Soot's global impact on atmospheric warming: NASA researchers found the amount of sunlight absorbed by soot is two-to-four times larger than previously assumed. Reducing sulfates without reducing soot will exacerbate soot's effect because sulfates' high reflectivity index (albedo) counterbalances soot's heat-trapping effect to varying degrees.

..and...

"...The calculated global warming in an 1880-2000 simulation is about one-quarter of observed global warming."

..and..

90 percent of Arctic warming is due to soot causing dirty snow.

A soot particle
Credit: D.M. Smith, Univ. Denver

Links:
Soot contributes 25 percent to global warming (BBC)
NASA: Soot's global impact
NASA: Black soot and snow, a warmer combination