What was the "Little Ice Age?"

The Little Ice Age was a period from 1300 to 1850 A.D. when the Northern Hemisphere experienced colder than normal temperatures.

Some scientists say that a major volcanic eruption in 1258 A.D. and another in 1600 A.D. helped cool temperatures in the Northern Hemisphere. The coldest period of the Little Ice Age is attributed to lower than normal solar energy.
From 1410 to the 1720s the cooling had a strong effect on some areas. During that time, access to Greenland was largely cut off by ice. 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.

Unusually low solar activity, indicated by little or no sunspot activity, between 1645 and 1715 likely triggered the Little Ice Age in Europe and North America. During this event, known as the Maunder Minimum, astronomers observed only about 50 sunspots over 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 cycle, it goes from a minimum to a maximum period of activity represented by a peak in sunspots and flare activity.

During those periods of low solar activity, levels of the sun's ultraviolet radiation decrease which can significantly impact ozone formation in the Earth's stratosphere. A lag time of 10-30 years allowed for the climate system to be affected by an increased ozone layer that altered the heating of the oceans. Diminished jet stream winds caused by a dimmer sun created cold land temperatures by reducing the movement of warm Pacific air to America and warm Atlantic air to Europe. During this shift, winter temperatures cooled as much as 2 to 4 degrees F - enough to freeze rivers and alter agriculture, economy, disease, etc.

For more information:
http://www.gsfc.nasa.gov/topstory/20011207iceage.html

This week's question comes from Rob Gutro. Rob is a meteorologist who works at NASA Goddard in Public Affairs. He did forecasting for the Weather Channel Radio Network, was a technical writer for NOAA, provided broadcasts on NOAA Weather Radio in Baltimore, and was a radio personality for 20 years in various cities.