Both the origin and the methodology of the weather report according to which it was 42°C in Rome on July 27, 1841 are questionable. And the occurrence, possible but unlikely, of such an event does not call into question the reality of global warming.
It’s hot, very hot, too hot. At the end of July, the northern hemisphere is suffocating, crushed by a scorching heat wave, from North America to Asia, via Europe. In France in particular, temperature records have been broken. This extreme episode comes as, globally, the month of June was the hottest on record, with an average temperature of 16.5°C on the Earth’s surface. A planetary heat record was again broken at the beginning of July, with an average global temperature exceeding 17°C.
>> Compare today’s weather to temperature history
But on social networks, very followed accounts put the seriousness of the phenomenon into perspective, claiming that scorching temperatures have already been recorded, especially in Italy, almost two centuries ago. And this, while some polluting human activities had not yet seen the light of day. A way of questioning the cause and effect link established between global warming caused by the hand of man and increasingly intense and frequent extreme weather phenomena.
A common argument from climate skeptics
This is the case of Silvano Trotta, a figure known for his conspiratorial positions. This entrepreneur, who implied for years that man has never walked on the moon, even that the Earth satellite is hollow, saw its notoriety grow during the epidemic of Covid-19, during which it propagated many conspiracy theories on the origin of the virus or the vaccines. Now he comments on the war in Ukraine and the weather. In a tweet posted Monday, July 17, he writes that he was already doing “42°C (in the shade) July 27, 1841”. “And back then, without cars, freighters, planes, etc.”, he adds.
Silvano Trotta echoes the words of a certain Robin Monotti, an Italian architect and film producer. In a tweet published on Sunday July 16seen more than 3.5 million times, Robin Monotti already claims that he was doing “42°C in Rome in July 1841”, “before cars and planes” And “unrelated to CO2”. He specifies that his photo is purely illustrative.
In his tweet, the Italian cites his source: an article from meteolive.it, the site of an Italian company specializing in weather forecasts. This article compiles information disseminated on the forum of the site, concerning “Rome weather records”. On this forum, an Internet user using the pseudonym “tempus140” published the following message on December 28, 2015, in Italian: “To tell the truth, the record of 42°C of July 17, 1841 would remain unbeaten, which is however not recognized, because it is not in conformity with what was recorded by other mysterious weather stations of the time.”
Data from a dubious source
Where did this Internet user get this information? In the meteolive.it article it is mentioned that the record temperature “was recorded from the Roman College station, located in the historic center of the city” from Rome. The Roman College weather station “records meteorological data from the center of Rome continuously since 1782”specifies the site of mItalian Ministry of Agriculture, Food Sovereignty and Forests. It is therefore possible that temperature readings were taken in 1841 in the Italian capital.
However, studies on temperature records in Rome do not go back beyond 1862, the first year of publication of the Meteorological Bulletin of the Observatory of the Roman College, available in the catalog of the National Library of France. A little-known Italian blog, which has just over 330 followers on Facebook, has however embarked on the exercise of expanding the database, by integrating older unofficial temperature readings. This blog mentions “the maximum temperature of +42.0°C on 07/17/1841 reported in certain sources consulted”. But he specifies that this statement “is incompatible with the maximum temperatures recorded simultaneously by other meteorological stations”, without however specifying which ones. An assertion then taken up on Wikipedia, where the blog is cited as a source of the article devoted to the weather station of the Roman College.
A non-standard statement
According to Joël Guiot, paleoclimatologist and emeritus research director at the CNRS, interviewed by franceinfo, it is unlikely, even if not impossible, that it was 42°C in Rome in July 1841, because at this time “Europe is experiencing a Little Ice Age, due to intense volcanic activity”. Moreover, “temperature readings are not more or less reliable until 1950”, underlines the expert. Even if a thermometer had recorded 42°C in Rome in 1841, this temperature could not therefore be compared with current temperature readings.
Because measuring the temperature is not as simple as it seems. To obtain standardized, comparable data, they must be collected under specific conditions, using a meteorological shelter. “Ihe presence of heat sources, cast shadows and uneven ground can disturb the measurement by creating parasitic radiation”, explains Météo-France, in an article devoted to the constraints of installing a meteorological shelter. This last “must be placed 1.50 m above a lawn”further illustrates paleoclimatologist Joël Guiot.
You have surely already noticed a difference of several degrees between the temperature displayed on a pharmacy sign and the official temperature. It is enough that the thermometer of the sign is in full sun, or on the contrary in a shaded alley, so that the temperature recorded is different. In addition, in the city, heat island phenomena can change the temperature from one street to another, depending on exposure to the sun, street materials, vegetation present, etc. “On concrete, the temperature rises. If you replace the asphalt with another material, you can lose several degrees”explains J.Oel Guiot.
Real global warming
Let’s admit that it could have been 42°C in Rome in July 1841. “Extreme, exceptional events, there may have been”, recognizes Antoine Nicault, coordinator of the Regional Group of Experts on the climate in the South Provence-Alpes-Côte d’Azur region (Greek-SUD). However, “on average, it has never been so hot. Currently, almost the entire northern hemisphere is in a heat wave, and it now happens every year.he warns. Heat waves are increasingly frequent, early, long and intense. The problem is the trend towards an increase in these extreme events.” Un isolated event in the past cannot, on its own, call into question the very clearly established scientific consensus of the existence of global warming.
>> Our answers to your questions on global warming
As for the human origin of global warming, this is also very clearly proven by the numerous scientific studies and the various reports of the IPCC, the international group of experts on the climate. “Natural effects cannot explain global warming”, insists Joël Guiot. An argument often used by climate skeptics is, for example, that of warming due to solar activity. The paleoclimatologist is however categorical: “Iactivity of the Sun is absolutely not significant in explaining global warming.” On the other hand, the “cars, freighters and planes”, listed by Silvano Trotta, are partly responsible for the warming of our planet. Transport alone was responsible for 25% of CO2 emissions due to the combustion of energy in the world in 2018, according to data from the International Energy Agency, cited by the Ministry of Ecological Transition.