25 January, 2007

Milankovitch goes solar?

From New Scientist:

Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect of temperature fluctuations in the sun's interior. According to the standard view, the temperature of the sun's core is held constant by the opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that slight variations should be possible [due to instabilities caused by interactions with the Sun’s magnetic field]…

…Ehrlich's model shows that whilst most of these oscillations cancel each other out, some reinforce one another and become long-lived temperature variations. The favoured frequencies allow the sun's core temperature to oscillate around its average temperature of 13.6 million kelvin in cycles lasting either 100,000 or 41,000 years. Ehrlich says that random interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other.

These two timescales are instantly recognisable to anyone familiar with Earth's ice ages: for the past million years, ice ages have occurred roughly every 100,000 years. Before that, they occurred roughly every 41,000 years.

The paper is up on arXiv, and his model also has an oscillation in the 22,000 year range as well. This strikes me as a mighty big coincidence; it’s not like we’ve pulled the frequencies of variations in the Earth’s orbit - the Milankovitch cycles generally held to control long-term climate fluctuations - out of thin air. One thing I’d really like to know how sensitive the periods of these solar oscillations, if they exist, are to changes in the temperature structure of the sun, which I suspect we haven’t constrained with absolute precision. That said, a solar oscillation in the 100,000 year range might solve the problem of why it’s such a dominant signal in the climate record.

Anyone care to guess how long it will take for someone to claim this somehow has a bearing on the reality of anthropogenic climate change?

Update: Those of you who don't see the disconnect should head over to Open Mind for a clear explanation of why we think that the current short-term warning we're all worried about cannot be attributed to solar variability)


Brian said...

This paper sounds interesting for sure...

The solar forcing argument is the non-anthropogenic global warming proponent's most used tool in their toolbox. But, these time scales are still way longer than what they usually argue...it really doesn't change much from that point of view.

But, I would agree with you...it will be referred to very soon as "see, it's the Sun! I told you!"

thanks for the link

CJR said...

Search for "ehrlich solar" on Google blogsearch, and you'll see it's already started.

It's annoying that we'll get distracted from debating the actual merits of this idea by such things...