Meteorologists and volcanologists have now for a while that volcanoes have a major affect on weather. Not only are they a major contributor to acid rain but can in some cases change climates.

Sometimes volcanoes on destructive plate boundaries throw up huge quantities of volcanic ash. This ash can be propelled into the stratosphere where it may remain for years. Volcanic ash absorbs radiation from the sun which causes cooling to the earth below. Eruptions in high latitudes affect only one hemisphere where as equatorial volcanoes like Krakatoa may cause global cooling.

In the last 100000 years there have been some awesome explosions of volcanoes, dwarfing any modern eruption. The largest eruption took place 75000 years ago which must have blasted dust to over 55 kilometres high! It created a dust veil over the earth which many scientists believe caused an ice age.

All very exciting but wasn't this all a long time a go - well yes and no. There have been no eruptions like that for a while but smaller eruptions which have happened which have changed world climates temporarily. For example in 1815 an eruption of Tambora in Indonesia caused 'a year without summer' which inspired Byron to write his famous poem 'Darkness.'

In fact climate changing eruptions occur every 150-200 years. Perhaps the most significant eruption took place at Krakatoa, Indonesia in the 13th century. The eruptions cause a climate change and it is now the popular view that this triggered the start of the 'Black Death' which wiped out half the population of Europe.

There are other examples of drought, acid rain, cooler climate, storms etc; the risk from volcanoes has not gone away. A mega-explosion could cause a world wide drought or even cause another ice age...

Volcanoes are rarely mentioned in relation to climate change mainly because environmentalists are obsessed with man made causes (which are a problem).  However, I fear volcanoes more than global warming and I think more needs to be done to understand them.