This post was first published on Dec. 6, 2013, on the Earth Institute’s State of the Planet blog. It was updated on Oct. 14, 2014 (see below).
Guleed Ali pauses to study his notebook, standing on a steep slope covered in gray volcanic ash and desert brush, high above the present-day shore of Mono Lake in eastern California. He looks across the slope to where, a few hundred yards away, a gash of lighter gray sediment cuts across the hill, then disappears. The exposed sediment is history: A record of deposits left by Mono Lake when it stood far higher than today.
Ali picks a spot, hefts his shovel and begins clawing into the slope, raising puffs of dust, searching for a missing page in that sediment history: something higher upslope, evidence of the stream that would have fed the prehistoric lake: a layer of gravel. He finds only sand – perhaps an ancient beach. He moves across the slope, lifts and plunges his shovel back into the soft hillside.
He is digging for dates, looking back tens of thousands of years into the last ice age: When was the lake higher? When did it shrink, and grow again? How does that chronology correspond with the advance and retreat of the massive ice sheets that covered much of North America? And how did the lake’s levels respond to changing climate?
Understanding that past will help scientists like Ali, a PhD student at Lamont-Doherty Earth Observatory, project what might happen in the future as the world warms up. This is no esoteric question for Los Angeles, whose nearly 4 million people depend in part on Mono Lake’s watershed for drinking water, green lawns, agriculture and industry.