The great dry fog of 1783

A persistent dry haze hung over Europe during the second half of 1783. Spawned by the Laki basalt fissure eruption in southern Iceland, this fog evoked much contemporary written commentary, from which the course of events is here reconstructed in a quantitative way. It was the densest European dry fog since the late Middle Ages, and it lay primarily in the troposphere. Spreading broadly toward the south and east, it nevertheless remained mostly confined to the North Atlantic, western Eurasia, and the Arctic. Previously it was believed by many to have risen to the middle stratosphere and to have blanketed much of North America. Composed of sulfuric-acid aerosols, its total mass reached about 200 megatons, as determined from its observed optical thickness. Several authors have pointed out that it may have been responsible for the cold winter of 1783-84, which caused much economic and social distress in many parts of the Northern Hemisphere. As the earliest dry fog to be studied scientifically, it remains the paradigm even today and poses an interesting challenge to climate modelers.