Geoscience Reference
In-Depth Information
patches on the sun's surface, carefully recording their locations and numbers,
and noticed that the number and positions of the dark patches shit ed from
year to year. Galileo and other astronomers recorded a ten- to twenty-fold
decrease in these dark spots beginning in AD 1645. For the next seventy years,
between AD 1645 and 1715, the sun's surface was almost devoid of sunspots.
In the late nineteenth century, the sunspot records were reexamined by
astronomer Edward Walter Maunder. h is period of low sunspot numbers
from AD 1645 to 1715 is now known as the “Maunder Minimum.” Maunder
noted that this period coincided with the peak of the Little Ice Age, the cool
interval between the i t eenth and nineteenth centuries, and he proposed a
relationship between sunspots and climate.
Two other periods of low sunspot activity occurred during the past millen-
nium: the “Wolf Minimum,” peaking at AD 1300, and the “Sporer Minimum,”
peaking at AD 1500. h ese, and the Maunder Minimum, are spaced about
200 years apart, remarkably similar to the recurrence intervals of extreme
climate events—l oods and droughts—in the American West and elsewhere
across the globe. In the West, these extreme events were recorded in the strati-
graphic records of megal oods in the Santa Barbara Basin, changing lake levels of
Mono Lake, and l uctuating salinity in the San Francisco Bay, to name just a few.
h e pattern recurs beyond the western United States. For example, severe
l oods and droughts have been found to recur every two centuries in Central
America. h e Mayan empire of the Yucatan, which had l ourished for thousands
of years, was buf eted by periodic droughts and ultimately collapsed at the peak
of its power nearly 1,000 years ago. h e Mayans had long kept records of astro-
nomical phenomena, and the droughts coincided with a pronounced 208-year
cycle of increased solar intensity, a fact they may have noted with grave concern.
h
e Sunspot-Climate Connection
Although the connection between sunspots and climate is intriguing, the
causal mechanism remains somewhat mysterious. h e change in solar energy
received by the earth between solar sunspot maxima and minima is a mere
one-tenth of 1 percent. How could such a small change cause such relatively
large climate shit s on the earth?
Sunspots appear when loops of magnetism form deep within the sun and
rise to the surface, leading to a drop in temperature that appears as a dark spot
when viewed from the earth. During periods with more sunspots, solar out-
put is greater, with more solar energy being received at the top of the earth's
