The year 2023, the hottest ever recorded in the world, has once again broken a new record: scientists have been able to establish that the summer in the northern hemisphere was the hottest in 2000 years, according to a study published Tuesday.
“2023 represented the hottest summer in the extra-tropical northern hemisphere over the last 2000 years,” write Tuesday in the journal Nature the authors, who reconstructed past temperatures for the months of June to August.
“We shouldn’t be surprised,” Jan Esper, professor of climatology at Gutenberg University in Mainz, Germany, and lead author of the study, told AFP. “For me, it is only the continuation of what we started by releasing greenhouse gases”, with the massive use of fossil fuels since the industrial era, he underlines.
For this study, scientists used data from tree rings to estimate temperatures before they were recorded by measuring instruments, before 1850 and up to 1 CE.
The analysis of growth rings — the concentric rings that take shape over time at the heart of the tree — makes it possible to precisely reconstruct ancient climatic conditions, according to a discipline called dendrochronology.
It appears that the summer period of 2023 was at least half a degree Celsius warmer than the summer of 246, the hottest of this period before instrumental records.
This figure takes into account a certain margin of uncertainty for past data. Without it, the summer of 2023 would be even 1.19°C hotter than that of 246.
The gap with the past widens even more if we consider the coldest years, highlighting the exceptional aspect of recent warming. Thus, the summer of 2023 was almost 4°C warmer than the summer of 536, when temperatures plunged due to a volcanic eruption.
Deadly heat
Hotter summers also have health consequences: in another study published Tuesday in the journal Nature Communicationsresearchers have established that tens of millions of people over the age of 69 will be exposed to days of extreme heat dangerous to their health by 2050.
Today, 14% of seniors are exposed to days when thermometers rise above 37.5°C, which can aggravate a number of medical problems and even lead to death. This figure is expected to rise to 23% in 2050, according to the study.
“Different countries around the world are facing similar problems,” commented to AFP Giacomo Falchetta, from the Euro-Mediterranean Center on Climate Change in Venice, the lead author. “But the levels of preparation, the adaptability of people and society are different,” he notes.
Europe, the continent that is warming the fastest, will thus be faced with a more brutal change, even if governments have put in place measures to support populations during heatwaves in most countries.
Certain regions of Africa and Asia are already accustomed to extreme temperatures but, on the contrary, lack the resources – drinking water or health system – to help the elderly.
Although the middle of the century may still seem far away, Giacomo Falchetta points out that some of the people who will then be vulnerable to the heat are in their forties today.
While it is impossible to prevent population aging, the world can drastically reduce greenhouse gas emissions from the use of oil, gas and coal by 2050. “This can reduce to a certain extent the exposure to heat that will be felt,” insists the researcher.