O is the most abundant greenhouse gas, but its concentration in the atmosphere varies with temperature. Volcanic Effects Volcanoes produce several things that result in changing atmosphere and atmospheric temperatures. CO 2 produced by volcanoes adds to the greenhouse gases and may result in warming of the atmosphere. Sulfur gases produced by volcanoes reflect low wavelength radiation back into space, and thus result in cooling of the atmosphere. Dust particles injected into the atmosphere by volcanoes reflect low wavelength radiation back into space, and thus can result in cooling of the atmosphere.
Chlorine gases produced by volcanoes can contribute to ozone depletion in the upper atmosphere.
The Mt. Pinatubo eruption in 1991 and El Chichon eruption in 1981 released large quantities of dust and sulfur gases - resulted in short term cooling of atmosphere. Volcanism in the middle Cretaceous produced large quantities of basalt on the seafloor and released large amounts of CO 2 . The middle Cretaceous was much warmer than present, resulting in much higher sea level. Carbon Dioxide in the Atmosphere CO 2 of atmosphere has been increasing since the mid 1800s. Correlates well with burning of fossil fuels.