Sun's dimmer switch
Could the sun be responsible for the Earth's ice ages
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Thursday, 25, Jan 2007 02:47
A 'dimmer switch' inside the sun causing its temperature to rise and fall could be responsible for the Earth's ice ages, it has been claimed.
Commonly-held views about the sun's temperature state that it is held constant by the opposing pressures of gravity and nuclear fusion.
But a new computer model outlined in the New Scientist magazine and developed by Robert Ehrlich of George Mason University, US, found that there are some long-term variations in its average temperature of 13.6 million Kelvin (an alternative temperature scale used in physics).
These variations oscillate in cycles lasting either 100,000 or 41,000 years - the same frequency as the Earth's ice ages during the last million years.
During ice ages there is a long-term decline in the planet's temperature, causing an expansion of ice sheets and mountain glaciers.
Other scientists have cautioned however that a definite link between the sun's temperature and the Earth's ice ages is not necessarily proved by Dr Ehrlich's computer model.
Instead, most maintain that changes in the Earth's orbit, known as Milankovitch cycles, are most likely to cause the temperature change.
Explaining why he believes the 'dimmer switch' theory may be incorrect, Neil Edwards, a climatologist at the Open University in Milton Keynes, told the New Scientist: "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. I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation."
Dr Ehrlich's future work to assess whether the sun's temperature could affect the Earth will now include studies of red dwarfs - smaller and relatively cooler stars.