A study of North Atlantic ice suggests that the brightening and dimming of the sun may cause a 1,500-year cycle of cooling and warming on parts of the Earth. Researchers have found that a very slight difference in the amount of solar energy reaching the Earth can have a powerful effect on the climate. As ice builds up in lands bordering the North Atlantic, the average temperature drops in Europe and North America.

Gerard C. Bond, a researcher at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, New York, says, ?Whether the whole Earth is affected, we don?t know for sure yet, but it is certainly implied. The effect does extend from the high northern latitudes down, maybe even to the tropics.?

Based on analysis of the past 12,000 years, the cycle of sunlight intensity roughly follows a 1,500-year pattern, although the difference in energy levels from the top of the cycle to the bottom is less than 0.1 percent. But Bond and his colleagues believe this is enough to trigger severe climate changes, such as the Little Ice Age, a 490-year period starting in 1400 in Europe and the North Atlantic. ?The climate system is extremely sensitive to weak forces, such as solar variability,? says Bond. ?That should make us that much more worried about greenhouse warming.?

The 1,500-year cycle of warming and cooling corresponds to data from tree ring studies, which is one way of measuring the sun?s strength over time. When the sun is at its most energetic, it strengthens the Earth?s magnetic field, which blocks more cosmic rays. When cosmic rays hit plants, they cause the formation of the isotope carbon-14, which can be measured in ancient tree rings. A tree ring rich in carbon-14 suggests an inactive sun. These findings agree with studies measuring the chilling of the Earth based on the advance and retreat of alpine glaciers in Europe.

Bond says the Earth?s temperature is still recovering from the Little Ice Age, when ocean temperatures dropped by two to three degrees. That change was enough for ice to jam most of the North Atlantic, closing many ports in the winter and affecting the weather throughout Europe. Rivers that never freeze now were routinely used for ice skating then.

Based on the 1,500-year cycle, Bond believes the Earth?s next little ice age could occur about the year 3100, plus or minus 500 years.

To learn more about this, read ?The 23rd Cycle? by Sten Odenwald,click here.

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