“In 1152, the heat was so intense that you could cook eggs in the sand. (…) In 1303 and 1304, the Seine, the Loire, the Rhine and the Danube could be crossed on foot. (…) In 1748, 1754, 1760, 1767, 1778 and 1788, the summer heat was excessive. » With each heat wave, 2019in 2020 and now in 2022the same text is circulating on blogs or on Facebook in an attempt to demonstrate that the current periods of heat wave are not exceptional.
What the publication says
This enumeration, copied many times, would have appeared in an English newspaper, the Hampshire Advertiser of Southampton, July 17, 1852”. In fact, the British weekly had already taken up an article from the French news daily in English, the Galignani’s MessengerJuly 12, 1852. The newspaper then drew up a list, rather imprecise in places, of known heat waves in the past.
“It is indeed an extract from a newspaper from 1852 and not from some conspiratorial site”, insists the Facebook post. For those who describe themselves as “climate realists”all these examples of “extreme heat waves” and of “catastrophic droughts”, “at a time when there was not yet the slightest hint of the beginning of the industrial revolution” show that, “Obviously, there is nothing new under the sun”.
According to this viral text, historical examples would prove that human-caused global warming is not involved in the current heat waves and that these are nothing extraordinary. In their arguments, these climatosceptics invoke an interview with historian Emmanuel Le Roy Ladurie given to Release during the heat wave of 2003. This recognized specialist in the history of the climate then relativized “the news of a hot summer”explaining that “this kind of great drought has not been lacking in French history”, and quoting “series of consecutive scorching summers, climatic microeras: 1331-1334, four summers in a row, 1383-1385, three summers”. He also remembered the death ” spectacular ” scorching summers of the pre-industrial era, citing the figure of “700,000 dead” over the period 1718-1719.
Why is this misleading
If periods of heat wave are not lacking in history, they must, however, be recontextualized. “In all eras, people have experienced heat waves, but they are always relative to the average climate of the time in question and these average temperatures have greatly increased today”explains Françoise Vimeux, climatologist at the Research Institute for Development (IRD).
The scientist cites the heat waves that affected Paris at the beginning of the 17th century.e century. It is possible to rely on the series of monthly temperatures in the Paris region since 1676, compiled by meteorologist Daniel Rousseau, from information left by scientists or newspapers of the time, and cross-checked with the dates of the harvest. In 1705, average temperatures from June to August were 18.9°C. In 1706 and 1707, they were 19.7°C, which made them, at the time, summers considered abnormally hot.
In comparison, the summer of 2021, which has not experienced any severe heat waveexceeded the levels of two centuries ago, with an average of 20.2°C in Paris between June and August. “These heat waves weren’t as frequent, not as long and not as intensesupports Françoise Vimeux. They were not so out of the norm compared to the average temperatures of the time. »
“The current warming goes far beyond”
In the same interview with Release quoted by the viral publication, Emmanuel Le Roy Ladurie, far from denying the current climate change, affirmed on the contrary that “the aggravation [actuelle] of the greenhouse effect phenomenon is a break in the history of the climate which can open a new climatic era with one or two degrees of difference. This would have incalculable consequences. »
In another interview, in 2009 in the magazine Perspectives on the economythe historian also dismissed the theory of a return to the small medieval optimum (POM) – also called “medieval climatic anomaly” – during which Western Europe experienced slightly milder temperatures, between the year 900 and the year 1250. “The current warming goes far beyond”he supported, arguing:
“At the height of the POM, average temperatures were – in Scandinavia at least (…) – 0.7°C higher than their Little Ice Age minimum. In 2001-2007, we gained 1.6°C in France compared to the beginning of the 20th century.e century… Of course, we don’t know everything. In particular, it is absolutely not proven that the first warming (1911-1950) is linked to CO2. For the second (post 1986), there is hardly any doubt. »
As for the number of “700,000 dead” of the summers of 1718-1719, mentioned by Mr. Le Roy Ladurie in 2003, it is certainly impressive, but it does not prove either that heat waves were more serious in the past, because sanitary conditions have evolved over two centuries. “At the time, mortality was mainly due to the spread of epidemics, dysentery or typhoid fever, due to the consumption of unsanitary waterrecalls climatologist Françoise Vimeux. In the XVIIIe century, there was no infrastructure that makes us today much less vulnerable to a shortage of drinking water. » Despite heat records never reached in Europe, the heat wave of 2003 thus caused ten times fewer victims (70,000 deaths, according to Inserm) than those, weaker, of 1718-1719.
Source: Le Monde