The influence of air pollution on the climate
It is not news, the emissions of many air pollutants (ozone, soot carbon, carbon dioxide, particles...) are toxic and harmful to health as well as to the environment. To better understand these interactions, let's zoom in on soot carbon (also called black carbon) and carbon dioxide - CO2 - because both contribute to the greenhouse effect.
Soot carbon, a carbon compound whose black color absorbs light radiation, can influence the radiation balance by warming the atmosphere. It is part of the PM2.5 fine particles (diameter less than 2.5 μm) and also comes from combustion engines (mainly diesel), wood and coal burning, power plants, heavy fuel oil or coal use, agricultural waste burning, and forest/vegetation fires.
An American study dating from 2013[1] highlights the extreme responsibility of soot carbon in global warming since it would be the 2nd factor after CO2. Soot carbon, present in the air as an aerosol (mixed with other particles), has a lifetime in the atmosphere of a few days to a few weeks at most; in comparison, CO2 has a lifetime of 100 years. Thus, for the same emission, soot carbon causes a heat peak over a short time, while CO2 permanently warms the atmosphere.
CO2 emissions occur naturally in the atmosphere (volcanic eruptions, plant, animal, and human respiration, natural forest fires, decomposition of dead organic matter)... However, since 1990, 70 to 90% of CO2 emissions come from the combustion of fossil fuels. Agriculture and forestry contribute 12% of carbon dioxide emissions.
It would be wrong not to consider CO2 as an air pollutant because of its natural presence in the atmosphere and its role in the life cycle. Man-made CO2 levels in the atmosphere have been steadily increasing for millions of years. A sharp increase of 30% has been observed in the last two centuries. The effects of CO2 on human health are small when it is in "natural" quantities in the atmosphere; when its concentration increases sharply, it becomes an air pollutant in the strict sense of the term [2].
Climate change: a chain of impacts
In an interview for reseauactionclimat.org[5], Isabella Annesi-Maesano, director of research at Inserm, states bluntly: "Pollution aggravates global warming and vice versa" and gives many examples: "... Global warming increases desertification, which will increase the presence of sand particles in the air. It will cause wildfires and increase air pollution." Another significant snowball effect: we know that climate change increases rural exodus and urbanization, and thus pollution!
As for the fine particles from combustion engines, it has been found for example in the polar regions, that they cover the ice and snow, darkening them slightly, which reduces solar radiation in space and contributes to global warming. Slightly warmer temperatures encourage plants in the sub-Arctic region to grow faster; when they grow in snow, they create a shadow that also darkens the earth's surface, leading to further warming.
Finally, climate change causes the pollen season to become earlier and longer. And air pollution makes the pollen more aggressive and us more sensitive to allergens. These examples are a chain of impacts on all fronts, and can be multiplied endlessly.
Sources
- [1] Research conducted by 31 scientists and published in the online version of the US journal Geophysical Research-Atmospheres.
- [2] "A biological, physical, or chemical alterogen, which above a certain threshold, and sometimes under certain conditions, develops negative impacts on all or part of an ecosystem or the environment in general." (Wikipédia.com)
- [3] Quoted in Ozone, this other underestimated pollutant, which threatens health and biodiversity: Heat wave: an ozone pollution toxic for humans (futura-sciences.com)
- [4] Methane emissions have never been so high in the world! (futura-sciences.com)
- [5] Quoted in Air pollution and warming make each other worse: https://reseauactionclimat.org/rechauffement-climatique-pollution-air/
Credit Photo "Ciels de Paris" Laurent Sacco
