Sunspot
Activity at 8,000-Year High |
Sunspots
have been more common in the past seven decades than at any time in the last
8,000 years, according to a new historic reconstruction of solar activity.
Many researchers have tried
to link sunspot activity to climate change, but the new results cannot be used
to explain global warming, according to the scientists who did the study.
Sunspots are areas of
intense magnetic energy. They act like temporary caps on upwelling matter, and
they are the sites of occasional ferocious eruptions of light and electrified
gas. More sunspots generally means increased solar
activity.
Sunspots have been studied
directly for about four centuries, and these direct observations provide the
most reliable historic record of solar activity. Previous studies have suggested
cooler periods on Earth were related to long stretches with low sunspot counts.
From the 1400s to the 1700s, for example, Europe and
But a firm connection
between sunspot numbers and climate remains elusive, many scientists say.
Better record
The new study, led by Sami Solanki of the Max Planck Institute in
Cosmic rays constantly
bombard Earth's atmosphere. Chemical interactions create a fairly constant
source of stuff called carbon-14, which falls to Earth and is absorbed and
retained by trees. But charged particles hurled at Earth by active sunspots
deflect cosmic rays. So when the Sun gets wild, trees record less carbon-14.
While trees don't typically
live more than a few hundred years or perhaps a couple thousand, dead and
buried trees, if preserved, carry a longer record, "as long as tree rings
can be identified," said Manfred Schuessler,
another Max Planck Institute researcher who worked on the study.
The study's finding:
Sunspot activity has been more intense and lasted longer during the past 60 to
70 years than at anytime in more than eight millennia.
Sunspot activity is known
to ebb and flow in two cycles lasting 11 and 88 years (activity is
currently headed
toward a short-term minimum). Astronomers think that longer
cycles -- or at least long-term variations -- also occur. Scientists in other
fields have shown that during the past 11,000 years, Earth's climate has had
many dramatic shifts.
"Whether solar
activity is a dominant influence in these [climate] changes is a subject of intense
debate," says Paula Reimer, a researcher at Queen's University Belfast who
wrote an analysis of the new study for Nature. Why? Because
"the exact relationship of solar irradiance to sunspot number is still
uncertain."
In general, studies
indicate changes in solar output affect climate during periods lasting decades
or centuries, "but this interpretation is controversial because it is not
based on any understanding of the relevant physical processes," study
member Schuessler told SPACE.com. Translation:
Scientists have a lot to learn about the Sun-Earth connection.
Better understanding
The study's methods appear
solid: "The models reproduce the observed record of sunspots extremely
well, from almost no sunspots during the seventeenth century to the current
high levels," Reimer said.
The research could
eventually help scientists understand why the climate has changed in the past
and allow for better predictions of future change.
"The reconstructed
sunspot number will nonetheless provide a much-needed record of solar
activity," Reimer said. "This can then be compared with palaeoclimate data sets to test theories of possible
solar-climate connections, as well as enabling physicists to model long-term
solar variability."
Whatever the result, change
is likely to continue.
Solanki's team calculates that, based on
history, the chances of sunspot activity remaining at the currently high levels
for another 50 years is 8 percent. Odds are just 1 percent the solar exuberance
will last through the end of this century.