Why we must attack black carbon air pollution to protect the climate

Anyone driving behind an old diesel truck going uphill has seen – and smelled – one of the most important yet neglected causes of climate change. The dark cloud streaming out of its tailpipe is full of black carbon, often known as soot.

Pound for pound black carbon is 1,500 times more powerful than CO2 in heating the planet. It’s particularly devastating in the Arctic, where it helps drive warming four times faster than the global average. It also contributes to over 10 million deaths every year from fossil-fuelled outdoor air pollution and indoors from dirty cooking fuels.

Yet, it holds the key to preventing climate change from escalating. It is one of four short-lived super pollutants that drop out of the atmosphere fast when no longer emitted, enabling the rate of warming to be rapidly reduced.

Methane, hydrofluorocarbon refrigerants, ground-level ozone and black carbon account for nearly half of today’s warming. Slashing them through available, cost-effective measures cuts the rate of global warming by half and two-thirds in the Arctic.

Reducing CO2 takes a long time to take effect because some of it remains in the atmosphere for centuries. The short-lived pollutants, by contrast, can fall out within days or up to a decade and a half. Tackling them simultaneously avoids four times more warming by 2050 than cutting CO2 alone.

This is important because the world is locked in two races against time. The first is the familiar decades-long marathon to decarbonize the world’s economies. But we also need to win a near-term sprint if we are to limit exceeding the 1.5 degrees Celsius danger level, beyond which await a series of irreversible and potentially catastrophic climate tipping points. Cutting fast-acting super pollutants is the only way to win the sprint.

Unlike the other super pollutants, black carbon is not a gas but a form of particulate matter released by burning fossil fuels, wood and other biomass. It falls out within five days. When it does so in the Arctic, it darkens reflective snow and ice, causing them to absorb heat instead, accelerating warming and melting in a self-amplifying feedback loop.

Until recently, the Arctic has served as an essential line of defence against global warming since it safely reflects so much solar radiation back into space. But half of the reflective summer sea ice is gone; when the rest goes, it will add 25 years’ worth of current CO2 emissions to warming.

Tackling black carbon is a quick“win-win” on climate and air quality. Solutions exist to cut 70% of its emissions by 2030. They include reducing diesel emissions from transport, swapping out biomass fuels for cleaner cookstoves and banning heavy fuel oil in the Arctic.

Given the importance of the Arctic in regulating climate change, we need to move immediately to protect this region from black carbon. The Arctic Council set a voluntary target of a 25-33% reduction below 2013 levels by 2025. Member countries are on track to meet it collectively, even though Russia is lagging.

Many governments are also starting to include the super pollutants in their voluntary nationally determined contributions to cut emissions under the Paris Agreement. Methane emissions are being addressed under the voluntary Global Methane Pledge.

But voluntary promises are not enough. We need mandatory action. Some places have succeeded in reducing black carbon through air pollution laws. California has been a pioneer, while the US Clean Air Act has had success at the federal level. Similarly, the UN Economic Commission of Europe has a long history of reducing air pollution under the Convention on Long-Range Transboundary Air Pollution. Hydrofluorocarbon refrigerants are being reduced under the mandatory phasedown schedule of the Kigali Amendment to the Montreal Protocol.

We need a similar mandatory approach to the superpollutants. A mandatory agreement for black carbon would be a good start, focusing initially on the Arctic and South Asia, a black carbon hot spot with teleconnections to the Arctic. Melting Arctic ice can drastically weaken ocean currents, causing faster sea-level rise across the US East Coast and parts of Europe and leading to erratic and unsustainable changes to the Indian summer monsoon, which supports the livelihoods of one billion people. Unless we protect the Arctic, there’s a risk that its teleconnections will cause irreversible and extreme changes worldwide.

Until the Global Methane Pledge, international climate efforts focused almost exclusively on CO2. It’s time to appreciate the super pollutants so we can win the sprint as well as the marathon. All countries can start by including the super pollutants in their next nationally determined contributions in 2025.

It would help to use separate metrics to track CO2 and the short-lived climate pollutants – as they operate on different timescales – instead of lumping them together, as at present. This would help policymakers understand the unique damage the super pollutants cause, for example, in the Arctic and the unique opportunity they offer for slowing warming in the near future, leading to more effective target-setting.

We can see the climate emergency in the drumbeat of unnatural disasters with their growing price tags and the human suffering they impose. Heatwaves kill nearly 500,000 people every year while worsening air pollution. And every tenth of a degree of warming increases the risk of passing irreversible and catastrophic tipping points.

Drastically cutting black carbon and other climate super pollutants is the only known way to slow warming in the near term and we need to exploit this advantage to the fullest.

Alyssa Hull, research associate at the Institute of Governance, also contributed to this article.