A typical sunspot compared to the size of the earth. Sunspots have all but vanished in recent years

Dr. Kenneth Tapping is worried about the sun. Solar activity comes in regular cycles, but the latest one is refusing to start. Sunspots have all but vanished, and activity is suspiciously quiet. The last time this happened was 400 years ago -- and it signaled a solar event known as a "Maunder Minimum," along with the start of what we now call the "Little Ice Age." Tapping, a solar researcher and project director for Canada's National Research Council, says it may be happening again.

Overseeing a giant radio telescope he calls a "stethoscope for the sun," Tapping says, if the pattern doesn't change quickly, the earth is in for some very chilly weather. During the Little Ice Age, global temperatures dropped sharply. New York Harbor froze hard enough to allow people to walk from Manhattan to Staten Island, and in Britain, people reported sighting eskimos paddling canoes off the coast. Glaciers in Norway grew up to 100 meters a year, destroying farms and villages.  But will it happen again?