• The unusually beneficial climate of the past few decades may be degenerating, facing humanity with a new challenge to survival

The winter of 1780-81 was a particularly bitter one for the American Revolutionary forces. Washington’s troops hunkered down, ill-clothed and ill-fed, around their campfires at Morristown, N.J., while a few miles away British troops enjoyed the relative luxury of an occupied New York City. But even the British had their problems, for the winter was so cold that parts of New York harbor froze for weeks at a time, blocking movement of their powerful fleet. The ice even got thick enough to allow hauling cannons from Manhattan to Staten Island.

The colonists had struggled against devastating winters ever since establishment of the earliest settlements, when one of the few holidays celebrated by the stern Puritans was that of Thanksgiving — for a harvest bountiful enough to ensure survival until spring. Though they didn’t realize it, these hardy pioneers were trying to conquer a New World in the midst of some of the worst weather in over 2,000 years, a cold spell that had begun in the early 15th century and was to continue until around 1850, known to later climatologists as the “Little Ice Age.”

By constrast, the weather in the first part of this century has been the warmest and best for world agriculture in over a millenium, and, partly as a result. the world’s population has more than doubled. Since I940, however, the temperature of the Northern Hemisphere has been steadily falling: Having risen about 1.1 degrees C. between 1885 and 1940, according to one estimation, the temperature has already fallen back some 0.6 degrees, and shows no signs of reversal. Specific areas, of course, may experience changes markedly different from the average. During the warming period, temperatures in parts of Norway rose five times more than the hemisphere average, and since the cooling trend began again, Iceland’s temperature has dropped nearly 2.0 degrees. threatening continued existence of some crops. What will happen to the added billions of people if climatic conditions return to those prior to the turn of the century?

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The cooling trend observed since 1940 is real enough, he says, but not enough is known about the underlying causes to justify any sort of extrapolation. Particularly dangerous would be any attempt to generalize from even of a full-blown I0,000-year ice age, a shorter-term experience, like the bad weather in 1972 and following years, to prognosticate any future weather patterns. On the other hand, the cooling since 1940 has been large enough and consistent enough that it will not soon be reversed, and we are unlikely to quickly regain the “very extraordinary period of warmth” that preceded it. Even this mild diagnosis can have “fantastic implications” for present-day humanity, Wallen says.

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If global temperatures should fall even further, the effects could be considerably more drastic. According to the academy report on climate, we may be approaching the end of a major interglacial cycle, with the approach of a full-blown 10,000-year ice age, a real possibility. Again, this transition would involve only a small change of global temperature — 2 or 3 degrees — but the impact on civilization would be catastrophic. Scientists once thought the onset of an ice age would be very gradual, with glaciers slowly pushing down from the North, but recent studies of cored material taken from the sea bottom and remaining glaciers indicate the transition can be rather sudden — a matter of centuries — with ice packs building up relatively quickly from local snowfall that ceases to melt from winter to winter.

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Source: Science News, Vol. 107

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