28-04-2025
The world is waking up to the dangers of superpollutants
Carbon dioxide is the big daddy of greenhouse gases. Making up the bulk of our emissions and staying up in the atmosphere for many centuries, whether we're successful or not at limiting global temperature rise boils down to what we do about CO2.
But it's only part of the equation in global warming. A group of lesser-discussed climate pollutants are many times more powerful than carbon dioxide and could serve as an emergency brake on near-term warming. Even better: There's reason to be cautiously optimistic.
So-called super pollutants — a group of greenhouse gases and aerosols including methane, black carbon, hydrofluorocarbons (HFCs) and tropospheric ozone — are responsible for about 45% of warming to date, with carbon dioxide responsible for the other 55%. While these emissions exist in the atmosphere for a fraction of CO2's centuries-long lifetime, they have a more potent warming effect.
Methane is the short-lived climate pollutant with the greatest impact, coming mainly from agricultural, waste and oil and gas industry sources. While methane isn't toxic in itself, it's the primary contributor to tropospheric — or ground-level — ozone. O3 is actually helpful when it's up high, 20-odd kilometers above sea level, where it filters the sun's ultraviolet radiation; but down in the lowest level of our planet's atmosphere, it wreaks havoc with our lungs and vegetation.
Black carbon — the soot that results from incomplete combustion of fossil fuels, waste and biomass — isn't a greenhouse gas, but does contribute to warming by absorbing sunlight and releasing it as heat, in the same way that urban infrastructure and asphalt roads do. As a major component of particulate matter, black carbon is bad news for our respiratory and cardiovascular systems and impedes photosynthesis in plants.
As these pollutants disappear from the atmosphere much faster than CO2, the benefits of reducing them will be realized sooner. Chris Malley, senior researcher at Stockholm Environment Institute, explained that hasty mitigation has the potential to slow down the warming expected by 2050 by as much as 0.5 degrees Celsius. But the real beauty of reducing super pollutants is the benefit to human health and food security: The Clean Air and Climate Coalition, a body launched by the United Nations Environment Program, states that it could also prevent more than 2 million premature deaths each year and avoid annual crop losses of over 50 million metric tons.
Despite their multihazardous natures, the Paris Agreement doesn't require countries to single out super pollutants in climate action plans known as nationally-determined contributions, or NDCs. As a result, many of the first NDCs didn't do so at all, simply referring to one number — CO2-equivalent, a standardized metric which converts the different warming potentials of each pollutant into a comparable figure. This doesn't give a clear picture of the impacts of any given action plan as these gases have distinct impacts over different timescales. It also obscures the chance to communicate the very tangible and near-term public benefits.
But here's why we ought to feel some optimism. NDCs are submitted every five years and in the second round of submissions post-2020, Malley observed a sizeable uptick in countries referring to super pollutants explicitly or implicitly, via sector-specific targets or co-benefits. Pre-2020, only Mexico and Uruguay included quantitative reduction targets for a relevant super pollutant. Post-2020, 20 NDCs included quantitative information on short-lived climate pollutants or air pollutant reductions.
It's also notable that several countries also included assessments of the benefits. Nigeria, for example, concluded that if its climate plan was successfully implemented, 30,000 Nigerians wouldn't die prematurely every year by 2030. It turns NDCs into plans to protect citizens' health.
Now, new NDCs are being submitted ahead of the 30th United Nations climate change conference in Brazil at the end of the year. There's only a small basket to analyze, with just 19 nations submitting updated plans so far, but there are signs that awareness of super pollutants is growing.
One notable example is Canada's NDC, which reported the outcomes of a public engagement push. About 11,000 participants were asked which co-benefits of climate change action should be prioritized and 79% said air quality and public health. This demonstrates how the near-term benefits of tackling superpollutants can strengthen and broaden public support for climate action. At a time where the concept of net zero emissions is heavily politicized, that's incredibly helpful.
But, while there's reason to hope, NDCs are just pieces of paper. The U.S. submitted an ambitious climate plan at the end of the Biden administration which won't be implemented under U.S. President Donald Trump, who is withdrawing the country from the Paris Agreement again. Success in many developing countries' plans also depends on conditional support. Without more money and expansions in technical and human capacity, all the benefits for planet and people won't be realized. Methane emissions have also continued to rise, meaning that while the plans and awareness are there, we're still way off track.
We don't have to be. Often solutions are easy wins with no technical breakthroughs required, such as reducing methane leaks from oil and gas infrastructure or draining rice paddy fields once or twice a year. Economic benefits are another upside, giving the waste sector an opportunity to generate profits out of rubbish by selling compost or biogas.
Make no mistake, carbon dioxide is the number one greenhouse gas to conquer. But ridding ourselves of super pollutants will yield immediate benefits — cooling our cities, giving us cleaner air to breathe and better food to eat.
Lara Williams is a Bloomberg Opinion columnist covering climate change.
