Wednesday, April 16, 2008


The Power of Inference

There are a few men out there who have never had the misfortune of watching competitive ice skating. This first part is for them. There is a move all skaters do during a spin. They bring their arms in close to their bodies and lo! and behold, the rate of spin increases. There is an explanation in physics having to do with angular momentum and center of mass, and a formula here. Perhaps that formula doesn't completely explain it. It's true though. I don't skate much but I did a similar thing once in a science museum in Munich on a rotating chair with 2 Kg dumbbells in each hand. In fact, the rate of spin increased so much as I pulled my arms in that I almost was thrown from the chair. When I put the weights back out, the rate of spin immediately slowed. Kinda cool.

So, is the Earth doing the same thing? That is, has it moved its 'arms' in or out? Has it increased its mass at the equator or at the poles? The rise in the ocean level near the equator caused by global warming climate change would increase the mass at the edge of the rotation, thus slowing down the rate of rotation (like putting the arms out). A growing of the ice caps in Antarctica and in Greenland would increase the mass of the Earth closer to the axis of rotation (like putting the arms in) thus speeding up the rate of rotation of the planet. Has the rate of rotation sped up or slowed in the past few decades?

It turns out we can tell. There are scientists who are keenly interested in how fast the Earth rotates and we have the reliable timing instruments to know exactly how fast it's spinning which they measure each year) and thus know whether it's speeding up or slowing down. (The Earth would always be slowing down gradually just due to entropy, wouldn't it?)

And here is answer to the question. Money quote:

The International Earth Rotation and Reference Systems Service (IERS) provides very precise data that can answer this question. The IERS calculates leap seconds. Just like leap years add days to keep our calendar in sync with the actual amount of time it takes for the Earth to orbit the Sun, leap seconds are used to keep highly accurate atomic clocks in sync with clocks based on the Earth’s rotation. The Earth’s rotation has slowed down. To keep the clocks in sync leap seconds will have to be added at a constant rate. If the Earth’s rotation continues to slow down leap seconds will need to be added at an increasing rate.

The IERS determines the rotation of the Earth. Data only exists from 1972 to the present. From 1972 thru 1998 (26 years) 21 leap seconds were added. From 1999 to the present (9 years) only 1 leap second has been added. This means since 1999 to the present the Earth’s rate of rotation has increased.

There may be other things causing this (unknown changes in geological features; forces we don't recognize or understand; General Zod, etc.). However, the immediate conclusion is that the ice caps are growing, not the depth of the tropical oceans. This conclusion matches the RSS decline in mean global temperature since the second place high* in 1998 very well. I'm buying it, even though the time scale is so minute as to make it unreliable to ascribe greater meaning thereto.

(h/t Icecap)

*The warmer decade according to the corrected but unheralded GISS was in the 1930s.


That's interesting data, but I don't think it shows much. The earth isn't particularly rigid, and in fact is probably best thought of as a giant magma balloon. From the linked paper, I don't see any correction for a change in water mass distribution causing a corresponding change in planetary shape.

This doesn't say that the effect mentioned is impossible, but I'd really like to see a model that includes that information.
Clearly it's conjecture, but the timing is pretty compelling. See ya'
Again, Roger, the 1998 second place figure is for US temperatures, NOT Global temperatures!
My poor grammar, Andy. The RSS is global and so I described it. You are right about the 30s versus the 90s being more local, but I mentioned it in a kind of footnote without noting the switch in venue. Sorry. The link made it pretty clear though. Thanks all for the comments; they seem to have dropped off of late.
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