Black carbon: When climate change and air pollution collide

I’m guessing you’ve never heard of black carbon, but surely you’re familiar with soot, yes? Well, that’s essentially black carbon. So what does soot / black carbon have to do with climate change? As it turns out, quite a lot.

Where does it come from?

Black carbon comes from the incomplete combustion of fossil fuels (e.g., coal), biofuels (e.g., ethanol), and biomass (e.g., wood—anything from fireplaces to forest fires). In developed countries, the majority of black carbon emissions come from burning diesel fuel (think: cars and other forms of transportation). In developing countries, however, most black carbon comes from residential cooking and heating (picture women crouched over charcoal cookstoves, because in addition to being an environmental issue, this one’s also a gender and health issue).

How does it work?

Black carbon contributes to global warming both directly and indirectly. Directly in that its little particles, being black, absorb sunlight in the atmosphere and turn that into heat. And indirectly because when deposited on snow and ice, black carbon reduces their reflectivity, so more heat gets absorbed (rather than reflected back into space), making the snow and ice melt faster. The resulting water, being darker in colour, absorbs even more heat, and on and on it goes (remember, we covered this back when we talked about sea ice decline). This makes black carbon a really important driver of climate change in the Arctic.

Timing is everything

Along with a handful of other substances, black carbon is part of a group of super pollutants that, molecule for molecule, punch above their weight in terms of contributing to climate change. These super pollutants are known as short-lived climate pollutants (SLCPs). The “short-lived” part is important: unlike greenhouse gases (GHGs) like carbon dioxide, which can stay in the atmosphere for hundreds of years, SLCPs have a much shorter atmospheric lifespan (more in the order of days to weeks). This timescale aspect is key. When we reduce emissions of normal GHGs, there’s quite a lag before we see anything happening in terms of falling atmospheric GHG concentrations; what we’ve already put up there stays around for a looooooong time (essentially forever), so there’s no immediate gratification for the fruits of our mitigation labours. But reducing black carbon and other SLCPs has a much more immediate impact because of their short lifecycle. While it remains imperative that we address GHGs writ large, action on SLCPs can buy us a little bit of time and might help avoid those nightmarish scenarios of unchecked climate change.

But you know what’s also great about dealing with black carbon? It’s a local pollutant (soot’s not super great for your lungs, among other things), so in addition to seeing very tangible, short-term global effects in terms of climate change, you also see immediate local public health benefits in terms of things like asthma and other respiratory conditions (and, as mentioned above, in developing countries there’s also a gender angle). That’s a lot of bang for our mitigation buck!

A no-brainer, but not a silver bullet

Now, on my more cynical days, I am sometimes inclined to think that developed countries find dealing with SLCPs an attractive option because it acts as a bit of a smokescreen (*groan*…sorry, I couldn’t resist) in that a lot of the work can be done outside their borders. They pull together some money for cleaner-burning stoves in developing countries, thereby appearing to be benevolent AND serious about dealing with climate change, but they essentially allow themselves to delay taking ambitious action at home, which would inevitably involve taking a long, hard look at fundamental changes to their fossil fuel-based economies. But like I said, that’s on my cynical days, which, admittedly, are too frequent. At the end of the day, action on black carbon and other SLCPs is a no-brainer, both at home and abroad. We should be doing it—it buys us some time and comes with considerable co-benefits—just as long as it’s not the only thing we do.