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 are successful or not at limiting global temperature rise boils down to what we do about carbon dioxide.
However, it is 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 is reason to be cautiously optimistic.
So-called super pollutants — a group of greenhouse gases and aerosols including methane, black carbon, hydrofluorocarbons and tropospheric ozone — are responsible for about 45 percent of warming to date, with carbon dioxide responsible for the other 55 percent. While those emissions exist in the atmosphere for a fraction of carbon dioxide’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 is not toxic in itself, it is the primary contributor to tropospheric — or ground-level — ozone. Ozone is actually helpful when it is up high, about 20km 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 — is not 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 those pollutants disappear from the atmosphere much faster than carbon dioxide, the benefits of reducing them would be realized sooner. Stockholm Environment Institute senior researcher Chris Malley said that hasty mitigation has the potential to slow down the warming expected by 2050 by as much as 0.5°C. However, 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 UN Environment Program, states that it could also prevent more than 2 million premature deaths each year and avoid annual crop losses of more than 50 million metric tonnes.
Despite their multi-hazardous natures, the Paris Agreement does not 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 did not do so at all, simply referring to one number — carbon dioxide-equivalent, a standardized metric which converts the different warming potentials of each pollutant into a comparable figure. That does not 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.
However, here is why we ought to feel some optimism. NDCs are submitted every five years, and in the second round of submissions post-2020, Malley said he observed a sizeable uptick in countries referring to super pollutants explicitly or implicitly, via sector-specific targets or cobenefits. 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 is 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 would not 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 UN climate change conference in Brazil at the end of the year. There is 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 cobenefits of climate change action should be prioritized, and 79 percent said air quality and public health. That demonstrates how the near-term benefits of tackling super-pollutants can strengthen and broaden public support for climate action. At a time where the concept of net zero emissions is heavily politicized, that is incredibly helpful.
However, while there is reason to hope, NDCs are just pieces of paper. The US submitted an ambitious climate plan at the end of the administration of former US president Joe Biden, which would not be implemented under US 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 would not be realized. Methane emissions have also continued to rise, meaning that while the plans and awareness are there, we are still way off track.
We do not 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. However, ridding ourselves of super pollutants would 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.
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