Black Carbon is a climate forcing agent. It warms the Earth by absorbing sunlight and heating the atmosphere and by reducing albedo when deposited on snow and ice and indirectly by interaction with clouds.

A major source of black carbon is diesel exhaust. Black carbon is responsible for up to 4O% of net observed global warming. When these particles land on ice caps or glaciers they absorb heat from the sun and cause ice melt. This is a very non-linear accelerant of climate change. 

Because black carbon remains in the atmosphere only for a few weeks, reducing black carbon emissions may be the fastest means of slowing climate change in the near term, and consequently avoiding an approaching tipping point. 

More information on carbon particulates