Improved Method to Measure Impact of Volcanic Eruptions on the Climate

An international team of scientists have developed a new, more accurate method to measure and simulate the short-term drop in hemispheric temperature that typically follows a large, volcanic eruption.

Just to recap, large volcanic eruptions can cause temporary (up to a few years), but significant cooling of the surface by ejecting tremendous amounts of sulphur high into the stratosphere. The sulphur then gets converted to aerosols, which block a portion of the sun's rays, resulting in a hemispheric cooling influence.

Increased albedo due to a large volcanic eruption.

In order to quantify the cooling, scientists have used two approaches...dendroclimatology (tree ring proxy analysis) and climate model simulations.

However, these two approaches have unfortunately produced contradictory results. Model simulations have shown significantly greater and longer cooling than the dendroclimatic reconstructions, according to the University of Geneva report.

In order to help solve this problem, a team of dendrochronologists came up with a new reconstruction of the northern hemisphere summer temperature in the last 1,500 years that is based on maximum latewood density, which is very sensitive to temperature variations.

The inclusion of density allowed clear detection of all major eruptions, according to the report. The new results show that the year following a large eruption had greater cooling compared to the previous reconstructions, but that the cooling did not last more than 3 years for the hemisphere.

The second team, which involved climate physicists, used a sophisticated climate model that basically combines more variables than earlier modeling. What they found was that the new climate model simulations showed less disruption in sun ray exchange due to volcanic activity compared to previous climate simulations used by the IPCC.

The crater of Mount Tambora.

This new study brings the results of these two approaches much more in line with each other. Through this new method the team concluded that the eruptions of Samalas (1257) and Tambora (1815) produced an average drop of 0.8 to 1.3 degrees C. in the northern hemisphere during the year following each eruption.

Both approaches now also agree on the average length of this significant cooling following a major eruption. What they found was an average of two to three years of cooling following those eruptions.

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This study is published in the journal Nature Geoscience.

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