The push toward cleaner air in Beijing before the 2008 Olympic Games was a vivid reminder of the need to control air pollution, not only in Asia but in many regions of the world (
1). There is mounting evidence for particle- and ozone-related health effects (
2,
3). Furthermore, ozone and aerosol particles affect Earth's radiation balance (
4,
5): Many aerosols cool the atmosphere (a negative forcing), whereas ozone and black carbon aerosol have a warming effect (a positive forcing). There is thus a strong motivation for treating air pollution control and climate change in common policy frameworks (
5,
6). However, recent model studies (
7–
9) have shown that changes in pollutant and precursor emissions, atmospheric burden, and radiative forcing are not necessarily proportional. Furthermore, as Shindell
et al. report on page 716 of this issue, current models do not capture many of the complex atmospheric processes involving aerosols and reactive trace gases (
10).
1 Department of Physical Geography and Ecosystem Analysis, Lund University, 22362 Lund, Sweden.
2 Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
3 NASA Goddard Institute for Space Studies, Center for Climate Systems Research, Columbia University, New York, NY 10025, USA.
4 Max Planck Institute for Chemistry, Biogeochemistry Department, 55020 Mainz, Germany.