One feature of the climate change debate I find particularly troubling is the extent to which CO2 has come to dominate the narrative. Certainly CO2 is a critical component of the climate change discussion, but there are other important areas of potential advancement that have been essentially ignored in the policy debates and discussions dominated by talk of CO2. One aim of this blog is to form an intersection between climate science and climate policy. My general goal has been to not recommend global policies but to evaluate the information out there and figure out what can actually be accomplished at a regional level. I am going to make an exception in this case as there are some topics upon which even the most dedicated denialists and the most excitable catastrophists should be able to agree; one such topic is that of black carbon. The topic of black carbon has been all but ignored to date in the climate change debate, but the release of a major multi-author paper in June 2013, combined with some very compelling observational data on its effects on Arctic ice and glaciers has brought topic out from under the covers.
Since this topic has received such little play in the past let’s start with a quick definition to help set the stage; this is from the US EPA:
Black carbon (BC) is the most strongly light-absorbing component of particulate matter (PM), and is formed by the incomplete combustion of fossil fuels, biofuels, and biomass. BC is emitted directly into the atmosphere in the form of fine particles (PM2.5). BC is the most effective form of PM, by mass, at absorbing solar energy: per unit of mass in the atmosphere, BC can absorb a million times more energy than carbon dioxide (CO2). BC is a major component of “soot”, a complex light-absorbing mixture that also contains some organic carbon (OC).
In the IPCC reports, black carbon has historically been more of a footnote. It was recognized as an issue to be addressed but was mostly given short shrift. This was due to the nature of the IPCC process and its reliance on older peer-reviewed articles. The 2007 IPCC Working Group I estimate of black carbon forcing was 0.2 +/- 0.15 W m-2. This should change with the publication of Bond et. al 2013 (and I really mean et. al..it has more high profile authors than you can shake a stick at) published in the Journal of Geophysical Research: Atmospheres (abstract full report (big file)). As described in the paper:
We estimate that black carbon, with a total climate forcing of +1.1 W m-2, is the second most important human emission in terms of its climate-forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing.
This new estimate really changes the game with respect to its importance. A particularly troubling aspect of black carbon is its association with decreases in Arctic ice cover and enhancing the retreat of glaciers. Black carbon is produced all over the world but can deposit on ice and snow and microscopic quantities can have pretty significant effects. As described in a paper from Cryosphere: an addition of 8 ng g−1 of black carbon causes a decrease to 98.7% of the original albedo for first-year sea ice compared to a decrease to 99.7% for the albedo of multiyear sea ice, at a wavelength of 500 nm. Thus, instead of the ice reflecting solar rays the black carbon absorbs the radiation. In doing so, the black carbon melts the ice and once melted the ice loses its albedo and the underlying surface (be it soil or water) is able to further absorb radiation resulting in more ice loss. Whether you accept the anthropogenic nature of climate change or not, accelerating glacier retreat and enhanced loss of Arctic and Greenland ice should be a concern as they will contribute to enhancing the rise in ocean levels with ensuing risk to coastal communities and will reduced the availability of fresh water in regions dependent on glacier runoff for their water supplies.
As described above, black carbon seems to be a pretty bad actor in the field of climate change and is damaging to the cryosphere, but it also has another issue that should concern even those people uninterested in these two topics. A large body of scientific evidence links exposures to fine particles (i.e., ambient PM2.5 mass concentrations) to an array of adverse health effects, including premature mortality, increased hospital admissions and emergency department visits for cardiovascular and respiratory diseases, and development of chronic respiratory disease ref. So even if you have no interest in climate change you should still want to address black carbon for its human health concerns.
The next question to ask is: where is this black carbon coming from? Well according to the EPA’s report on black carbon, most U.S. emissions come from mobile sources (52%), especially diesel engines and vehicles. In fact, 93% of all mobile source emissions came from diesels in 2005. The other major source domestically is open biomass burning (including wildfires), although residential heating and industry also contribute.
So the problem in North America is mostly associated with wildfires (over which we have little control) and diesel emissions, (over which we have a lot of control). The US has plans for emission controls for diesel engines but by climate change standards the funds being allocated to enhance the efforts are pretty minimal. Accelerating the cleanup of diesel emissions would have an effect on climate change while also improving human health outcomes. This seems like something we can all get behind. One way would be to direct serious research dollars into finding alternatives to diesel fuel for the movement of heavy trucks and trains. In British Columbia, we have a company called Westport Innovations Inc. that has developed a mechanism to convert diesel engines to use natural gas. Similar efforts should be jump-started to speed up the movement away from diesel as the primary fuel for heavy engines (conflict note: I have absolutely no Westport stock in my portfolio and have no financial interests in the company).
While North American and Northern European emissions of black carbon are due primarily to wildfires and transporting goods, sources in developing countries are substantially different than in the United States: mobile sources (19%) and open biomass burning (35%) represent a smaller portion of the global inventory, while emissions from residential heating and cooking (25%) and industry (19%) are larger. The area that really jumps out is the “domestic/residential” emissions or as reported by the EPA, cooking fires. Those of us lucky enough to live in North America are used to being able to use natural gas, electricity or propane to cook our meals but globally over 1.3 billion people are without access to electricity and 2.6 billion people are without clean cooking facilities. More than 95% of these people are either in sub-Saharan African or developing Asia and 84% are in rural areas (ref). These people are left to cook over open fires or in wood stoves using brush, animal dung and any wood they can get their hands on. From a human health perspective, the World Health Organization estimates that indoor smoke from solid fuels is among the top ten major risk factors globally, contributing to approximately 2 million deaths annually. Women and children are particularly at risk (ref). But human health is not the only concern, all that woody material has to come from somewhere and in sub-Saharan Africa and Southeast Asia that means deforestation. I’ve written elsewhere how important intact forests are for ecological protection but they also have serious implications for helping to mitigate/decrease the rate of climate change. So not only are these families putting their lives at risk just to cook their meals, they are also contributing to deforestation and increased release of CO2. In these countries, enhancing access to electric power grids and alternative energy sources should be an aim that we can all agree upon.
Looking at black carbon we have a major potential forcing agent for climate change; a serious risk to the cryosphere; and a human health risk of the first order. By targeting black carbon I feel we can get out of our mutual trenches and start working together in a way that will improve the condition of the planet. In doing so we can identify those people actually interested in having a perceptible effect on improving the planet and smoke out the rent seekers and hangers on who seek only to extend the debate for their own purposes.