Explain how incomplete combustion can cause global dimming.

Incomplete combustion produces C in the form of soot which prevents light reaching the earth.

An incomplete combustion reaction produces CO and C and water vapors instead of CO2 produced in complete combustion. The products of the incomplete combustion are microscopic particles - liquid and solid. They are suspended in the atmosphere. As their amount in the atmosphere increases, the amount of sunlight, reaching the surface of the Earth decreases. This effect is called global dimming.

The particulates that are produced during incomplete combustion enter the atmosphere where they can cause an effect that is known as global dimming. Global dimming is the gradual reduction of sunlight reaching the earth's surface due to particulates in the atmosphere from human activity.