Sunday, February 04, 2007

Global Warming From an Earth Scientist’s Perspective

Although he is not actually the official nominee, Al Gore most certainly deserves a lot of the credit for production of this thought-provoking documentary, “An Inconvenient Truth”. What a year for Al, nominated for an Oscar (or very nearly so, at least), and a Nobel Peace Prize. His film has been both praised by environmentalists and panned by the corporate world.

Energy companies are constantly bombarding us with denials that greenhouse gasses from hydrocarbon combustion are contributing to a global rise in atmospheric temperature, and that this is causing ice at Earth's poles to melt, producing a global rise in sea level. I thought I would take a minute and let you know why

Oil and gas exploration techniques underwent a revolution in the 1980’s. A whole new subscience evolved called “Sequence Stratigraphy”. Implicit in sequence stratigraphy is the notion that global sea levels have risen and fallen hundreds, no some say thousands of times in geologic history.

I tried to find a Mesozoic-Cenozoic Cycle Chart online to illustrate the point but all I could find was the chart at left that is also posted on Wikipedia.

It’ll do.

According to that chart, and this one, the last sea level lowstand was about 20,000 years ago during the last glacial advance – the so-called “Ice Age”. Water normally in the ocean basins was trapped on the continents in vast thick ice sheets. Sea level has risen since then, and in fact, is still rising.

That’s their claim. Sea level rise and fall is a natural and cyclic thing. What drives it, according to present theory, are Milankovic Cycles, that is, cycles of Earth’s “wobble” on its axis between 21 and 24 degrees relative to the plane of Earth’s orbital path. This cycle is estimated to occur once every 26,000 years. Superimposed on that is a change in Earth’s orbit from elliptical to circular, and back to elliptical. Timing for this cycle is 44,000 years. Other cycles superimpose on this to produce the net changes in sea level as shown on the Hallam and Exxon Curves.

So it’s their claim that sea level changes are natural events and that they are being made patsies in a huge hoax.

As a former earth scientist I can see where they are coming from, but I also think that they are missing the point. Global sea level changes are measured in centimeters per thousand years. Historic changes can be seen in ancient seaports that are now underwater. From where I sit, I wonder whether we are exacerbating the whole thing by altering the gas content of our atmosphere, something that has been documented.

The analogy is being on a boat with a slow leak with no life vest and never taught to swim, all of that exists plus the fact that someone is dumping water into the boat with a Dixie cup.

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