Why ice, man?

World leaders, big business, and scientists alike argue incessantly over global climate predictions, but by definition the northern hemisphere is currently in the throes of an Ice Age with vast areas embedded in permafrost and glaciation. But, the answer to the question why have large areas of the northern hemisphere existed in an ice-locked state for the last 2.7 million years is only now being answered.

Gerald Haug and colleagues at the GeoForschungsZentrum Potsdam (GFZ) and Andrey Ganopolski and his team at the Potsdam Institute for Climate Impact Research (PIK) have a possible solution to this ancient mystery. In order for ice shields to grow, the Polar Regions must be cold enough for rain to turn to snow and at the same time there needs to be enough precipitation for winter snowfalls to exceed the summer thaw. Palaeoclimatic data show that the northern hemisphere has fulfilled both conditions for 14 million years, so why is it only relatively recently that the great glaciation began?

Gerald Haug

The Potsdam team has discovered that dramatic changes in oceanic circulation occurring 2.7 million years ago are to blame. Their climate data and model calculations show that the upper layer of the sub-arctic North Pacific became more stratified leading to larger seasonal differences in the North Pacific sea surface temperatures. The warmer autumnal oceans meant greater evaporation and this coupled with colder winters and springs meant the extra snow did not melt.

Ever since, the northern hemisphere has languished in an Ice Age that has moved in turns from extreme cold to temperate over the millennia.

Why are we locked in an ice age? (Photo by David Bradley)

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