Deadly Super-Pollutant Black Carbon Has Evaded Global Attention So Far

DUBAI, United Arab Emirates – Black carbon is a super pollutant and its emissions are commonly seen anywhere you see black smoke – from a tiny kerosene lamp to a massive ship. The main sources include the burning of biomass, garbage dumps, diesel vehicles, coal-fired power plants, brick kilns, wood fires, wildfires and, on the high seas, ships.

Superpollutants are sometimes referred to as short-lived climate pollutants. Black carbon (BC) has a lifespan of just one or two weeks before it falls to the earth, in comparison to carbon dioxide which has a lifespan of a few hundred years in the atmosphere. 

But in this short span, its effects are devastating. Conversely, cutting its emissions can lead to rapid health and climate action benefits. 

Jane Burston is the CEO of Clean Air Fund (CAF), one of the four organisations that produced the report, The Case For Action On Black Carbon,  that was launched at COP28 over the weekend.

The other organisations were the Center for Study of Science, Technology, and Policy (CSTEP); Berkeley Air Monitoring Group, and Orbis Air.

She explains why, despite its short lifespan, BC’s global warming potential is as bad as carbon dioxide, the biggest contributor to climate change. 

It’s black, so when it’s in the atmosphere, it radiates. It captures energy from the sunlight and radiates heat into the atmosphere. So even though it only stays in the atmosphere for up to a couple of weeks, it has a very high global warming potential. While it’s there, it’s as bad as a ton of carbon dioxide.”

Jane Burston, CEO of Clean Air Fund.

Threat to Polar Ice Caps, Himalayas, Andes 

While BC affects its immediate area the most, in the right conditions it can spread very far. It covers polar ice caps and glaciers in soot which in turn absorb more heat and trigger more melting. 

The retreat of the Himalayan glaciers has accelerated by 50% between 2012-14 because of BC warming and snow darkening, which in turn affects the monsoon. 

It causes a different type of cloud formation and changes rainfall patterns. So we’ve seen black carbon in India changing monsoon rainfall pattern and in West Africa the Sahel similarly,” Burston told Health Policy Watch.

It’s not just Himalayan glaciers retreat that BC has been linked to, the report says it decreases Arctic sea-ice cover in summer, advances the western United States melting season, and increases run-off in the Andean glaciers.

Panel at COP28 on black carbon: (L-R) Dr Indu K Murthy, (CSTEP), Nina Renshaw (CAF), Michael Johnson (Berkeley Air Monitoring Group) and Paula García Holley (Clean Air Task Force).

Health impacts of black carbon

BC contributes to a significant chunk of PM 2.5, or particulate matter with a diameter of 2.5 microns or less which is microscopic. PM 2.5 is usually the most tracked air pollutant, according to the report. 

Annual deaths due to fine particulate and ozone air pollution are estimated to be 8.34 million, which is more than one in 10 deaths, according to a recent report in the BMJ. More than half (52%) of these deaths are due to heart attacks, strokes and pulmonary diseases including cancer. 

“The highest total attributable mortality occurs in China, with 2.44 million deaths per year, followed by India with 2.18 million deaths per year.” according to the BMJ, November, 2023.

BC is strongly correlated with increased blood pressure levels, a high-risk factor for cardiovascular disease and strokes. It affects pregnant women and has been linked to low birth weight. 

While it’s not clear exactly how many premature deaths are linked to black carbon, the report assumes two scenarios. If BC is assumed to be equally toxic as other PM 2.5 components then it is associated with 150,000 deaths worldwide. But if BC is “significantly” more toxic then widespread reduction of BC emissions has the potential to reduce premature mortality by as much as 400,000 annually over North India’s Indo-Gangetic Plain alone. 

Aerial view of a wildfire.

“I’ve been working on a study of household air pollution intervention that we’re proud of as it is the biggest randomised control trial looking at the health effects of transitioning from biomass stoves to clean cooking LPG,” said Michael Johnson, technical director of Berkeley Air Monitoring Group. “And we found the effects on birthweight to be more strongly linked with black carbon than with PM 2.5.”

Nina Renshaw, CAF’s head of health, has studied BC for two decades: “The thinking is that the black carbon within PM 2.5 may be actually more harmful than other components of PM 2.5. There’s still research to be done in that area. But what we do know is that black carbon is particularly damaging for cardiovascular health – heart attacks, disease, strokes, neurological damage, and so on. Black carbon has also proven to have an impact during pregnancy and birth outcomes, low birth weights and so on.”

‘No brainer’ – start cutting black carbon now 

The new report on black carbon fills a vacuum as there has been far less work on it than carbon dioxide, ozone and PM 2.5. There hasn’t been much global monitoring and there ought to be more studies on epidemiological evidence and toxicology for air quality regulations.

R Subramanian from the Center for Study of Science, Technology, and Policy (CSTEP)

R Subramanian, head of Air Quality at the Center for Study of Science, Technology, and Policy (CSTEP), Bengaluru, told Health Policy Watch: “As we are moving closer to the climate tipping points, we need more levers that we can control to avoid reaching those tipping points.” 

Renshaw says it’s a “no-brainer” to include cutting black carbon emissions as part of programmes to cut PM 2.5.

“Working on particulate matter, PM2.5 in particular, is a no-brainer. That is a WHO guideline, the International Agency on Cancer Research (IARC) says that this is carcinogenic and so on. We can begin to capture black carbon and do that. So let’s go down that route as an urgency and fill up the gaps as science allows.”

Indu K Murthy, CSTEP’s head of Climate, Environment, and Sustainability,  highlights another route, via government regulation: “We’re talking about cleaner energy and clean air which is a mandate of every government in any case. And you just have to kind of bundle it along with that till we get the metrics right.

Image Credits: Nick Sorockin/ Unsplash, Marc Szeglat/ Unsplash.

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