Thursday, February 2, 2012

Ice Ages May Be the Result of Shifts in the Polar Axis

At least according to a Harvard scientist and based on computer models.
The idea that slight shifts in Earth's axis might have been enough to trigger the ice ages is a century old.

But a Harvard earth sciences Professor Peter Huybers has finally proved it, using computer models to test competing ideas - and finding that earth's tilting axis is the only one that works.

The finding could have profound implications for our understanding of our planet's climate - and could, its author says, be crucial to 'predicting long-term changes in future climate.'

Two 'cycles' in the way Earth's axis spins have an effect on the cycle - one lasting 10,000 years and one lasting roughly 40,000 years.

When they align correctly, ice melts. At the other extreme, glaciers advance.

The idea that these could dictate the cycles of glaciation in Earth's climate was first proposed by Serbian geophysicist Milutin Milankovitch in the first half of the twentieth century.

'These periods of deglaciation saw massive climate changes,' Huybers said. 'Sea level increased by 130 meters, temperatures rose by about 5 degrees C, and atmospheric CO2 went from 180 to 280 parts per million.'

We ought to understand what caused these massive changes in past climate if we are to predict long-term changes in future climate with any confidence.'

'And at least now we know with greater than 99 percent confidence that shifts in earth's axis are among the factors that contribute to deglaciation.'

When both cycles align 'correctly', the glaciers retreat rapidly.

'When you get that alignment, the radiation that the Northern Hemisphere receives during summer increases by tens of watts per meter squared, and if large Northern ice sheets are present, they tend to disintegrate.'
Of course, so he isn't labeled a heretic:
Huybers emphasises that these cycles are only one factor among many.

'It could also be that orbital forcing causes a rise is atmospheric CO2, and that it’s the increased CO2 that drives the loss of ice sheets,' he said.

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