There is a new interesting paper in Science on January 5 2007 by Meinrat O. Andreae entitled “Aerosols Before Pollution” [subscription required]. The summary of the article states that
“No unpolluted regions remain in today’s atmosphere…..”
The article includes the text,
“Atmospheric aerosols play a large role in human-induced climate change because of their effects on solar radiation transfer and cloud processes. To assess the impact of human perturbations on the atmosphere’s aerosol content, we need to know the prehuman aerosol burden. This is especially important for understanding the cloud-mediated effects of aerosols on climate, because cloud properties respond to aerosols in a nonlinear way and are most sensitive to the addition of particles when the background concentration is very low…
“….prehuman aerosol levels may have been very similar over continents and oceans, ranging from a few tens per cm3 in biogenically inactive regions or seasons to a few hundreds per cm3 under biologically active conditions. This conclusion renders invalid the conventional classification of air masses into maritime and continental according to their aerosol content. It also implies that, before the onset of human-induced pollution, cloud microphysical properties over the continents resembled those over the oceans, whereas nowadays, cloud processes over most of the continents are shaped by the effects of human perturbation.”
The importance of aerosols within the climate system are supported by a wide range of studies including
Matsui, T., H. Masunaga, R.A. Pielke Sr., and W-K. Tao, 2004: Impact of aerosols and atmospheric thermodynamics on cloud properties within the climate system. Geophys. Res. Letts., 31, No. 6, L06109, doi:10.1029/2003GL019287.
Matsui, T., H. Masunaga, S.M. Kreidenweis, R.A. Pielke Sr., W.-K. Tao, M. Chin, and Y.J. Kaufman, 2006: Satellite-based assessment of marine low cloud variability associated with aerosol, atmospheric stability, and the diurnal cycle. J. Geophys. Res., 111, D17204, doi:10.1029/2005JD006097.
The conclusion that the composition of the global atmosphere is significantly altered by the human input of aerosols from industrial and vehicular activity, biomass burning, and landscape degradation should be a wake up call to the policymakers who have concluded that CO2 is the dominant human climate forcing, and if we can just control its atmospheric concentrations, we can effectively “fight climate change”. The Andreae article illustrates the narrowness of such a CO2 centric view.