"2023 was the hottest summer in the extratropical Northern Hemisphere in the last 2,000 years", write the authors who reconstructed past temperatures for the months of June-August, as reported in Nature by AFP.

"We shouldn't be surprised", said Jan Esper, a climatology professor at the University of Mainz in Germany and the lead author of the study, in an interview with AFP. "For me, this is just a continuation of what we started by releasing greenhouse gases", with the massive use of fossil fuels beginning in the industrial era, he emphasized.

For this study, scientists used data provided by tree rings to estimate temperatures before they were recorded by measuring instruments, that is, before the year 1850 and up to the year 1 AD.

By analyzing tree rings—the concentric rings that form in the cross-section of a tree trunk over time—it is possible to accurately reconstruct past climatic conditions using a discipline known as dendrochronology.

The study shows that the summer of 2023 was at least half a degree Celsius warmer than the summer of 246, the hottest in this pre-instrumental record period. This value considers a specific margin of uncertainty for historical data. Without this margin, the summer of 2023 would have been even 1.19°C warmer than the summer of 246.

The difference from the past increases even more when the coldest years are considered, highlighting the exceptional nature of recent warming. For example, the summer of 2023 was nearly 4°C warmer than the summer of 536, when temperatures significantly dropped due to a volcanic eruption.

Deadly heat

Hotter summers also have health consequences: in another study published on May 14 in Nature Communications, researchers determined that tens of millions of people over the age of 69 will be exposed to extremely hot days, dangerous to their health, by 2050.

Currently, 14% of elderly people are exposed to days when the thermometer exceeds 37.5°C, which can exacerbate a range of medical problems and even lead to death. According to the study, this proportion is expected to rise to 23% by 2050.

"Different countries around the world face similar problems", said Giacomo Falchetta, the lead author of the study from the Euro-Mediterranean Center for Climate Change in Venice, to AFP. "But levels of preparedness and the capacity of people and society to adapt are different", he noted.

Europe, the fastest-warming continent, will face a more brutal change, even though governments here have implemented measures to support the population during heatwaves in most countries.

Meanwhile, some parts of Africa and Asia are already accustomed to extreme temperatures, but lack the resources, such as drinking water or healthcare systems, to help the elderly.

While the mid-century may still seem far away, Giacomo Falchetta emphasizes that some of the people who will be vulnerable to heat at that time are around 40 years old today.

Although it is impossible to prevent population aging, the world can drastically reduce greenhouse gas emissions resulting from the use of oil, gas and coal by 2050. "This can reduce, to some extent, the exposure to the heat that will be felt", insists the researcher.