Saturday, April 23, 2005

Ice sheets and nonlinear resonance

Antartic glaciers retreating
Analysis of more than 2,000 aerial photographs dating from 1940 and more than 100 satellite images from the 1960s by Researchers from the British Antarctic Survey and the US Geological Survey show glaciers along the Antarctic Peninsula retreating at an increasingly rapid pace and almost 90 per cent have melted significantly in the past 50 years.

It is unclear, however, whether the increased temperature causing the shrinkage is a natural regional effect or a result of global warming, said the scientists who conducted the study, published this week in the journal Science reports ABCnews.

Some of the electrical engineers out in industry are working on an interesting problem. They're trying to reverse the effects of aging on neurons. You see, everyone knows that your vision and hearing decays with age. What they don't realize is that your proprioception also decays. That is, with age you lose your ability to figure out where your body parts are. Close your eyes, extend your arms, and close them at your elbows until your index finger's touch. Your ability to do that without seeing your arms move is due to your proprioception. As you get older, you won't be able to do that as well.

This is also why we fall as we get older. In order to maintain balance, there is a complex control system that causes us to rock back and forth to receive feedback that our balance systems can respond to to keep us upright. If you've ever ridden on a Segway (or one of those wheelchairs that can go up stairs on two wheels) you've noticed that it rocks back and forth constantly. It's a gentle sway, and it's necessary to maintain that equilibrium (which is an "unstable node"). Our bodies do something similar. Trouble is, the "amount" of rocking until those neurons fire increases with age. Our natural balance systems need to rock more to keep us upright, and so sometimes when we need them for balance, they don't kick in soon enough.

So engineers are working on insoles that can be inserted into shoes that excite the neurons on the bottom of the feet with white noise (in other words, noise that is uncorrelated in time). They cannot use any periodic signal or the neurons will be accustomed to it (this is why you don't notice your clothes throughout the day; it's an attentional control system). Turns out that the white noise is a sort of nonlinear "bias" that puts the nerves into a region where they trigger more quickly. People with these insoles inserted (which vibrate too delicately for people to notice) do not sway as much to keep balance.

Now, getting back to climate, this work was actually inspired by studys of CLIMATE CHANGES over time. You see, we get ice ages every 100,000 years or so. Why? Well, the earth as it rotates around the sun also wobbles like a top. This precession is exactly the reason why the Zodiac signs do not fall on the actual zodiac plane today. (sorry astrologers. Try looking in the sky rather than looking in the newspaper) It turns out that the period of this wobble correlates with these particular kinds of ice ages. The trouble is that the wobble does not cause enough of a temperature change to justify the planet covering over with ice.

So you see, the answer was in the random fluctuations in our natural atmosphere. Those fluctuations are like the white noise that "bias" the atmosphere into an ultra-sensitive state. The atmosphere is just ready to trip. It only takes a SMALL TEMPERATURE CHANGE to flip it.

So this is what we like to call "nonlinear resonance." I know, most of you think of "resonance" having something to do with sine waves. That's "linear resonance." This is a more general form of resonance where a small perturbation is made very large simply due to the noisy bias.

My point is, the environment is so very delicate. We don't know what sort of "nonlinear modes" we're going to excite. We don't know where the equilibrium points are, and we don't understand their attractivity and stability properties. Articles like the one I posted above should really concern people.

And yet the Dennis Miller's of the world continue to tell old jokes everyone's heard before about global temperature rising being just like moving to Phoenix -- a small adjustment easily fixed by an A/C unit. These are the same people who have large families who hopefully will grow up to disown their parents for being wastes of breath.

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