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Cave clue points to drier Southwest

Image: Fort Stanton Cave
New Mexico's Fort Stanton Cave has yielded clues to what warmer temperatures would mean.Bureau of Land Management
/ Source: Discovery Channel

Global warming will likely lead to dramatic poleward shifts of Earth's wettest storm-laden weather patterns, according to a remarkable 56,000-year-old stalactite found in a New Mexican cave.

This means some places, like New Mexico, could dry up while others, like some parts of China, will become very, very wet.

This remarkably specific climate change forecast comes from the careful study of a record contained in the mineral layers of a stalactite (a mineral dripstone) found in Fort Stanton Cave of southeastern New Mexico.

The stalactite provides an unusual glimpse into the past because of chemical signatures in the calcite layers. Different forms of oxygen within the minerals make it possible to distinguish water that rained or snowed down from wintry jet stream-powered Pacific Ocean storms versus the state's annual summer monsoon rains from the Gulf of Mexico.

What the stalactite reveals are big shifts in these precipitation patterns over the millennia, explained University of New Mexico researcher Yemane Asmerom, who is the lead author of a letter describing the discovery in the latest online issue of Nature Geosciences.

It wasn't until the researchers compared the mineral record to temperature records extracted from Greenland ice cores did it start to make any sense in the bigger climate change picture.

It turns out, said Asmerom, that whenever the Greenland ice shows a warm period, the New Mexico stalactite shows less rainfall and snow coming from the Pacific Ocean. That suggests the warmer periods are causing the jet stream — which brings in Pacific storms — to retreat northwards, taking the winter moisture with it.

But that's not all they found. The researchers also discovered a remarkably similar stalactite precipitation record from Hulu, China (a suburb of Shanghai). That record mirrors the New Mexico pattern of dry/wet periods but in reverse: When the climate is warmer and New Mexico dries up, Hulu gets drenched.

"It's one of the best matches I've ever seen," said Asmerom of how well the three records match. "It's almost like a photocopy."

What it suggests is that not only is the jet stream forced poleward during bouts of global warming, but the equator-straddling bands of moisture that keep tropical regions green also shift poleward, enveloping Hulu, China, among other places.

This regional picture of change is something that climatologists had suspected from previous analyses of decades of meteorological data. But they could not confirm it, until now.

"Asmerom and his team looked at completely different data and yet they were able to make a hypothesis of what happened to the jet stream and the (tropical rainfall zone)," said Cristina Archer, a geoscientist at California State University at Chico. Archer was involved with the modeling of 28 years of meteorological data which, among other things, hinted strongly of the very same thing Asmerom and his team are seeing in the cave's mineral record.

"There were a lot of findings (from the modeling work), but shifts towards the poles was one of them," Archer said.

In other words, the stalactite mineral records are pretty good independent confirmation that there is something to this pattern of changes that will come with a hotter planet.