Aerosols are the tiny particles of liquid or dust suspended in the atmosphere. The most important anthropogenically generated aerosol is sulphate from SO2 (produced from the burning of coal and oil). Naturally produced aerosols result from volcanic eruptions and desert dust and sandstorms. When held in the troposphere, aerosols reflect some of the sun’s radiation and thus have a negative forcing (cooling) effect. Aerosols may have a significant local or regional impact on temperature, but it can lead to hemispheric scale effects on climate patterns.

In contrast to long-lived greenhouse gases, anthropogenic aerosols are very short-lived in the atmosphere, hence their radio active forcing adjusts rapidly to increases or decreases in emissions.

The diagram below illustrates the cooling effect of atmospheric aerosols.