Ancient Cave Clues Point to Future Drought

URL: http://www.abqjournal.com/news/metro/537245metro02-11-07.htm

Sunday, February 11, 2007
Ancient Cave Clues Point to Future Drought
By John Fleck
Albuquerque Journal Staff Writer

Pink Panther Cave seems an odd place to study the vagaries of New Mexico drought. Deep beneath the Guadalupe Mountains in southern New Mexico, the temperature sits reliably in the low 50s, day in, day out, winter, summer. It never rains, save the steady drip, drip, drip from the cave's ceiling.

In those drips, though, scientists see an unsettling story of drought in our future. As the slow dripping created the stalagmites in Pink Panther Cave, it left traces of the climate above. In those traces, University of New Mexico professor Yemane Asmerom see signs of a climate that has in the past turned dry under conditions similar to the global warming predicted over the next century.

"Things don't bode well for the Southwest," Asmerom said in an interview.

The prediction is not a perfect fit. In the past, it was slight variations in the sun that heated things up. This time, it is greenhouse gases, emitted by humans burning fossil fuels.

But if the effect on climate is the same, Asmerom and a team of colleagues wrote in the latest issue of the scientific journal Geology, the warming could lead to "persistent hyperarid conditions."

Located on U.S. Forest Service land in the Guadalupe Mountains of southeastern New Mexico, Pink Panther Cave's name is a bit of misnomer.

The "pink" comes from a stain on the ground around the cave's mouth, left by firefighters who used red fire retardant in an aerial attack on a forest fire, according to Victor Polyak, one of Asmerom's UNM colleagues on the project.

The "panther" comes from a pile of bones found inside the cave's entrance. The name is a case of mistaken identity. The sad creature that made its fatal fall into the cave's mouth was not a cat at all. "It's a bear," Polyak said.

Where the bear fell, modern cavers must lower themselves some 50 feet by rope into the cave's beautifully decorated main room.

That is what the team of scientists did in September 2003 when they went, Forest Service permit in hand, in search of a stalagmite to use for their climate study.

Stalagmites and other cave formations?- "speleothems" is the scientific word?- are increasingly attractive to scientists trying to understand ancient climate.

In most parts of the world, New Mexico included, there have only been rain gauges and thermometers to record the weather for a little more than a century.

To figure out what happened before, scientists are exploiting a growing arsenal of tricks, from layers of ice in Antarctica to corals that grow differently depending on whether the water around them is warm or cold.

In New Mexico, tree rings have long been scientists' tool of choice. But tree ring records here only go back 2,000 years. Asmerom has turned to cave formations to push the climate record back in time.

The idea is that changing rainfall patterns on the mountains above Pink Panther Cave are reflected in the growth patterns of the cave's stalagmites. Asmeron and his colleagues painstakingly analyze the stalagmite's layers in a University of New Mexico lab to tease out the story.

Their Pink Panther Cave stalagmite goes back 12,000 years, to the end of the last ice age. As such, it gives them a climate record spanning the whole of the warm, climatically stable period in which human civilizations grew.

The great droughts that marked the end of the last ice age, as ancient lakes that once spread across New Mexico evaporated, show up in the scientists' cave record, as do brief wet spells that temporarily refilled lakes like Estancia east of Albuquerque.

The question is why.

Asmerom and his colleagues found that the wet and dry spells match up reasonably well with other records of the sun's activity. A more active sun means more drought here, they suggest.

They think the answer has something to do with the sun's effect on the Pacific Ocean, a key ingredient in storm patterns and, therefore, drought here.

Columbia University climate researcher Mark Cane, who has worked on the climate-sun-ocean problem, agrees. "It's a very interesting and important paper," Cane said of Asmerom's new work.

But Penn State's Michael Mann, who has worked with Cane on the link between past droughts and future global warming scenarios, cautions that the scientific question is still not settled.

The problem, Mann explained, is that it is not yet clear whether the ocean will behave the same in a greenhouse warming world as it did in the past when changes in the sun were doing the work.