What was done
The authors assessed the effects of atmospheric aerosols around the globe on cloud microphysics via data on aerosol concentration and cloud droplet radii obtained from the polarization and directionality of the earth reflectances (POLDER) instrument on the Advanced Earth-Observing Satellite (ADEOS), which began operation on 30 October 1996 and concluded on 30 June 1997.

What was learned
The results of this study, in the words of the authors, "clearly demonstrate a significant impact of aerosols on cloud microphysics."  Specifically, as aerosol concentrations increased, cloud droplet radii decreased, which phenomenon should have produced a cooling influence due to the greater albedo generally associated with smaller cloud droplets.  They also determined that "the bulk of the aerosol load originates from slash-and-burn agriculture practices and from highly polluted areas," such that "a large fraction of the observed aerosol effect on clouds is probably of anthropogenic origin."

What it means
Although the authors were not able to quantify the degree of cooling provided by the presence of the aerosols they studied, they nevertheless demonstrated that this anthropogenic counterforce to the warming impetus provided by the ongoing rise in the air's CO2 content "is significant and occurs on a global scale."