In 1783, Benjamin Franklin speculated that the eruption of Hecla in Iceland was the cause for a very cold summer[1]. The Royal Society's Krakatau Committee Report contains a 312-page section on the atmospheric effects of the 1883 Krakatau eruption. In 1913, Humphreys[2] stated that the dust in the upper atmosphere would scatter, reflect and absorb the Sun's radiation. Humphreys also pointed out that a large volcanic eruption could upset the atmospheric circulation patterns which could trigger an Ice Age. These historical accounts demonstrates that the climate effect from volcanoes is not a new concert. At present there are three major methods for studying volcanic-climate interactions: historical correlations, remote sensing, and computer modeling.
People study historical eruptions for evidence that large volcanic eruptions cause climate changes[3]. Changes in Earth's climate are compared to the times of major volcanic eruptions to see if a correlation exists. The Earth's climate record is preserved in tree rings, ice cores and written accounts. The time of volcanic eruptions are determined by acid script in ice cores[4], and radio-carbon-dating.
By accessing the impact of historical eruption, it is hoped that you could scale eruption up, to determine the effects of the very large volcanic erruption that exist in the geological record. The scaling of the climate effects of volcanoes with eruption size may not be simple. There may be nonlinear effects involved, such as the self removeral of atmospheric contaminates.
The major of emissions from volcanoes to the atmosphere is in the form of volcanic eruption columns. There are three parts to a eruption column; gas thrust region, convective region, and umbrella region. Above the vent is the gas thrust region, where particles are propelled upwards like being shot from a gun. The gas thrust region is less than about 4 km. The convective region is charaterized by buoyant gases, which carry finer particalls upwards, while larger particalls fall back. Above the convective region is the umbrella region, where the volcanic cloud spreads outward like an umbrella.
The deployment of satellites makes possible the remote sensing of volcanic eruption columns from a global view point. A volcanic cloud emits three main components to the atmosphere: Gases, Particles, and Heat.
Gases that volcanoes emit to the atmosphere[5]:
The Cascades Volcano Observatory has a wonderful discussion on volcanic gases on their Volcanic Gas Page.
Volcanic particles consist of silicates of glass, phenocrystals and aerosols. The amount of time that silicate particles remain in the atmosphere depends mainly on the size of the particle. The larger the particle, the faster gravity will pull the particle to the Earth's surface. Even though a majority of the mass of an eruption falls out within the first few hours, a volcanic ash cloud can be tracked with AVHRR for several days after an eruption[6].
The longest lasting volcanic aerosols are sulfates. Since sulfates are so long lasting, they are believed to be the most important aerosol from a climate view point. Most of the sulfur(SO2 H2S) that is emitted by volcanoes is slowly converted to sulfuric acid (H2SO4). This sulfuric acid affects the Earth's climate by increasing the planetary albedo. With a larger albedo, the amount of solar radiation reflectived back to space increases. This results in a lowing of temperatures. The lower temperature could increase the amount of snow cover, which will further increase the albedo. A very large volcanic eruption could trigger this type of feed back which could lead to the on set of an ice age.
The amount of sulfates that is emitted by a volcano does not just depend on the size of the eruption. Mt St Helens and El Chichon both ejected 0.2-0.5 Km^3 of dense rock. However, El Chichon emiited about 100 times the amount of sulfur dioxide than Mt St Helens. As a result of the large amount of sulfuric acid added to the atmosphere, the El Chichon eruption had a large effect on Earth's climate.
The Total Ozone Mapping Spectrometer (TOMS) instrument was develped to map ozone, however scientist have found it useful in the detection of sulfur dioxide gas (SO2), which is a percurser to sulfate aerosols.
Locally, volcanic eruptions are very hot, but they do not contribute greatly to global heating of the Earth's oceans or atmosphere. A large amount of the heat produced from an eruption goes into the latent heat. Volcanic heat may affect local weather, but this seems to be a short lived, local effect that does not affect Earth's climate.
For a discussion on the modeling of climate effects from the Mt. Pinatubo Eruption see the GISS Institute on Climate and Planets page.
Contains a discussion on volcanic gases.
This page is from the EOS Reference Handbook. It contains information on EOS interdisciplinary science investigation of active volcanism, volcanic hazards, and volcanic inputs to the atmosphere.
Discussion on how future satellites will broaden our understanding of the climate impact of volcanoes.
Check out the Slide Set #1. It contains observation of volcanic aerosols from the Mt Pinatubo Eruption using TOMS, MLS, and SAGE II.
Description of a numerical climate experiments to incorporate the effects of Mt. Pinatube's Volcanic aerosols into a numerical climate model. Such a model is hoped to improve our understanding of the effects of Volcanic aersols on climate.
Observation of volcanic SO2 clouds using TOMS.
Descripts the EOS IDS Volcanology Team investigations.
Describes cooling effects of volcanoes, volcanoes and ozone depletion, and monitoring the effects of volcanoes.