Soot

Soot, which comes from combustion of many different things, is black so it's a strong absorber. In fact it's second only to CO2 in terms of warming, so it's actually ahead of methane, which you hear a lot about. The interesting thing about soot and aerosols' impact on climate is that their lifetimes are so much shorter. So if we can reduce the soot we can make changes within months versus tens of years. It's not to say we should ignore the CO2 and the greenhouse gases but it could buy us some time while we actually do the right strategies to reduce the greenhouse gases.