Over the past several years, global warming has become a highly contentious political issue.  On the left, commentators point to studies linking global warming with the increased burning of fossil fuels by humans.  As might be expected, they favor a transnational, big government solution that would restrict how much carbon each country in the world could pump into the atmosphere each year.  Conservatives, on the other hand, argue that global warming is more the result of fluctuations in the sun's energy output and other factors unrelated to human activity.

  Lending credence to the conservative position is scientific evidence showing that global warming has occurred periodically throughout the Earth's history, long before humans existed.  Unfortunately, this same evidence points to global warming as the primary cause of four of the five great mass extinctions that have ravaged life on Earth.  These extinctions occurred 443 million years ago, 374 million years ago, 251 million years ago (the biggest of them all), 201 million years ago and 65 million years ago.

The most recent extinction, of course, is the one that killed off the dinosaurs.  There is strong evidence that the culprit in that case was a large asteroid that struck the Yucatan peninsula, causing a global catastrophe.  But there is no definitive proof that asteroid impacts caused the earlier extinctions.  In fact, the fossil record seems to show that the earlier extinctions occurred over the course of several thousand years rather than overnight.

  According to Peter Ward, a biology professor at the University of Washigton, it appears that large numbers of marine and land species are periodically asphyxiated by tremendous quanties of hydrogen sulfide gas produced by bacteria that thrive in low-oxygen environments.  Writing in the October issue of Scientific American, Ward lays out the following scenario:

          -- Large amounts of carbon dioxide and methane are released into the atmosphere, probably from volcanos;

          -- Global warming occurs;

          -- The ocean heats up, which makes it less capable of absorbing oxygen;

          -- As a result, hydrogen sulfide produced by anaerobic bacteria near the ocean floor rises to the surface, killing sea life as well as animals and plants on the surface;

          -- The hydrogen sulfide also rises into the troposphere and degrades the ozone layer, allowing ultraviolet radiation to kill more life.

Believe it or not, the current levels of carbon dioxide in the atmosphere are low by geologic standards.  But they are increasing.  In a century or two, the levels may be sufficient to set in motion another mass extinction.

So there you have it.  If massive storms, crop failures and rising ocean levels don't get us, poisoned air will.  Whether we're responsible for global warming or not is beside the point.  We need to find a way of dealing with this threat, or else.

Interesting Factoid:  Hydrogen sulfide is a key component of farts.  The gas contains sulphur, which is why farts tend to stink.  No wonder all those plants and animals dropped dead.