seen as the sun sets over the ocean.

Source: Thomas Bormans/Unsplash

Esper has also stated that the last 150 years have seen temperatures generally increase slowly, before a huge giant leap in temperatures is seen.