Between 1998 and 2014, scientists noted a marked decrease in the rate at which the average temperature was increasing. Originally, this period was attributed to an increase in the heat being absorbed by the deep oceans and weak solar activity. Recently, scientists have determined that up to one-third of this hiatus of warming can be attributed to volcanic activity and aerosols. Volcanoes release aerosol particles that collect above the rain clouds in between the stratosphere and troposphere layers of the atmosphere. These lead to an increase in the albedo of the earth, leading to an estimated .05 to .12 degree Celsius decrease in the average temperature. This is particularly noticeable in the polar regions, where the stratosphere extends as low as six miles above the earths surface. Typically this area is discounted when scientists are testing for aerosols due to volcanic activity because the cloud cover interferes with the measurements.

Because of this decrease in temperature, scientists are speculating that the models used to inform senators and congressmen about policy decisions are actually incorrect. It is wholly possible that the atmosphere is significantly more delicate and responsive to carbon dioxide emissions than is currently believed, and should the models be updated to account for this finding, climate policy could change again in the near future.

Source: http://www.dailymail.co.uk/sciencetech/article-2906874/Volcanoes-cooling-Earth-Aerosols-small-eruptions-reduced-global-temperatures-tropical-rainfall.html