Mt.

Volcanic Cooling

The increasing concentrations of greenhouse gases in the atmosphere are not the only factors influencing climate. Explosive volcanic eruptions can inject enormous amounts of sulfur dioxide and ash into the atmosphere. Aerosol particles injected into the stratosphere can result in climate changes lasting up to several years. Observed climatic responses to the Mt. Pinatubo eruption have included tropospheric cooling, stratospheric warming, and an overall drop of about 0.5°C in the global average surface temperature.

There are not yet comprehensive estimates of how the effects of changes in aerosol concentrations, changes in land cover and land use, and changes in concentrations of greenhouse gases will combine with natural influences to alter the global climate. Examination of the temperature record of the last 100 years does show a warming of about 0.5°C, only temporarily reversed recently by the volcanic influence of Mt. Pinatubo, suggesting that the enhanced greenhouse effect is exerting the primary influence. The fact that this warming is somewhat less and different in timing than that predicted by computer models emphasizes the need for continuing research directed toward gaining a better understanding of both human and natural influences such as solar variability on the climate system.