Quantifying the impact of volcanic eruptions on climate

Large volcanic eruptions inject considerable amounts of sulphur in the stratosphere which, once converted into aerosols, block sun rays and tend to cool the surface of the Earth down for several years. An international team of researchers has just developed a method to accurately measure and simulate the induced drop in temperature. Considered the most important volcanic event of the 20th century, the eruption of Mount Pinatubo (June 1991) injected 20 million tons of sulphur dioxide in the stratosphere and provoked a global cooling of 0.4°C on average. To quantify the temporary cooling induced by the largest eruptions over the last 1500 years, whose magnitude exceeded Mount Pinatubo's, scientists usually adopt two approaches : dendroclimatology which relies on the analysis of tree-ring based proxies and climate model simulations in response to the volcanic particles effect. But until now these two approaches delivered results that were quite contradictory, and this prevented scientists from accurately assessing the impact of major volcanic eruptions on climate. Simulations showed greater (between two and four times higher) and longer cooling than dendroclimatic reconstructions. This gap even led some geophysicists to doubt the capacity of tree-ring based proxies to measure the impact of past major volcanic events on climate and to question the models' ability in simulating precisely the climate response to strong volcanic forcings. Reconciliation of observational proxy and model evidence