Friday, April 3, 2009

FIRESIDE CHAT: Global Warming

In recent decades, denial that human activities have significantly accelerated natural global warming in our post-glacial era has emerged, but finally dwindled with release recently of a series of multinational consensus reports by the United Nations Intergovernmental Panel on Climate Change (UN IPCC). These reports hammer the final nail in the coffin of deniers' main premise, that global warming occurs cyclically, and naturally follows global cooling and periodic glaciations ('ice ages'). As glaciation proceeds, tropical climates contract toward Earth's equator, while temperate and arctic climates expand.

The near extinction of global warming denial has given rise to the next line of defense by the same people, representing the same short-term interests. That is, we humans may be contributing significantly to global warming, but we are doing so after a recent ice age, so the result of our contribution to global warming still will produce temperatures and sea levels that are well within the cyclical range of global experience. A major scientific leg of this argument is the arguable (though not generally accepted) claim that solar activity cycles over a relatively short time frame (decades rather than millennia) account for much of global warming observed since the year 1900. By extension, solar evolution might have accounted for terrestrial climate cycles, relegating human activities to a secondary role in causing recent global warming. The subtext, sometimes implied rather than stated, is that human activities still cannot be viewed as planet threatening. Here I examine this particular claim, rather than debunk timeworn arguments used previously to deny significant human contribution to global warming.

We are about 200 years past the beginning of the Industrial Revolution and about 10,000 years out of the most recent ice age, which began about 70,000 years ago and peaked about 20,000 years ago. Clearly, human life was and remains compatible with glaciation. We are about 120,000 years out of the most recent interglacial period (between the two most recent ice ages). Also clearly, human life was and remains compatible with global warming as experienced in the most recent interglacial period. So, why worry about 200 years of industrial activity?

My answer is that natural cycles dictate that we will live and die, and our children and theirs will do the same… but we should not be complacent about the quality and duration of their existence. We especially should not compromise theirs to improve ours. We live now, not 120,000 years ago. New York City was built on once-flooded land, but the next cycle of rising sea levels will affect 10 million people in the New York Metropolitan Area. I don't know the exact number 120,000 years ago (before telephones, telephone books, and the US Census), but I'm sure that the number was a lot closer to zero than to a million, and probably a lot closer to zero than to a thousand. This statement can be repeated many times, each time substituting the name of a different coastal metropolis. Further, expansion of deserts, shortages of drinking water, and emergence of disease are additional stresses that will kill a significant fraction of people in non-coastal areas globally, especially in the tropics, where the effects will be most pronounced and the countries affected least equipped to adapt… and that's just the anthropocentric answer.


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