Black Carbon: The Dark Horse of Climate Change Drivers

Abstract

For decades, efforts to slow global warming have mostly aimed to limit heat-trapping emissions of carbon dioxide (CO2). Now scientists are pointing to a different class of warming agents they say also must be targeted to keep global temperatures in check. Dubbed “short-lived climate forcings” (SLCFs), these other emissions—namely, black carbon particles, methane, hydrofluorocarbons, and tropospheric ozone—are even more powerful than CO2 in terms of their warming potential. But they persist in the atmosphere for much shorter durations than CO2, which can linger airborne for hundreds to thousands of years.1 Steve Seidel, vice president for policy analysis at the Pew Center on Global Climate Change, says the recent emphasis on SLCFs represents new policy thinking on climate change. “We thought the Kyoto Protocol and its follow-on agreements would get us to where we need to be, but that’s not working out the way we hoped it would,” he says. “So, we’re broadening the discussion and opening up new pathways for going forward.” Given the enormity of human emissions, many climate scientists believe CO2 will one day become the dominant force behind climate change. But for now, CO2 and the SLCFs are nearly on par in terms of their climate changing effects, according to Veerabhadran Ramanathan, a professor at The Scripps Institute of Oceanography. In a report published in February 2011, the United Nations Environment Programme (UNEP) called attention to SLCFs, claiming their emissions must be cut together with CO2 in order to prevent global temperatures from crossing a dangerous threshold.2 Doing that would offer health benefits too, UNEP stated, because SLFCs are also toxic air pollutants. Particulate emissions from diesel exhaust—a major source of black carbon—have been linked to lung and heart disease as well as cancer.3 But where it would take a transformation of the energy sector (at a cost of trillions of dollars over multiple decades1) to drop CO2 emissions enough to influence the climate, cutting SLCFs to achieve a similar goal could be achieved with current technologies under policy frameworks that are already in place, such as clean air regulations, according to Seidel.