Earth's History: Freeze and Fry

Today’s rapid climate change is undoubtedly the result of greenhouse gases produced by humans. But extraordinary swings in our planet’s past climate have been caused by changes in its interior and influences from deep space.

In the winter of 1780, New York harbour froze over: people walked across the ice from Manhattan to Staten Island. Around the same time, the French invaded the Netherlands over frozen rivers, while - on a lighter note - Londoners held Frost Fairs on the iced-up River Thames (pictured).

This was the period of the Little Ice Age. The world was then about one degree cooler than the average for the twentieth century.

The Solar Connection

Meteorologists aren’t the only people to pick out this period as unusual: they’re joined by astronomers who study sunspots (pictured, below). Today, these dark patches – marking magnetic storms on the Sun - come and go in an 11-year cycle. But there was a complete dearth of dark spots on the Sun from 1645 to 1715, the time that the Earth plunged into the Little Ice Age.

This apparent link between the Sun’s magnetic activity and the Earth’s climate could be coincidence. But German researcher Sami Solanski has confirmed the effect. Based at the Max Planck Institute for Solar System Research, in Katlenburg-Lindau, Solanski has pushed the Sun’s magnetic record back to 9000 BC. No-one was observing sunspots then, of course, but the Sun’s activity shows up in certain isotopes - carbon-14 and beryllium-10 - that are preserved in ancient pieces of wood and deep in the ice of Greenland and Antarctica.

Solanski has found that the Sun’s magnetism and the Earth’s temperature march hand-in-hand over the millennia. When the Sun is violent, our temperatures go up. When the Sun is dormant (as in the Little Ice Age), our temperatures drop. He finds, however, that this correlation stops around 1970, when manmade global warming starts to kick in. Solanski reckons that solar activity can account for only 30%, at best, of the Earth’s warming in the past 40 years.

Volcanic Cool

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.

Recently - in geological terms - the Ice Ages have repeatedly put our planet in the deep-freeze - but what drives them? Read on to find out more....