The Sun's Chilly Impact on Earth

A new NASA computer climate model reinforces the long-standing theory that low solar activity could have changed the atmospheric circulation in the Northern Hemisphere from the 1400's to the 1700's and triggered a "Little Ice Age" in several regions including North America and Europe. Changes in the sun's energy was one of the biggest factors influencing climate change during this period, but have since been superceded by greenhouse gases due to the industrial revolution.

During the Little Ice Age, access to Greenland was largely cut off by ice from 1410 to the 1720's. At the same time, canals in Holland routinely froze solid, glaciers advanced in the Alps, and sea-ice increased so much that no open water was present in any direction around Iceland in 1695.

Drew Shindell of Goddard Institute for Space Studies and other researchers have used a computer model to reconstruct climate and atmospheric conditions from the present back to the Little Ice Age.

They determined that a dimmer sun reduced the model's westerly winds, cooling the continents during wintertime. Shindell's model shows large regional climate changes, unlike other climate models that show relatively small temperature changes on an overall global scale. Other models did not assess regional changes.

During the coldest part of the Little Ice Age, from 1645 to 1715, there is believed to have been a decrease in the total energy output from the sun, as indicated by little or no sunspot activity. Known as the Maunder Minimum, astronomers of the time observed only about 50 sunspots for a 30-year period as opposed to a more typical 40-50,000 spots. The sun normally shows signs of variability, such as its eleven-year sunspot cycle. Within that time, it goes from a minimum to a maximum period of activity represented by a peak in sunspots and flare activity.

For the complete article on the study of the climate and atmospheric conditions, go to: http://www.gsfc.nasa.gov/topstory/20011207iceage.html