What was done
For the period 1875-2000, the authors "present estimates of past fossil-fuel BC [black carbon] emissions from the United States, United Kingdom, Germany, Soviet Union, India and China," which conglomerate of nations in 1990 accounted for "about 70% and 60%, respectively, of the world consumption of coal and diesel fuel, which are the principal BC-producing fossil-fuels."

What was learned
Qualitatively, in the words of the authors, their results show "rapid [BC] increase in the latter part of the 1800s, ... leveling off in the first half of the 1900s, and ? re-acceleration in the past 50 years as China and India developed."  Quantitatively, they say that climate forcing by BC aerosols -- which is positive and, hence, promotes warming -- "may be of the order of +0.5 W m^-2."  They also note that "estimates of the current anthropogenic BC climate forcing are of the order of 1/3 to 1/2 of the current CO2 forcing."

What it means
These results -- especially the large warming impetus of current BC emissions -- tend to reinforce the sensibility of James Hansen's "alternative scenario" for fighting global warming that we discuss in our Editorial of 17 July 2002, which in a nutshell suggests we should concentrate on trying to halt the growth of old-fashioned air pollution (which is directly responsible for hundreds of thousands of deaths annually and for which there are proven and economical technological fixes) rather than throwing good money after bad in pursuit of unrealistic schemes to reduce anthropogenic CO2 emissions (which are directly responsible for enhancing agricultural and natural ecosystem productivity and for which there are no proven and economical technological fixes).