Climate Change: Real and Imaginary

Does the world face a future where the relatively benign climate the world enjoyed during the 20th century will become much more hostile? History suggests that it may. Scarcely a week goes by without scientists announcing new evidence of massive past climate disruptions. For example, a recent paper in Nature described the historical behavior of Africa’s climate, based on an examination of 1,100 years’ worth of sediments extracted from a 20-foot soil core from Kenya. The authors found a pattern of catastrophically severe, extended droughts alternating with wetter periods. In the words of Dr. Dirk Verschuren of the University of Minnesota: “We have to anticipate that a major catastrophic drought will happen sooner or later”…most likely within the next 50 to 100 years. And closer to home, researchers have discovered that the depression-era Dust Bowl, the worst U.S. drought of the 20th century, which forced the emigration of 60 percent of the people it affected, was typical of droughts that have struck the U.S once or twice a century since 1600 or so.

Other natural climate changes occur with greater frequency than these once-or-twice-a- century catastrophes. We have all heard about El Niño and La Niña, oscillations in the temperature of the Pacific Ocean which disrupt world weather patterns every few years. But a larger scale phenomenon, the Pacific Decadal Oscillation, changes average ocean temperatures every twenty or thirty years. Oceanographers at the Jet Propulsion Laboratory believe that the Pacific has recently flipped from the warmer state of the past quarter-century into a cooler state resembling that which prevailed between the 1940s and the 1970s. Some climate watchers then feared that falling global temperatures heralded the approach of a new ice age. In the early 1980s, when the average global temperature began to rise again, some of the same researchers and their younger successors began sounding the alarm about global warming. They attribute part of the 1o F rise in average global temperature over the course of the 20th century to steadily increasing atmospheric levels of carbon dioxide and other man-made “greenhouse gases, ” and some assert that unless greenhouse emissions are curbed, we may face catastrophic climate changes including devastating floods, calamitous droughts, super hurricanes and killer heat waves.

These forecasts of global warming are based on computer simulations of the world’s climate, which give divergent results depending on the particular model used, and are far too crude to credibly forecast how climate is likely to change on any scale less than hemispheric. Even ignoring these caveats, the modelers’ average estimate of greenhouse warming for the entire 21st century is about 3.5o F, or about one-thirtieth of a degree per year. That is far less than the unpredictable temperature fluctuations that occur annually, so its effects from year to year should be far smaller than natural weather disruptions.

In the United States, the death toll from floods and hurricanes has decreased in large measure because people are able to escape in time, thanks to improved warning time and the virtually universal ownership of private automobiles whose emissions so exercise the prophets of global warming. Improving the ability of the rest of the world to cope with natural disruptions will also come with increased mobility and greater engineering capability. That will require using all the resources of material and energy at our disposal. It would be foolish to restrict their use for fear of global warming, a minor source of disruption compared with Mother Nature.

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