Air Pollution as a Climate Forcing: A Workshop
Day 2 Presentations
Controlling Current and Future Diesel Emissions and Other Sources of Fossil-fuel Particulate Black Carbon and Organic Matter as an Effective Method of Slowing Global Warming
Mark Z. Jacobson
Department of Civil and Environmental Engineering, Stanford University, Stanford, CA
Under the 1997 Kyoto Protocol, no control of black carbon (BC) was considered. Here, it is found, through simulations in which twelve identifiable effects of aerosol-particles on climate are treated, that any emission reduction of fossil-fuel (f.f.) particulate BC plus associated organic matter (OM) may slow global warming more than may any emission reduction of CO2 or CH4 for a specific period. When all f.f. BC+OM and anthropogenic CO2 and CH4 emissions are eliminated together, the period is 25-100 years. It is also estimated that historical net global warming can be attributed roughly to greenhouse-gas plus f.f. BC+OM warming minus substantial cooling by other particles. Eliminating all f.f. BC+OM could eliminate >40% of net warming (>15% of total warming before cooling is subtracted out) within 3-5 years if no other change occurred. Reducing CO2 emissions by a third would have the same effect, but after 50-200 years. Finally, diesel cars emitting continuously under the most recent U.S. and E.U. particulate standards (0.08 g/mi; 0.05 g/km) may warm climate per distance driven over the next 100+ years more than equivalent gasoline cars; thus, fuel- and carbon-tax laws that favor diesel appear to promote global warming. Toughening vehicle particulate emission standards by a factor of eight (0.01 g/mi; 0.006 g/km) does not change this conclusion, although it shortens the period over which diesel cars warm to 13 to 54 years. Although control of BC+OM can slow warming, control of greenhouse gases is necessary to stop warming. Reducing BC+OM will not only slow global warming but also improve human health. A paper describing this work can be found at http://www.stanford.edu/group/efmh/fossil/fossil.html.