Black soot comes from and biofuels such as wood and organic fuel in cooking fires, diesel and fuel oil emissions, wildfires, agricultural burning, etc. The problem is most severe in developing and third world countries. New studies have shown that black carbon is far more significant at warming than previously assumed. It is a major part of the Asian Brown Cloud or ABCs that nearly constantly cloak much of Asia. It combines with other air pollutants like sulfur dioxide and nitrogen oxides (NOx) to form a sort of super smog (ABCs).
Black carbon traps heat on earth a little differently from greenhouse gasses. When the suns energy (light) hits the black carbon the energy turns into heat energy (infrared energy) just like when sunlight hits the Earth. Black carbon also captures heat when sunlight reflects off of the earth and bounces back to hit the black carbon in the atmosphere. The black carbon, in both cases, heats up and transfers it heat to the atmosphere. Greenhouses gases works by capturing that energy from the sun that has already been converted to heat when it hits the Earth’s surface by forming a gaseous "blanket" that prevents the heat from escaping to space.
The new studies show that black carbon is 60% as effective at warming the atmosphere as CO2. This makes it the second most important contributor, behind CO2, in warming the planet.