They did know that methane from agriculture and animal husbandry is next in line after carbon dioxide as a gaseous pollutant driving global warming. It's on the Kyoto hit list. Now Dr. Jacobson's simulations show that the atmosphere's average load of sooty particles have more warming power than the air's methane. However, as Meinrat Andreae with the Max Planck Institute for Chemistry in Mainz, Germany, points out in a commentary accompanying Jacobson's paper, particles are not gases. Carbon dioxide and methane linger in the atmosphere for decades.
Particles wash out in a week.
Curbing short-lived soot would bring an instant climate benefit. Moreover, pollution-control authorities are increasingly concerned about soot as a health hazard. It should be easier politically to justify the cost of curbing soot emissions from diesel engines and dirty smoke stacks than to persuade reluctant governments to cut back on carbon dioxide. But, as both Jacobson and Dr. Andreae noted, scientists first have to identify where the soot is coming from. Some comes from diesel engines.