One aspect of the climate change debate I find particularly troubling is the extent to which CO2 has come to dominate the narrative. By limiting our discussions to CO2 we ignore the topics we can all agree upon. Today I will talk about a topic about which even the most dedicated denialists and the most excitable catastrophists should be able to agree on: black carbon.
Black carbon is the most strongly light-absorbing component of particulate matter (PM), and is formed by the incomplete combustion of fossil fuels, biofuels and biomass. Black carbon is a major component of soot and is the most effective form of PM, by mass, at absorbing solar energy. Black carbon in the atmosphere can absorb a million times more energy than CO2 per unit of mass.
According to recent research, black carbon is the next most important human emission in terms of its climate-forcing after CO2.
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 where microscopic quantities can have pretty significant effects. As described in a paper from Cryosphere, as little as 150 nanograms of black carbon per gram of soot found in sea ice can lead to a decrease in albedo, or solar energy reflected off the Earth's surface, to 70 per cent of its original value. To put that into perspective, 150 nanograms per gram is equivalent to about 2.5 tablespoons of water in an Olympic-sized swimming pool.
By reducing albedo, black carbon causes ice to absorb solar rays instead of reflecting them away. This causes the ice to melt. Once melted, the ice loses even more albedo, allowing the underlying surface (be it soil or water) to further absorb radiation, resulting in even 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. It contributes to the rise in ocean levels and the ensuing risk to coastal communities, and will reduce the availability of fresh water in regions dependent on glacier runoff for their water supplies.
From a human health perspective, a large body of scientific evidence links exposures to fine particles like PM 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. So, even if you have no interest in climate change, you should still want to address black carbon for its human health concerns.
In North America, about half of our black carbon comes from wildfires (over which we have little control) and the other half from diesel emissions (over which we have much more control). By accelerating the cleanup of diesel emissions, we could thus have an effect on climate change while also improving human health outcomes.
According to the EPA, in the developing world mobile sources (19 per cent) and open biomass burning (35 per cent) contribute a smaller portion of the world's inventory of black carbon, while emissions from residential heating and cooking (25 per cent) and industry (19 per cent) have a greater impact. The area that really jumps out is the "domestic/residential" emissions which most people know better as: "cooking fires."
More than 1.3 billion people around the world are without access to electricity and 2.6 billion people are without clean cooking facilities. More than 95 per cent of these people live either in sub-Saharan Africa or developing Asia, and 84 per cent live in rural areas. 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. The World Health Organization estimates that indoor smoke from solid fuels is among the top 10 major risk factors globally, contributing to approximately 2 million deaths annually. Women and children are particularly at risk.
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 previously 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 cooking 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 potentially major forcing agent for climate change, a serious risk to the cryosphere and a human health risk of the first order. By targeting black carbon, the climate warriors on both sides have an option to get out of their mutual trenches and start working together to improve the condition of our planet.
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