Volcanic pollution and climate: The 1783 Laki eruption

The global temperature rise of 0.4°C in the past century is now generally attributed to the greenhouse effect, i.e., the increase of atmospheric carbon dioxide through manmade pollution. Superimposed on this general warming trend are sharp temporary cooling events, usually 1 to 3 years in duration, that coincide with large volcanic eruptions. These events mark a massive natural pollution of the stratosphere, resulting in backscattering of solar radiation and cooling of the earth [ Hansen et al. , 1981]. The latest of these events was the 1963 eruption of Agung volcano on Bali Island that resulted in 0.2°C global cooling, whereas paradoxically the Mount St. Helens eruption in 1980 had no detectable effect [ Robock , 1981], although of comparable magnitude. On the other hand, one of the most severe volcano‐related climate effects in historical times was associated with a largely nonexplosive eruption that produced mostly lava and volcanic gases but little volcanic ash: the 1783 eruption of the Laki crater‐row in Iceland [ Thorarinsson , 1979]. Thus, although volcanism clearly affects climate, it appears that this effect is not simply related to the magnitude or the explosivity of the eruption, i.e., the production of volcanic ash, but rather to some other properties of the magma.