Radiative forcing quantifies the change in the balance between incoming and outgoing radiation at the top of the atmosphere caused by a given factor; over the last two centuries of industrialization, anthropogenic aerosols (fine particulate matter from fossil fuel combustion, biomass burning, and other sources) have exerted the largest negative (cooling) radiative forcing, by scattering incoming solar radiation back to space and by modifying cloud properties (increasing cloud reflectivity and lifetime), partially offsetting the positive (warming) forcing from greenhouse gases.