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Global warming: Some inconvenient glaciers

By Dennis Avery
web posted June 12, 2006

Al Gore says the world's glaciers are melting because humanity has emitted too much CO2.

However, a new peer-reviewed study shows that in South America's Andes Mountains the glaciers' advances and retreats have not been governed by CO2, but by small variations in the sun's intensity.

The study, led by P.J. Polissar of the University of Massachusetts, found that Andean glaciers expanded only four times during the 600 years of the Little Ice Age, which lasted from 1250 AD to 1850. Each of those glacier advances occurred during a solar minimum, when the sun's lowered activity apparently dropped the mountain-top temperatures by 2–4 degrees C and increased precipitation by about 20 percent.

The Polissar team's report, "Solar Modulation of Little Ice Age Climate in the Tropical Andes," was recently published online in the Proceedings of the National Academy of Sciences.

The team studied the glaciers' moraines -- piles of rocks, soil, tree trunks and other glacial debris left behind when the glaciers retreated. Then they matched the glacial debris with the sediment layers in nearby mountain lakes. The pronounced seasonality in the Andes precipitation allows the researchers to count years in the sediments and precisely date the glacial advances.

The Andes glacier study not only links glacial advances and retreats with the sun, but emphasizes that the earth's glaciers have often retreated -- and even disappeared -- during past centuries, long before humans built cars and smokestacks.

Most of the Andes glaciers must have disappeared during the Holocene Warming that ended just 5,000 years ago. Temperatures then were as much as 2 degrees C warmer than today's. So far, the Modern Warming has produced about only 0.8 degrees C of total temperature rise in its 150 years.

The sun has been linked to earth's climate changes for the past 400 years -- by sunspot records. Early astronomers noted that the two coldest periods of the Little Ice Age occurred when there were virtually no sunspots on the sun. The Sporer Minimum lasted from 1420 to 1570, and the Maunder Minimum from 1645 to 1710.

The solar-earth linkage came to the fore again in the 1980s, when researchers brought up the first long ice cores from Greenland and the Antarctic. The 400,000 years of temperature history contained in the ice cores clearly showed a moderate, natural cycle that raised temperatures at the latitude of New York and Paris by about 2 degrees C, and then lowered them by a similar amount. The cycles averaged about 1500 years in length. Carbon 14 and beryllium 10 isotopes in the ice clearly linked this temperature cycle to the sun.

The question for Al Gore is not whether our temperatures are rising; the key question is why they're rising. Antarctic ice cores tell us that temperatures and CO2 in the atmosphere have tracked closely together through recent Ice Ages, but the CO2 changes have lagged behind the temperature changes by about 800 years.

Higher temperatures have produced more atmospheric CO2, rather than CO2 producing higher temperatures! That's because most of the planet's CO2 is stored in the oceans, and as the seawater warms, it can't hold as much CO2.

If CO2 is the driving climate force, why did the earth begin warming in 1850, while human CO2 emissions didn't start to really expand until about 1940? Mr. Gore doesn't tell us the answer.

Why did the earth's temperatures decline from 1940 to 1975, even as CO2 emissions were soaring? Mr. Gore doesn't say.

How warm will New York get in the Modern Warming? Apparently Mr. Gore can't tell us, but a total of 2 degrees C seems likely -- based on the history in the ice cores.

Dennis T. Avery is a senior fellow for Hudson Institute in Washington, DC and the Director at the Center for Global Food Issues. He was formerly a senior analyst for the Department of State. Readers may write him at Post Office Box 202, Churchville, VA 24421.

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