In 1783, the inhabitants of Iceland were treated to the spectacle of a wall of fire spouting from the ground. It was accompanied by the greatest lava outpouring in history, along with lethal gases, such as acidic sulphur dioxide. A quarter of Iceland’s population died. And the following winter, Benjamin Franklin – then in Paris – noted the exceptionally cold conditions, and was astute enough to blame the eruption in Iceland.
The great explosions of the Indonesian volcanoes Tambora in 1815 and Krakatoa in 1883 each lowered Earth’s temperature by more than a degree. But in the geological past, eruptions had an even more dire effect. At the Siberian Traps in Russia, some 250 million years ago, the Earth witnessed its largest ever outpouring of lava – enough to cover the entire planet with three metres of molten rock. The ash and dust first cooled the planet to freezing point; then greenhouse gases heated it up. The toxic gases from the eruption, followed by the freeze/fry cycle, killed 95% of species on Earth.