Black carbon: The good news or the bad news?

By Paul Andersson
Climate Solutions

So do you want to hear the good news or the bad news?  I will assume you’re like me and want to hear the bad news first.

The bad news is that black carbon (BC)–what makes soot black when it’s escaping from diesel engines, cook stoves, forest fires, airplanes, volcanoes, etc.–has been found to be the second largest contributor to climate change in a comprehensive four year study that was recently released. The study, completed by a multinational team of 31 experts, puts black carbon behind carbon dioxide and just ahead of methane in terms of having the worst heat-trapping effect of all greenhouse pollutants. The report indicates that the direct effects of black carbon are nearly twice what are indicated in the 2007 IPCC’s Fourth Assessment.

Black carbon’s warming effect comes as a double whammy: BC both absorbs heat in the atmosphere and reduces the ability for the snow and ice that it lands on to reflect sunlight back out of the atmosphere. Human health impacts take the seriousness of BC emissions a step further. According to Durwood Zaelke, President of the Institute for Governance & Sustainable Development, who served as a reviewer of the assessment, “Black carbon is not only more important for climate than we thought, it also kills over a million people every year who contract deadly respiratory diseases by breathing air polluted by black carbon. That number could be up to 3.6 million deaths by 2050.”

OK, by now you should be ready for some good news. Unlike carbon dioxide concentrations, which exist and trap heat in the atmosphere for decades, black carbon remains in the atmosphere for only one to four weeks. Its short lifetime also means that its global warming effects are largely regional, benefiting or hurting the areas that act to curtail these emissions, or don’t.  The Center for Climate and Energy Solutions points out that cutting black carbon emissions would immediately reduce the rate of climate change, particularly in the rapidly changing Arctic.The Center goes on to say that technologies to reduce black carbon emissions are available today.

The good news continues, because these “technologies” are indeed being proven, and in a sector near and dear to Climate Solutions: sustainable aviation biofuels. In a recent test flight of a Canadian commercial jet, the first ever blend of 100 percent biofuels was used.The results from the flight, and the fuel used, posted astonishing lifecycle greenhouse gas reductions in the range of 80 percent over fossil fuels for starters. Here’s the rest of the good news from those flight results:

•  a reduction of 50 percent in aerosol emissions,
•  an improvement of 1.5 percent in specific fuel consumption during steady state operations,
•  a significant reduction of up to 25 percent in particles
•  and, up to 49 percent in black carbon emissions compared to the fossil fuel equivalent.
  

The nexus between black carbon, airlines, and Arctic warming has long been debated, with some studies blaming air travel for much of the black carbon that lands on the northern ice cap. A recent study from Stanford atmospheric scientist Marc Jacobson asserts that “the most abundant direct source of black carbon and other climate-relevant pollutants over the Arctic is cross-polar flights by international aviation.” While some may debate that other industries contribute just as much or more black carbon to the Arctic ice sheets, this study focuses on how rerouting flights around the Arctic could help solve the problem.

Jacobson’s study claims that rerouting flights around the arctic could be done at a nominal cost over the decades and have critical impacts on global temperatures. While the study did not look into the temperature-reducing effects of low-carbon aviation biofuels, the results of the Canadian test and the new findings indicate it could be substantial.

Black carbon is a serious climate issue for which climate solutions exist today. Neither flight paths, nor biofuels, nor airplane efficiencies are a panacea. But with better understanding and better technologies, we can more effectively wash away the bad news with the good news.