Could reducing greenhouse gases (GHGs)… accelerate global warming? A counterintuitive idea, but very real. As we reduce our polluting emissions, we also reduce the aerosols that help cool the atmosphere. Explanations.
Published at 1:52 a.m.
Updated at 9:00 a.m.
Aren’t GHGs supposed to be the cause of the global warming we are currently experiencing?
This is still the case. Human activities that cause greenhouse gas emissions are still the main cause of the warming observed since the beginning of the pre-industrial era. Between 1850 and 2024, the concentration of CO2 in the atmosphere went from 285 parts per million (ppm) to 426.95 ppm as of June 26. The curve of rising temperatures also follows almost identically that of the concentration of carbon dioxide (CO2).
Watch a NASA animation illustrating global warming since the pre-industrial era (in English)
Visualize the evolution of CO levels2 in the atmosphere (in English)
But if I understand correctly, our polluting emissions are warming the planet while cooling it at the same time. Is that new?
No, this is not new. When we burn coal or oil, we also release sulfur dioxide (SO2) in the air. However, sulfur dioxide plays a cooling role by blocking the sun’s rays, explains Alejandro Di Luca, professor in the department of Earth and atmospheric sciences at UQAM.
“It’s the same phenomenon that occurs after a volcanic eruption which releases significant quantities of sulfur dioxide into the atmosphere,” adds Kent Moore, professor at the University of Toronto and specialist in climate change.
Sulfur dioxide is also a major source of air pollution and has impacts on human health. In China, for example, sulfur dioxide emissions have been reduced by more than 70% since 2005. The same scenario is true for naval transport, where new standards that came into force in 2020 have reduced emissions of this pollutant by 80%. In short, this is the perfect example of a complex issue that cannot be confined to simplistic answers.
If it’s not new, why talk about it now?
A recent report from Washington Posttitled “We’ve accidentally cooled the planet – and it’s about to stop,” addressed the topic of aerosols like sulfur dioxide and their cooling effect. The text has been picked up by several climate skeptics, who basically argue that we should continue to burn oil because it helps cool the planet…
Read the article from Washington Post (in English; subscription required)
Columnist Nathalie Elgrably also shared the report of Washington Post on the X network writing: “So, we have “cooled the planet while we warm it”. I deduce that in the end, the temperature did not change. Excellent news ! Now all that remains is to remove all the taxes we pay in the name of “fighting climate change”. »
Is it true that the temperature hasn’t changed?
It’s wrong. Aerosols have somewhat masked global warming, but the planet has indeed warmed since the beginning of the pre-industrial era, says Kent Moore. “Aerosols have helped us in recent decades by masking warming. If we remove them, the warming will be greater. »
How much greater would this warming be without these aerosols?
There does not appear to be any consensus on the issue. “We are in a very deep zone of uncertainty. It could be a full degree of masked cooling,” climatologist Zeke Hausfather told the Washington Post.
“The magnitude of the cooling associated with our emissions of sulfur dioxide and other aerosols is one of the greatest uncertainties in the climate system and has big implications for how much warming we will experience in the future as we clean up and emissions decline,” Hausfather added on X on June 25.
Alejandro Di Luca, for his part, refers us to the most recent IPCC report, which estimated in 2021 that sulfur dioxide had a cooling effect of around 0.5 degrees. According to Kent Moore, warming could be up to 40% greater without these aerosols.
View a graph showing the anthropogenic factors causing global warming
So, by reducing our emissions, it is true that we are accelerating global warming…
In the short term, this is indeed the case, experts argue. But we must also take into account the lifespan of the CO2 one you SO2 in the atmosphere, says Alejandro Di Luca. “The CO2 “will remain in the atmosphere for hundreds of years, while for sulfur dioxide it is much shorter,” he adds, specifying that the effect of these aerosols on the climate will fade more quickly than in the case of CO2.
There is also uncertainty about how the climate will respond to these different aerosols, experts agree. “Our best solution is to reduce our emissions. If we continue to burn fossil fuels, the planet will continue to warm,” says Kent Moore.
