The Oil Drum: Australia/New Zealand | The Bullroarer

20 comments on The Bullroarer - Thursday 17th July 2008

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LeftyfromQueensland on July 20, 2008 - 5:46am

Hmm. Rapidly melting antarctic ice kinda shoots down the theory that ice melting is caused by rising ocean rather than air temperatures, originating from something in the sun or deep in the earth itself - most antarctic ice rests on frozen land, not water.

However, the article also mentions the occurence of several warming and melting events over the past 75 000 years - cleary unrelated to human activity. How can we be certain that this is not just another of the same? That's a fair question isn't it?

I haven't read Gav's links yet, I'll do that before commenting further.

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Cretaceous on July 20, 2008 - 10:52am

Hi again Lefty,

Yes, a very fair question. You're quite right that there have been several Antarctic melting events in the last 75,000 years. However Science has a pretty good handle on explaining the causes.

The main cause of ice-ages is the steady wobbling of the Earth as it spins on its axis, a bit like a wobbling spinning top. The wobble is caused because the Earth's spin is offset by 23 degrees from our plane of orbit around the Sun, and then our Moon has a further orbital offset of 28 degrees from the Earth's plane of rotation as well.
(Did you ever have a Spirograph when you were a kid? http://www.pietro.org/Astro_Util_StaticDemo/MethodsNutationVisualized.htm )

Anyway, the result of this wobbling is a big variation in the amount of solar energy landing on the surface of the Earth at various latitudes. These variations have been named the "Milankovitch Cycles". I'll let you read about them here:
http://en.wikipedia.org/wiki/Milankovitch_cycles

My point in laying out all of this data is to say that because Science can now explain the past history of ice ages, that's why we can be so sure that the current warming is "not just another of the same", as you put it. The West Antarctic ice will melt in the usual unstable way, but the cause of it will be *us* this time, not the wobbling of the planet.

At the moment, the natural Milankovitch cycle should be taking us towards global *cooling*, but in fact this "natural" signal is being completely overwhelmed by the "Greenhouse Effect" of our own emissions. Every year it ticks inexorably up (http://www.esrl.noaa.gov/gmd/ccgg/trends/), and we are probably already well past the "safe" level.
(http://blog.wired.com/wiredscience/2007/12/nasas-james-han.html)

There are further impacts on the planetary temperature from effects acting longer-term than 75,000 years, such as Continental Drift changing the pattern of ocean currents, and the natural balance of CO2 in the air. For instance, most of our oilfields appear to have been originally deposited in hot anoxic ocean conditions during natural runaway greenhouse events. (http://www.abc.net.au/science/crude/resources/)
But once Nature has sequestered enough carbon, things settle down again.

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