Over 50°C in Morocco, 53.3°C in Death Valley, 31 consecutive days over 43°C in Arizona and Dantean fires in Canada and Greece. The summer of 2023 was marked by a dismal litany of records and climatic catastrophes. While average global temperatures in June, July and August had already been classified in September as the highest since recording began at the end of the 19th century, a study published Tuesday, May 14 in the journal Nature went even further. The summer of 2023 turned out to be the hottest ever recorded for 2000 years in the northern hemisphere outside the tropics. It exceeded the average summer temperature for this period by more than 2°C, and even its hottest summers by more than 1°C.
"I didn't expect such exceptional results. A milestone has been reached," said Jan Esper, the study's lead author and a geographer at Johannes-Gutenberg University in Mainz, Germany. The cause is climate disruption due to human greenhouse gas emissions (mainly from the burning of coal, oil and gas), compounded by the natural phenomenon of El Niño, a warming of the equatorial Pacific Ocean that usually results in a rise in the global thermometer. These results clearly demonstrate "the unparalleled nature of current present-day warming," reinforcing "the urgency" to achieve carbon neutrality, the scientists wrote.
"This robust and original study confirms the unprecedented nature of recent warming, with a very clear result for last summer at these latitudes," said climatologist Valérie Masson-Delmotte, who was not involved in the study. The latest report by the Intergovernmental Panel on Climate Change (IPCC) already showed that the rate of global warming over the last 50 years was unprecedented for more than 2000 years. But the exercise had never been carried out for a record summer in particular.
To arrive at these results, the authors proceeded in two stages. Using temperature measurements at the Earth's surface from several thousand weather stations in the northern hemisphere, aggregated by the Berkeley Earth non-profit organization, they first showed that the months of June, July and August 2023 were 2.07°C warmer than the average of other summers from 1850 to 1900, commonly considered to be the pre-industrial era.
However, this dataset presents "high uncertainties" with regard to the oldest measuring instruments, said the study. The period 1850-1900 was only covered by 58 weather stations, 45 of which were located in Europe. "Some values were also distorted during this period, as they were obtained from thermometers that were left in direct sunlight instead of being placed in the shade," said Esper.
You have 54.7% of this article left to read. The rest is for subscribers only.