Climatologists have known for some time that the Earth’s motion around the Sun is not as regular as it might first appear. The orbit is subject to a number of periodic effects such as the precession of the Earth’s axis which varies over periods of 19, 22 and 24 thousand years, its axial tilt which varies over a period of 41,000 years and various other effects.
The combined effect of these variations are often cited to explain the 41,000 and 100,000 year glacial cycles the Earth appears to have gone through in the past.
But there is a problem with this idea: the change in the amount of sunlight that these variations cause is not enough to trigger glaciation. So some kind of non-linear effect must amplify the effects to cause widespread cooling.
That’s not so surprising given that we know that our climate appears to be influenced by all kinds of non-linear factors. Even still, nobody has been able to explain what kind of processes can account for the difference.
Now Peter Ditlevsen at the University of Copenhagen in Denmark thinks he knows what might have been going on. He says that the change in the amount of sunlight the Earth receives acts as a kind of forcing mechanism in a climatic resonant effect. The resulting system is not entirely stable but undergoes bifurcations in which the cycle switches from a period of 41,000 years to 100,000 years and back again, just as it seems to have done in Earth’s past.
“This makes the ice ages fundamentally unpredictable,” says Ditlevsen.
Quite, but the real worry is this: if bifurcations like this have happened in the past, then they will probably occur in the future. The trouble is that our current climate models are too primituve to allow for this kind of bifurcation and that means their predictions could be even more wildly innacurate than we know they already are .
Kinda frightening, don’t you think?
Ref: arxiv.org/abs/0902.1641: The Bifurcation Structure and Noise Assisted Transitions in the Pleistocene Glacial Cycles