The frightening origins of glacial cycles


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:  The Bifurcation Structure and Noise Assisted Transitions in the Pleistocene Glacial Cycles

3 Responses to “The frightening origins of glacial cycles”

  1. ZEPHIR says:

    Why not. The more chaotic is the influence of non-anthropogenic phenomena, the more relevant the influence of well predictable anthropogenic factors of global warming becomes from statistical perspective.

  2. John says:

    No, the more unpredictable factors affect climate, the less relevant our known variables become, that’s why it’s scary.

    Also, we have no idea how predictable anthropogenic factors are, or even how relevant.

    So Zephir, you managed to miss the point, be completely wrong and make a totally separate false assumption in one short post. Well done.

  3. ZEPHIR says:

    We know already, human activity can affect the climate even on per week basis, so here’s no experimental evidence against such influence in long-term period. Experiment always goes first.

    We know quite exactly, how much fossil fuels we are burning, how the increase of CO2 concentration should increase the green house effect, and so on.

    Every other arguments concerning the apparent noise in climatic models can be used as an evidence for man made global warming by the same way, like against it. So they will compensate like every noise.