"Black Carbon Pollution Emerges As Major Player In Global Warming"

From this article:

ScienceDaily (Mar. 24, 2008) — Black carbon, a form of particulate air pollution most often produced from biomass burning, cooking with solid fuels and diesel exhaust, has a warming effect in the atmosphere three to four times greater than prevailing estimates, according to scientists in an upcoming review article in the journal Nature Geoscience.

Scripps Institution of Oceanography at UC San Diego atmospheric scientist V. Ramanathan and University of Iowa chemical engineer Greg Carmichael, said that soot and other forms of black carbon could have as much as 60 percent of the current global warming effect of carbon dioxide, more than that of any greenhouse gas besides CO2.

Two comments:

1. If the science is "settled", how can the estimated sensitivity for this one factor vary by a factor of three or four?

2. If the new estimates are correct, doesn't that lop a large chunk from a "new" modeled sensitivity for carbon dioxide, since we've only got a fixed .6 degrees C. of 20th century warming to work with?