The researchers then used these established relationships to extrapolate further back in time and reconstruct more accurate accounts of sea temperatures over the past 150 years—about twice as far back as written records go in the northeastern Pacific.
"Anytime you get something older than the written record, you are making progress," Copenheaver says.
Critical information for climatologists
"My students always ask," Copenheaver adds, "'Are we experiencing climate change?' And I tell them, 'That's not the important question. The real question is whether or not the change we are experiencing is unprecedented. Have we ever had changes this fast, and to this great extent?'"
Climatologists see power in the new proxy combo to help answer these questions. "This sort of work can help in a very real way," says Michael Mann, director of the Earth System Science Center at The Pennsylvania State University and lead author of the IPCC's third report. "Piecing together complementary information from various archives can help us sort out some of the current uncertainties of model projections of future climate change."
As detailed in the most recent IPCC report, Earth's average temperatures can be traced back more than 1,000 years—primarily through ice core samplings. But what remains unclear is the spatial pattern of that record, explains Mann, who was not involved in the geoduck research. "It's easier to figure out how warm it was in general than to figure out exactly where it was warmest, and where it was not quite as warm," he says. "There is a lot of heterogeneity in the climate system."
A lot of that variation intrinsically involves the oceans. So, knowing what is going on in the ocean is essential for an understanding of the basic dynamics of the climate, Mann says, pointing specifically to the El Niño phenomenon in the Pacific. He notes that El Niño patterns are known to influence rainfall in Africa, tropical cyclones in the Atlantic, winter weather in North America, and droughts in the U.S. southwestern desert.
"We can project meaningfully what the average temperature of the globe will be, but there's quite a bit of uncertainty about how El Niño will change," Mann adds. "It's a little bit of a dirty secret that there is very little consensus on something that fundamental." But, he adds, "using geoducks combined with tree rings can better pin down [El Niño] patterns."
Ugly geoducklings wanted: Dead or alive
The proxy combination is not without limitations. Whereas trees can live 500, even 1,000 years, geoducks' life spans typically don't exceed 150 years. Still, short chronologies can be valuable where the written record is short—like in the northeastern Pacific. And scientists are now looking to dig up dead geoducks in sea sediments to further extend that range, Black says.