Particulate Consequences of Particular Future Activities
Particulate pollution from vehicles, power plants, industry and wood burning reduces air quality and affects climate. Each of these activities generates its own mix of chemical compounds and the impact of the particles, or aerosols, depends upon their chemistry, size and other characteristics.
Image at right: Incomplete combustion in power plants is an important anthropogenic (human-caused) source of aerosols. (Image: Energy Information Admin., U.S. Dept. of Energy).
The dominant climate impact of aerosol pollution is to scatter radiation back to space and thereby cool the earth"s surface. However, inefficient combustion of wood, coal and diesel tends to produce dark carbonaceous material (black carbon, or soot) that also absorbs radiation and warms the atmosphere. Thus, aerosol pollution can either warm or cool the climate, depending on its chemistry, which in turn depends on the activity responsible for the pollution. As we ponder our future climate, it is helpful to examine how changes in specific activities are likely to alter the production of dark-warming particles and shiny-shielding particles.
In a recent study, we tracked aerosol pollution changes according to two established projections of future activities (IPCC Special Report on Emissions Scenarios projections A1B and B1) for the next 50 years. Both assume rapid economic growth and relatively low population growth. However, the A1B scenario has economically driven technology development while the B1 scenario has greater introduction of cleaner technologies. We divide our aerosols into categories according to whether they were produced by transportation, power generation, industrial activity, domestic burning or open biomass burning. We track each of these types within the global GISS "ModelE" aerosol model.
Figure above: Global maps which show the cooling (purples-blues-green) and warming (yellow-orange-red) tendencies for the present (top row), for the A1B projection in the year 2050 (second row), and for B1 in 2050 (third row). The first column has the net radiative forcing (warming or cooling tendency), and the other columns show the breakdown according to aerosol source. The numbers above each map indicate whether the net effect is warming (positive) or cooling (negative). (Figure also available as large GIF or PDF.) (Image: D. Koch, NASA/GISS, Columbia Univ.)
Aerosols from power and industry sources contain significant sulfate, a scattering aerosol. These aerosols presently come mostly from the major industrialized regions such as North America, Europe and Southeast Asia. These activities thus cover the northern hemisphere with a shiny, cooling sulfate shield (bright purple in the figures). In the cleaner B1 scenario, this pollution and the consequent shield are expected to decline, resulting in a warmer future. For the dirtier A1B scenario these emissions are projected to increase, enhancing the cooling effect. In both scenarios the dominant source regions shift southward, away from the current industrial regions toward developing regions in South Asia, the Middle East, Africa, and South America.
Image at right: Natural and anthropogenic biomass burning, such as forest fires and the burning of fields in the tropics, produce black carbon aerosols, i.e., soot. (Image: NASA).
Biomass burning produces a near-balance of warming and cooling carbonaceous aerosols. The future scenarios project reduced burning in Africa and an overall slightly increased warming effect.
Transport and residential sources produce aerosols that absorb (warm) more than they scatter (cool). Today the residential burning pollution is estimated to be the largest source of absorbing particulates. However our future scenarios project that these emissions will decline, as cleaner methods of domestic heating and cooking are developed. Transportation, especially diesel vehicles, would then become the largest source of absorbing aerosols. Reductions of absorbing aerosol pollution from transportation and residential burning would help to reduce global warming and while also improving air quality.
News Release: NASA Probes the Sources of the World's Tiny Pollutants (Jan. 30, 2007)
News Release: Global 'Sunscreen' Has Likely Thinned, Report NASA Scientists (Mar. 15, 2007)
Koch, D., T.C. Bond, D. Streets, and N. Unger, 2007: Linking future aerosol radiative forcing to shifts in source activities. Geophys. Res. Lett., 34, L05821, doi:10.1029/2006GL028360.
Koch, D., T.C. Bond, D. Streets, N. Unger, and G. van der Werf, 2007: Global impacts of aerosols from particular source regions and sectors. J. Geophys. Res., 112, D02205, doi:10.1029/2005JD007024.