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Global Cooling and Volcanoes | John Seach
Large volcanic eruptions create global cooling by injecting ash into the atmosphere which blocks out sunlight.
Tambora volcano in Indonesia erupted in 1815 are reduced global temperatures by up to 3 deg C.
Pinatubo volcano in Philippines erupted in 1991 reducing global temperatures by 0.5 deg C.
Ice cores from both the Arctic and Antarctic record a massive volcanic eruption in around AD 1258 which would have had global effects.