Aren’t greenhouse gases 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 has increased from 285 parts per million (ppm) to 426.95 ppm as of June 26. The curve of the increase in temperatures follows almost identically that of the concentration of carbon dioxide (CO2).
See a NASA animation showing global warming since the pre-industrial era
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 atmosphere. 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 happens after a volcanic eruption that releases large amounts of sulfur dioxide into the atmosphere,” adds Kent Moore, a professor at the University of Toronto and climate change expert.
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 been ‘cooling the planet while we are warming it’. I deduce that in the end, the temperature has not changed. Excellent news! Now, all that remains is to eliminate all the taxes we pay in the name of ‘fighting climate change’.”
Is it true that the temperature hasn’t changed?
That’s not true. Aerosols have sort of masked global warming, but the planet has been warming since the beginning of the pre-industrial era, says Kent Moore. “Aerosols have helped us in the last few decades by masking warming. If we take them away, we’ll get more warming.”
How much greater would this warming be without these aerosols?
There doesn’t seem to be a consensus on the issue. “We’re in a very deep uncertainty zone. It could be a full degree of masked cooling,” climate scientist 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 about 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 the lifetime of CO must also be taken into account.2 and 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.