It's Official: Summer 2023 Was The North's Hottest in 2,000 Years

Tree ring data confirms it's been 2,000 years since the Northern Hemisphere had a summer as hot as last year's. Not since the height of the Roman Empire has life on Earth experienced a summer so extreme.

The new analysis suggests we've breached the 2015 Paris Agreement to limit warming to 1.5 °C above pre-industrial levels, at least temporarily in the north.

Many people are already dying as a direct consequence of all this excess heat, as well as from the many natural disasters it's fueling.

"When you look at the long sweep of history, you can see just how dramatic recent global warming is," says University of Cambridge environmental scientist Ulf Büntgen, who co-authored the new study.

He continues: "2023 was an exceptionally hot year, and this trend will continue unless we reduce greenhouse gas emissions dramatically."

Büntgen, along with his colleagues, climatologists Jan Esper and Max Torbenson, from Johannes Gutenberg University in Germany, compiled early temperature records with indirect measures from large-scale tree ring datasets from across the Northern Hemisphere.

Cross section of a tree trunk revealing annual rings. (MirageC/Getty Images)

Using temperature proxies like these are necessary because early temperature measurements were sparse and not taken systematically.

"Only when we look at climate reconstructions can we better account for natural variability and put recent anthropogenic climate change into context," explains Büntgen.

Their results suggest the pre-industrial baseline from which we measure changes in global temperatures was ever so slightly colder than we thought.

But when it comes to the impacts of climate change, every fraction of a degree matters. Recalibrating this baseline means the 2023 Northern Hemisphere summer was 2.07 °C warmer than the mean temperatures of the preindustrial period between 1850 to 1900.

Instrumental summer land temperatures (red) with the tree ring reconstruction mean (yellow). (Esper et al., Nature, 2024)

While their results are only limited to the Northern Hemisphere, upwards of 30°N, another study from earlier this year came to a similar conclusion using sea sponge skeletons to find the pre-industrial baseline temperature. (That study, however, has been criticized by scientists who point out the sea sponges represent only a single record from one place, the Caribbean.)

Another recent analysis, published in February by the European Union's climate service, indicated that global warming breached 1.5 °C for the entire year last year, but scientists stress we can still turn the situation around if we act fast.

"It's true that the climate is always changing, but the warming in 2023, caused by greenhouse gases, is additionally amplified by El Niño conditions, so we end up with longer and more severe heat waves and extended periods of drought," explains Esper.

"When you look at the big picture, it shows just how urgent it is that we reduce greenhouse gas emissions immediately."

Meanwhile, fossil fuel companies and other powerful industries just keep adding more heat-trapping CO2 into our air, with impunity, while scientists and now the planet itself keep warning of the consequences.

"We keep [working] because we have to do it, so [the powerful] cannot say that they didn't know," climate scientist Ruth Cerezo-Mota, who was not involved in the new study, recently told The Guardian.

"We know what we're talking about. They can say they don't care, but they can't say they didn't know."

This research was published in Nature.