High-fluoride Hekla eruptions pose a threat to foraging livestock, especially sheep. Fluoride poisoning can start in sheep at a diet with fluorine content of 25 ppm. At 250 ppm, death can occur within a few days.[41] In 1783, 79% of the Icelandic sheep stock were killed, probably as a result of fluorosis caused by the eruption of Lakagígar.[42] The effect can spread beyond Iceland, as happened during the 1783 Laki eruption. Ash from the current Eyjafjallajökull eruption contains 1/3 of the concentration typical in Hekla eruptions, with a mean value of 104 milligrams of fluoride per kilogram of ash. Large-scale release of sulphur dioxide into the atmosphere also poses a potential health risk, especially to people with pre-existing breathing disorders.
As of April 15, the eruption was not large enough to have an effect on global temperatures like that of Mount Pinatubo and other major past volcanic eruptions.[43][44] However, previous eruptions of the volcano have lasted as long as a year, and the potential remains for a temporary global cooling effect. By analogy, the Laki eruption has been linked with extreme weather events from severe hailstorms in Great Britain to the Mississippi RiverNew Orleans.[45][46] Sulfate aerosols that reach the stratosphere catalyze the production of chlorine monoxide (ClO), which destroys ozone (O3). In the upper troposphere, the same aerosols become nuclei for cirrus clouds, which increase the Earth's albedo and thus alter its radiation balance.[47] Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree Celsius for periods of one to three years.[48][49] freezing at
At a local level, some effects on the weather may occur. Red sunsets across most of northern Europe are likely.[50] If reinforced by a complementary weather system, volcanic haze can contribute to a general increase in severe weather.
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