In testimony for the US Environmental Protection Agency (EPA) public hearing (earlier post) on the proposed endangerment finding for greenhouse gas emissions under the Clean Air Act (earlier post), Stanford Professor Mark Jacobson urged the EPA to include black carbon in the finding.
Black carbon—soot—is a global-warming agent the immediate control of which will slow the demise of Arctic sea ice faster than will control of any other global-warming agent, Jacobson said. Jacobson first showed in 2000 that black carbon was the second-leading cause of global warming after carbon dioxide in terms of radiative forcing and, in 2002, that its control was the most effective method of slowing warming. In 2007, Jacobson and four colleagues testified in the House Committee on Oversight and Government Reform on the role of black carbon. (Earlier post.)
A recent paper by a pair of researchers from the NASA Goddard Institute for Space (GISS) and Columbia University also found that black carbon is responsible for 50% of the total 1.9 °C increased Arctic warming from 1890 to 2007. (Earlier post.)
Although black carbon from motor vehicles is already regulated under vehicle PM emission rules due to known PM health effects, such regulations still permit substantial BC emissions, and the climate effects of such emissions are significant. Specifically, regardless of the time period, each gram of black carbon in the air warms the air over 300,000 times more than does each gram of CO2. Because eliminating BC emissions almost immediately removes atmospheric BC whereas eliminating CO2 emissions removes atmospheric CO2 over only many decades, eliminating BC can immediately slow down the loss of Arctic ice, whereas eliminating GHG emissions can slow loss only over a longer period. However, both BC and GHG controls are needed.
To date, fossil-fuel plus biofuel soot has caused about 12.5-15% of gross global warming (warming before non-soot cooling particles have been subtracted) or 28-40% of net observed warming (net warming less cooling by non-soot particles). Thus, reducing soot in isolation could eliminate one-third of net warming to date. Whereas, the US emits approximately 21% of the world’s anthropogenic CO2, it emits approximately 6.1% of its soot. However, the warming due to US soot exceeds that due to US methane or nitrous oxide, both of which are included in the endangerment portfolio.
Clearly, soot should be included in this portfolio, since its control is the most effective method of reducing Arctic ice loss. Immediate GHG control is still absolutely necessary to stem short and long-term climate damage. Further, controlling soot will significantly reduce particulate air pollution deaths. Controlling GHGs will also reduce such deaths, as discussed next.—Mark Jacobson
Jacobson went on to describe two of his recent studies. The first found that globally-emitted CO2 increases US air pollution deaths by about 1,000 each year per 1.8 °F, with about 40% due to ozone. “These additional deaths are occurring today,” he said. The second study found that local CO2 emissions produce CO2 domes over cities, which increase local ozone and PM, increasing local mortality.
The study found that CO2 domes increase air pollution deaths by 50-100 per year in California, with most occurring in Los Angeles. As such, reducing locally-emitted CO2 reduces local air pollution deaths even if CO2 in adjacent regions is not controlled. This result contradicts the basis for all air pollution regulation worldwide, none of which considers controlling local CO2 based on its local health impact.—Mark Jacobson
Mark Z. Jacobson (2008) On the causal link between carbon dioxide and air pollution mortality. Geophysical Research Letters, Vol. 35, L03809, doi: 10.1029/2007GL031101
Mark Z. Jacobson. The enhancement of local air pollution by urban CO2 domes.