2023 was the Northern Hemisphere’s hottest summer in 2,000 years, new study says

(CN) — Environmental scientists say in a study published in Nature Tuesday that summer temperatures in 2023 were nearly 3.7 degrees Fahrenheit warmer than the historical average, making last summer the hottest in 2000 years.

Jan Esper and Max Torbenson of Johannes Gutenberg University and Ulf Büntgen of the University of Cambridge examined aggregated temperature data from 1850 onwards and compared recorded temperatures across the hemisphere in 2023 to prior years. They found that temperatures in the Northern Hemisphere’s extra-tropical regions (between 30 and 90 degrees north latitude) 30 degrees north latitude were the hottest on record — 3.67 degrees Fahrenheit warmer than the average recorded summer temperatures between 1850 and 1900.

“This alarming finding not only demonstrates that 2023 saw the warmest ever recorded summer across the NH extra-tropics, but also that the 2015 Paris Agreement to constrain warming globally to [2.7 degrees] has already been superseded at this limited spatial scale," the scientists said in the study.

The scientists also compared the 2023 data to nine tree-ring chronologies that estimate temperatures back more than two thousand years. They found that 2023 was 2.14 degrees warmer than the hottest summer in the tree-ring date: 246 A.D. That data also highlighted that last summer’s temperatures were well above the expected .09 degree variance.

The team also examined how the El Niño climate pattern affected last summer’s temperatures. Though above-average warming is expected in El Niño years, the heat in 2023 exceeded the previous El Niño in 2016 by 0.41 degrees

“Although 2023 is consistent with a greenhouse gases-induced warming trend that is amplified by an unfolding El Niño event, this extreme emphasizes the urgency to implement international agreements for carbon emission reduction," the scientists said in the study.

The paper stressed that this specific pattern cannot be assumed or transferred to a global scale, citing differences between tropical and extratropical climate patterns and between land temperatures and sea surface or undersea temperatures. But in the conclusion of their study, the scientists noted that their work “clearly demonstrates the unparalleled nature of present-day warmth … and reinforces calls for immediate action towards net-zero emissions."

Their emphasis on climate action comes as heat waves continue to get longer and more severe. Multiple European agencies have found the region is not prepared for climate change’s impacts on the continent. Meanwhile, most cities in the U.S. are also falling behind on their climate goals. Globally, researchers have called for more to be done as the economic cost of climate change rises year after year.