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Mercury, May/June 2003 Table of Contents

Courtesy of William C. Livingston (Kitt Peak National Solar Observatory).

by Willie Soon and Steven H. Yaskell

A weak solar maximum, a major volcanic eruption, and possibly even the wobbling of the Sun conspired to make the summer of 1816 one of the most miserable ever recorded.

The year 1816 is still known to scientists and historians as "eighteen hundred and froze to death" or the "year without a summer." It was the locus of a period of natural ecological destruction not soon to be forgotten. During that year, the Northern Hemisphere was slammed with the effects of at least two abnormal but natural phenomena. These events were mysterious at the time, and even today they are not well understood.

First, 1816 marked the midpoint of one of the Sun's extended periods of low magnetic activity, called the Dalton Minimum. This particular minimum lasted from about 1795 to the 1820s. It resembled the earlier Maunder Minimum (about 1645-1715) that was responsible for at least 70 years of abnormally cold weather in the Northern Hemisphere. The Maunder Minimum interval is sandwiched within an even better known cool period known as the Little Ice Age, which lasted from about the 14th through 19th centuries.

But the event that most severely shaped 1816's cold phenomena was the cata-strophic eruption the previous year of Tambora on the island of Sumbawa, in modern-day Indonesia. The ash clouds and sulfur aerosols spewed by this volcano were widespread, chilling the climate of the Northern Hemisphere by blocking sunlight with gases and particles.

A third factor also could have played a role. During both the Dalton and the Maunder minima, the Sun shifted its place in the solar system — something it does every 178 to 180 years. During this cycle, the Sun moves its position around the solar system's center of mass. This particular trick of gravity is known as "inertial solar motion." Scientists have not yet confirmed whether or not inertial solar motion affects Earth's climate directly, but it remains a possibility.