Those tree rings also showed that during six decades, from 1568 until 1634, there was, because of natural climate variation, six decades of expansion of the subtropics, which pushed desert climates north. Because of expanding zones of hot and dry weather, the Ottoman Empire in Turkey ended, the Ming dynasty collapsed and the Jamestown colony in Virginia was abandoned, suggesting, Dr. Trouet said, they were in part at least, climate-related. “The way society handles a drought politically is also part of the picture,” she said.
Other sources — lake sediments; ice core samples; coral; the otolith, or ear bone, of fish; and even the shells from living and long dead geoducks, a large bivalve with a snakelike appendage — add to the broader picture.
“We have divers sucking up ancient geoducks off the ocean floor,” said Bryan Black, a professor of dendrochronology who also specializes in marine organisms. Combined with long dead geoduck shells, data could go back many thousands of years. Shells from the coast of Iceland already go back 1,000 years. “They show that the last century is unprecedentedly warm,” Dr. Black said.
Experts are using the shell ring information, combined with tree ring data, to understand how climate drives ocean productivity and the species mix of fish, to assist fisheries managers. “The bottom line is to be aware of climate whiplash and what that means for fisheries,” Dr. Black said.
Even the stars give up some of their secrets to trees. The sun and other stars emit radiation called Galactic Cosmic Rays, or G.C.R.s, that react in the atmosphere with nitrogen and change the levels of carbon 14, which is taken up by every living thing and becomes a tracer for cosmic ray levels.
Past spikes in G.C.R.s from solar flares or other sources are largely a mystery, but have attracted keen interest from researchers, because if they occur now they could wipe out communication satellites and other technology. An event in 744, first found in Japanese cedar trees and since found globally, is the strongest cosmic ray event in the tree ring record, a magnitude larger than the Carrington event, a solar storm in 1859, and apparently noted by people alive at the time.
“This year also appeared in the heavens a red crucifix, after sunset,” was how the Anglo-Saxon Chronicles reported the event in the mid-eighth century.
It was most likely a huge solar flare. “It is unprecedented, there’s nothing else like it,” said Charlotte Pearson, a professor at the tree ring lab. “We’re trying to work out what it is and what caused it but we’re still not sure.”
