It was only in 1920 that William J Humphreys, an American climatologist, established a link between Mount Tambora’s eruption and the 'year without Summer'.

Benjamin Franklin had earlier proposed that the cool summer of 1783 was caused by Mount Laki’s eruption in Iceland, but fellow scientists dismissed his submission.

Humphreys explained that the force of Mount Tambora’s eruption propelled ash and gases into the stratosphere (17-50km above the Earth’s surface) where winds blew them across the world over a year. These suspended particles created a dust veil that reflected the sun’s heat.