Temperatures that are cold in the back. 48°C in Italy, 40°C in the Mediterranean basin, 52.2°C in China… The northern hemisphere of the planet is currently experiencing a major heat wave, the effects of which are felt until Greenland.
Italy is suffocating and exceeded 40°C this weekend, while in Spain the ground temperature has risen to 60°C and the country sees 75% of its territory threatened by desertification. The south-east of France is not left out and should switch to heat wave alert on Tuesday. From Europe to Asia, including the United States and its 47°C, record temperatures are expected, illustrating the extreme conditions amplified by global warming. CNRS climatologist Davide Faranda explains to Le Point how such a phenomenon is possible.
???Heat wave developing in the south-east quarter over the next few days, with a peak expected on Tuesday and Wednesday.??
Le Point: How big is the heat wave currently going through the northern hemisphere?
Davide Faranda: Multiple heat waves affect the entire northern hemisphere, but the one that particularly concerns us is the unprecedented one crossing the Mediterranean. In Sicily and Sardinia, for example, we arrive at extreme temperatures for July: we do not break the records recorded in August, but to reach temperatures between 43°C and 48°C on this date is never seen.
What should also be noted is that in addition to temperature, humidity is also very important. On the Italian and French coasts, as in North Africa, the humidity rate is approaching 50%. This is unprecedented: it was recorded in August 2021, but never in July, and it is approaching the limits of what is bearable for human health, exposing it to cardiovascular risks, cardiac arrests, strokes, breathing difficulties for children… It is therefore not negligible for health. This particularly affects tourists, who are not used to high temperatures, unlike local populations.
The forecasts
What actually happens?
A high pressure area has formed over the Mediterranean. Usually, heat waves in this area are caused by air coming from North Africa, but here, and this is an anomaly, the hot air is produced locally. It’s worrying: the Mediterranean is reaching tropical temperatures, the air is stagnant and the heat is building up without even the warm air coming in from Africa. A Mediterranean anticyclone forms on its own, and becomes a local monster.
It is a new actor that causes temperatures above 40°C. This is a problem for humans, as we have seen, but also for vegetation, which is reaching its genetic limit. Above 40°C, 41°C, several species are in danger of death. Not to mention that it’s not raining, so that makes the drought worse. We are drawing from groundwater already too low to water crops, and the atmosphere in cities may be very dry, which favors the spread of fires, such as at Catania airport, where flights are canceled until to July 19. Soil moisture there is very low: parts of Sicily and Spain have been under water stress since 2017.
What is it due to? Does the El Niño phenomenon play a role?
The heat wave situation in the Mediterranean is mainly due to greenhouse gases. The role of El Niño is difficult to assess, it belongs to the list of culprits, but its role is less central than that of greenhouse gases and will undoubtedly intervene later.
It can be shown almost systematically that heat waves are increasing in intensity and duration due to climate change. Greenhouse gases, and in particular carbon, emitted by the combustion of fossil fuels, are stored in the atmosphere. They capture the infrared radiation reflected from the Earth back into space and, through a chemical reaction, send the energy back to Earth, causing warming.
This concentration of greenhouse gases also produces other effects: as increasing temperature increases pressure, areas of high pressure expand and become more persistent. It’s a “hot air balloon effect”: the increase in global temperature changes sea currents and winds, which allows the creation of more stable anticyclones, as we see now on the Mediterranean.
Why is this happening now? Was this planned by the IPCC?
It is very difficult to understand why, in recent years, we are witnessing such an increase in extreme events, far from the norm. In climate simulations, these heat waves occur from 2050 in scenarios where we continue our CO2 emissions. However, we currently have a foretaste of it. This was not planned. The mesh of the simulations for extreme events of this type is indeed global and not regional, and it does not take into account local geographical specificities, such as mountains or cities for example.
The IPCC has thus predicted that, without emission reductions, heat waves will become the norm, but these local intensities, 48°C in Sicily or 50°C in Canada, escape us for the moment, and we must work on new models. more local.
So while we have certainties, we also have a lot of uncertainties. That is why we must be careful and urgently reduce greenhouse gas emissions.
We will find ourselves in a dangerous world for life, that of humanity and that of ecosystems. As scientists, we are very worried. What we have planned is far from pleasant, and we are starting to experience it, it is frightening. It is becoming imperative to reduce our greenhouse gas emissions to maintain a viable society for the 8 billion human beings who inhabit the planet.
