Climate Feedback

Carbon dioxide – not the only culprit

Carbon dioxide usually steals the media limelight as chief climate change culprit.

But in a break with tradition, a less-recognized agent of climate change – black carbon – has been the focus of much media attention this week following a review article by V. Ramanathan and Greg Carmichael in Nature Geoscience.

Though many of the news stories have incorrectly reported this as new research, it’s actually an overview of what we know about this important agent of global warming – with some interesting insights from the authors on how it could contribute to future warming trends, and what can be done about it.

Black carbon, which is a component of soot, is largely generated from burning biofuels, biomass such as forests and crops, wood and even dung. Back in August, Ramanathan and co-authors had a paper in Nature showing that brown clouds in the atmosphere, which are largely comprised of black carbon and other aerosols, are significant contributors to regional warming over Asia, in some cases having as great an influence as carbon dioxide.

In the Himalayan region, their combined influence on long-term warming may be sufficient to account for the retreat of glaciers, as highlighted in a news feature last year on Nature Reports Climate Change.


From the Indo-Gangentic plains of South Asia to sub-Saharan Africa, the review article very nicely takes readers through the hotspots of soot-induced warming. South and East Asia are among the world’s worst affected regions. Black soot not only contributes significantly to warming here, but poses a mjaor threat to human health.

The challenge, say the authors, will be to replace biofuel cooking with options that are free from black carbon, such as solar, bio and natural gas. This seems highly feasible, given that we have the technology, as reported in the LA Times story:

Black carbon emissions in Western Europe and the U.S. have decreased about 300% in the last 30 years because of more-efficient coal combustion, a move away from wood-burning fireplaces, and cleaner, more efficient technology.

And because black carbon has a much shorter lifespan than CO2, reducing this source of emissions could provide a vital short-term option for reducing global warming…while we faff around with long-term strategies such as funding new technologies, geoengineering the earth and/or agreeing to a global climate deal.

Olive Heffernan

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