[2015] Volcanic eruptions have a long lasting influence on North Atlantic climate

Particles emitted during major volcanic eruptions cool the atmosphere by reflecting the sun radiations. These volcanic particles have a short term direct effect in the atmosphere. Still, they modify during more than 20 years the oceanic circulation in the Northern Atlantic and modulate European climate.

Multi-decadal oscillations of surface temperature occur in North Atlantic that influence the European climate. This slow variability is due to modifications of the oceanic circulation linking surface and deep currents and bringing heat from the tropics to polar sea around Norway and Greenland. However, the cause for these modifications is still unknown.

In this study, paleoclimatic data have been extracted over the last millennium such as the isotopic composition of water in Greenland ice core enabling estimate of the past temperature variability. These data have revealed a strong link between Atlantic surface sea temperature and Greenland air temperature with an associated periodicity of 20 years. Using numeric simulations from 20 different climate models, it has been shown that major volcanic eruptions such as Agung (Indonesia, 1963), Pinatubo (Philippines, 1991) can modify the oceanic circulation in Northern Atlantic. Indeed, large quantity of particles emitted by the volcanic eruptions toward the high atmosphere reflect part of the solar radiance leading to a cooling at the Earth surface. This coiling lasts only 2-3 years but leads to a reorganization of the Northern Atlantic ocean 15 years after the beginning of the eruption, this circulation accelerates. A slow-down follows 25 years after the eruption before an acceleration 10 years after. The volcanic eruptions are thus playing the role of a pace-maker for the ocean variability at the 20 years timescale.

This result has been confirmed using oceanic salinity, a key factor for the sinking of oceanic water and hence oceanic circulation. They have observed similar variations in the beginning of the 70’s and of the 90’s linked to eruption of the Agung in both numerical simulations and modern oceanic observations. Using both Greenland ice core data and islandic bivalve shells older than 500 years as well as a climate simulation of the last millennium, an acceleration of the oceanic circulation has been observed 15 years after 5 volcanic eruptions that occurred several centuries ago.

Finally, interferences have been highlighted between the last 3 major volcanic eruptions (Agung, 1963; El Chichon, 1982; Pinatubo, 1991) explaining for the first time the recent variability of the north Atlantic ocean. They conclude that a future major eruption could have an influence during several tenths of years on the North Atlantic ocean circulation and hence on our capacity to predict European climate.

Reference: Swingedouw, D., Ortega, P., Mignot, J., Guilyardi, E., Masson-Delmotte, V., Butler, P.G., Khodri, M., and Seferian, R. (2015). Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions. Nat. Commun. 6, 6545.

Press release : http://www.insu.cnrs.fr/node/5230