In 1994 The NYT Knew The Real Truth About Californian Droughts

By Paul Homewood 

 

h/t Don B

 

http://www.nytimes.com/1994/07/19/science/severe-ancient-droughts-a-warning-to-california.html?pagewanted=1

 

There was a time when you could get proper journalism from the New York Times. This is what they reported in 1994:

 

BEGINNING about 1,100 years ago, what is now California baked in two droughts, the first lasting 220 years and the second 140 years. Each was much more intense than the mere six-year dry spells that afflict modern California from time to time, new studies of past climates show. The findings suggest, in fact, that relatively wet periods like the 20th century have been the exception rather than the rule in California for at least the last 3,500 years, and that mega-droughts are likely to recur.

The evidence for the big droughts comes from an analysis of the trunks of trees that grew in the dry beds of lakes, swamps and rivers in and adjacent to the Sierra Nevada, but died when the droughts ended and the water levels rose. Immersion in water has preserved the trunks over the centuries.

Dr. Scott Stine, a paleoclimatologist at California State University at Hayward, used radiocarbon dating techniques to determine the age of the trees’ outermost annual growth rings, thereby establishing the ends of drought periods. He then calculated the lengths of the preceding dry spells by counting the rings in each stump.

This method identified droughts lasting from A.D. 892 to A.D. 1112 and from A.D. 1209 to A.D. 1350. Judging by how far the water levels dropped during these periods — as much as 50 feet in some cases — Dr. Stine concluded that the droughts were not only much longer, they were far more severe than either the drought of 1928 to 1934, California’s worst in modern times, or the more recent severe dry spell of 1987 to 1992.

In medieval times the California droughts coincided roughly with a warmer climate in Europe, which allowed the Vikings to colonize Greenland and vineyards to grow in England, and with a severe dry period in South America, which caused the collapse of that continent’s most advanced pre-Inca empire, the rich and powerful state of Tiwanaku, other recent studies have found.

 

Dr. Stine, who reported his findings last month in the British journal Nature, says that California, like Tiwanaku, presents "a classic case of people building themselves beyond the carrying capacity of the land," which is determined not by wet times but by dry ones. "What we’ve done in California is fail to recognize that there are lean times ahead," said Dr. Stine, "and they are a lot leaner than anything we’ve come up against" in the modern era.

How far ahead that reckoning might lie is, of course, uncertain. But one ominous sign may be that the earth’s climate as a whole is now warming up, whether from natural causes or because of heat-trapping atmospheric gases emitted by industrial society. Any significant global warming would probably cause changes in atmospheric circulation and precipitation patterns, and the new findings suggest that "during much of medieval time the planetary ocean-atmosphere system operated in a mode unlike that of modern time," Dr. Stine wrote in Nature.

This alteration of the system could well have been caused by a natural global warming, he said. He believes that one long-term effect was to steer storm tracks and rainfall away from California. If this pattern was indeed brought about by a medieval global warming, he said, a future global warming — whether natural or human-induced — might bring back the decades-long droughts of yore.

Dr. Stine’s findings, combined with similar evidence he turned up in Patagonia, strengthen the case of those who believe that the earth experienced a general warming at the time of the Middle Ages, Dr. F. Alayne Street-Perrott, a paleoclimatologist at Oxford University in England, wrote in a commentary accompanying Dr. Stine’s report in Nature. Other experts maintain that the medieval warming was not global but instead affected only some parts of the world.

 

In the period separating the two long droughts, Dr. Stine said, the water in Mono Lake rose to a level higher than any in the last 150 years, suggesting that the California climate was even wetter then than it is today. The last century and a half, Dr. Stine found, has been the third wettest period in the last three millenniums. But, he said, "the vast majority of years during the past 3,500 years have been much drier than what we’ve come to expect to be normal in California."

 

 

Like Tiwanaku’s engineers, those who draw up California’s water-management plans do so on the basis of what are believed to be normal droughts but in fact are not nearly as severe as what has occurred in the past and can occur again, said Dr. Stine.

"The assumption they’ve made for a long time — that California is subject to droughts of a maximum of seven years — could be harmful in the long run," he said, because "they have doled out water on that assumption.

"This could be destructive if you get hit with a 9th or a 10th or a 15th year of severe drought."

In gauging the length and frequency of droughts for planning purposes, California officials rely on a tree-ring study extending back to about 1560. Over that period, the 1928-1934 drought was the longest and worst. The problem, said Dr. Stine, is that the study period includes not only the wet 19th and 20th centuries, but also the even wetter 16th and 17th centuries. "They’re using the wettest period of the last 3,000 years to define the duration and severity of the droughts we can expect in the future," he said.

 

 

Apart from the history of mega droughts, with which we are familiar, perhaps the most significant point raised is that the last century and a half has been the third wettest period in the last three millenniums.

California clearly needs to recognise this reality and forget about blaming everything on CO2.