PBS is at it again. The other night they ran another breathless science documentary called “Global Dimming.” The premise of this program was that particulates migrating to our upper atmosphere were reflecting more and more sunlight back out into space (global dimming) … therefore causing global cooling. These particulates, of course, are mostly man-made … from car and plane combustion emissions, power plant exhausts, and other hydrocarbon burnings. (They conveniently ignore massive dust storms, volcanic eruptions, forest fires, intrusions of space dust, and other natural causes.)
The drama of this premise was that this global cooling is partially canceling out the global warming caused by mankind’s creation of greenhouse gasses (mostly carbon dioxide). Therefore, it was stated (gasp) that our attempts to remove particulate pollution from our environment would, in effect, speed up the process of global warming! The estimate was that global dimming has more than halved what would have been the effect of greenhouse gases on our global temperature rise (about one degree Fahrenheit over the last 40 years.) It was also estimated (by a starry-eyed scientist) that, by the end of this century, global warming would increase by as much as twenty degrees and that this would melt the Greenland ice cap and that this, in turn, would flood out all of Florida (talk about dramatic graphics!) Oh, yes … and polar bears would have disappeared. They would swim and swim looking for sea ice … and eventually drown.
It was then stated that the last time global temperatures rose dramatically was about three million years ago when a “natural” increase in carbon dioxide caused an episode of global warming of this magnitude. My question is “Why is an increase in carbon dioxide of this magnitude in prehistory 'natural' whereas what is happening now 'unnatural'”? Have all the justifications for this prehistoric episode disappeared?
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