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Air pollution and global warming: one affect the other like interconnecting pipes

For some time now, we have been aware, identifying, and studying the interconnections between climate change and air quality; they certainly exist but are complex. At the beginning of this summer, the effects of global warming are on everyone's mind, what about the effects of it on air pollution? How can we reduce the impact on one another? Rest assured, we will answer all these questions.

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].

And what about ozone?

Ozone is an odorless and colorless gas that plays an extremely toxic role, particularly for plants, which makes them more vulnerable to disease and drought. It represents a real danger to biodiversity. However, its concentration is strongly increasing under the effect of global warming: a snowball effect still largely underestimated at the worldwide level. It is also a powerful greenhouse gas. Ozone is well-known for its harmful effects on human health. According to the European Environment Agency (EEA), ozone exposure was responsible for nearly 20,000 premature deaths across the European Union (EU) in 2018, up from about 16,000 in 2009, an increase of nearly 25 percent.[3]

Global warming is making this scenario worse. According to Daniel Jacobs, professor of atmospheric chemistry at Harvard University, "Warming induces more stagnation and accumulation of polluted air, the reactions that make ozone occur more rapidly, and nitrous oxide (one of the precursors of ozone) has a longer life span at warmer temperatures."[4] The warming of the atmosphere is also causing more pollution. Emissions of methane, another ozone precursor, have also increased by nearly 10% in the last 20 years.

Global warming: 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 global warming increases rural exodus and urbanization, and thus pollution!

Comparaison de pollution à Paris

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, global warming 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.

The double positive impact of solutions

The good news is that since global warming and air pollution are linked, solutions against air pollutants could have almost "automatic" impact on climate change. Especially if fast action is taken to reduce some extremely potent but short-lived pollutants (ozone, carbon dioxide, black carbon, etc.), it could have a decisive impact on global warming and avoid dangerous tipping points.

In the context of climate change, it is crucial that policies to mitigate emissions of air pollutants and greenhouse gases be coordinated. It is, therefore, necessary to promote "integrated" policies, i.e. policies that are winning on all fronts and that are co-beneficial for health. This will allow us to be more effective in improving air quality in the short term while limiting the negative effects of climate change in the longer term.

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

 

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