What makes the Earth pass through Ice Ages?
Robert Ehrlich of George Mason University in Fairfax, Virginia thinks that the sun havs cycles of rise and fall on timescales of around 100,000 years. He made a computer model depicting how temperature fluctuates in the sun's interior.
Standard says the temperature of the sun's interior is maintained constant by gravity and nuclear fusion.
Ehrlich made his suppositions based on the fact that slight variations should be possible on the research of Attila Grandpierre of the Konkoly Observatory of the Hungarian Academy of Sciences, which in 2005 found that magnetic fields in the sun's core could generate small instabilities in the solar plasma, correlated to local oscillations in temperature.
The computer model reveals that some oscillations could enhance one another, turning into long-lived temperature variations. The sun's
interior temperature would oscillate around its medium temperature of 13.6 million kelvin in cycles of 100,000 or 41,000 years.
These timescales coincide with Earth's glaciations: in the past two million years, ice ages have installed approximately each 100,000 years and before their rhythm was at each 41,000 years.
The most accepted idea is that the glaciations are provoked by subtle changes in the Earth's orbit, named the Milankovitch cycles: Earth's orbit gradually shifts pattern from a circle to a slight ellipse and back again roughly every 100,000 years, changing the amount of sun heat the Earth receives.
But Milankovitch cycles cannot explain why the glaciations shifted frequency a million years ago. "In Milankovitch, there is certainly no good idea why the frequency should change from one to another," says Neil Edwards, a climatologist at the Open University in Milton Keynes, UK.
And the temperature shifts provoked by Milankovitch cycles seem not to be big enough to induce glaciations; they should be enforced by feedback mechanisms on Earth, like an alteration of carbon dioxide circuit made by the ice, the weakening of the greenhouse effect. "If you add their effects together, there is more than enough feedback to make Milankovitch work," he says. "Milankovitch cycles give us ice ages roughly when we observe them to happen. We can calculate where we are in the cycle and compare it with observation," he says. "I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation."
Ehrlich agrees that his theory is hard to prove, as variation over 41,000 to 100,000 years is too slow to be studied. "If there is a way to test this theory on the sun, I can't think of one that is practical," he said. There would be one way: red dwarfs, much smaller stars than the sun and consequently with short enough oscillation periods to be watched.
Image credit: NASA