Earth may have a 1,500-year temperature cycle that is governed by minor changes in the sunlight
the brightening and dimming of the Sun may account for a 1,500-year cycle of cooling and warming on parts of the Earth, suggests a study. The study was done by researchers at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, New York, usa. According to them, a very slight difference in the amount of solar energy reaching the Earth has a powerful chilling effect on the climate: ice builds up in lands bordering the North Atlantic and the average temperature drops in Europe and North America (Associated Press , November 16, 2001) . " Whether the whole Earth is affected or not, we don't know for sure yet, but it is certainly implied," said Gerard C Bond, the first author of the study. "The effect does extend from the high northern latitudes down, maybe even to the tropics," he added.
The researchers analysed rocks that were dropped to the Atlantic floor after being carried to sea by icebergs that broke off glaciers in Iceland and other northern islands. The rocks fell as the icebergs melted, says Bond. Thus, the farther south the rocks fell, the farther south the icebergs drifted, giving a measure of ocean temperature. To determine when the rocks were dropped, researchers dated the age of shells deposited at the same time and place.
The 1,500-year cycle of warming and cooling corresponds to data from tree ring studies, another way of measuring the Sun's strength over time. Bond said the Sun, at its most energetic, strengthens the Earth's magnetic field, which blocks more cosmic rays, a type of radiation streaking in from deep space. When cosmic rays hit plants, they cause the formation of certain isotopes, such as carbon-14, that can be measured in ancient tree rings. A tree ring rich in carbon-14 suggests an inactive sun, for example.
Measurements of the iceberg drift and the tree rings showed a similar cycle, Bond said. "The connection we observed is that the increases in icebergs and drift ice occur at the same time as the increase in carbon-14, which means the sun was weaker," said Bond. He added that the findings also agree with studies that measured the chilling of the Earth based on the advance and retreat of alpine glaciers in Europe. Bond said the Earth's temperature is still recovering from the Little Ice Age, a 490-year period starting in 1400 that dramatically chilled Europe and the North Atlantic. Based on the 1,500-year cycle, Bond said that the Earth's next little ice age could occur about the year 3100, plus or minus 500 years.
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