Oct. 27, 2004 — The sun is in the thick of one of the longest and stormiest periods in 8,000 years, say researchers who have tracked down an 11,400-year record of stormy sunspot activity in tree rings.

Until now, scientists could only study sunspot records back to 1610, when astronomers started keeping track of sunspots by direct observation. Now, thanks to a clever new method, the 400-year sunspot record can be extended back to the Ice Age.

The new sunspot record was presented in an article in this week's issue of the journal Nature.

"The authors (of the Nature article) did show that their sunspot number reconstruction matched the observed sunspot record quite closely from circa 1610 — 1900 A.D.," said carbon-14 specialist Paula Reimer, director of the Center for Climate, the Environment & Chronology at Queen's University in Belfast, Ireland. "So this does provide a test of the method."

The new method works like this: Trees and tree rings contain carbon, which they get from carbon dioxide in the atmosphere. Some of that carbon is the isotope carbon-14 which is created in the Earth's atmosphere by cosmic rays flying in from outside the solar system.

But those cosmic rays can't reach Earth when the sun is stormy with sunspots and the solar wind is roaring. So a tree ring containing low carbon-14 is a sign of few cosmic rays in that growth year, which is an indicator of a stormy sun, contend Max-Planck-Institut für Sonnensystemforschung's Sami Solanki and colleagues.

Most striking in the new sunspot archive derived from the new method is how much today's ongoing stormy period stands out from past periods, the researchers said.

"During the last eight millennia, the episode with the highest average sunspot number is the ongoing one that started about 60 years ago," reported Solanki.

And although 11,400 years is merely a moment in the multi-billion-year life of the sun, it is enough to contain a record of 31 high sunspot periods which average about 30 years in length, the researchers said.

The longest is 90 years long. That is enough of a sample to enable the researchers to venture a guess about how long the current stormy period will last.

"The probability that it will continue until the end of the twenty-first century is below one percent," the researchers conclude.

As for whether the last few decades of storminess on the sun is the cause of global warming over the same period, it's not likely, said Reimer.

"The increased solar activity may account for part of the climate trend and it does come at a bad time," she said. "However, in terms of actual warming it probably isn't a large contributor."