National Geographic : 2004 Sep
pollen in the mud, Whitlock takes smudges from every core at set intervals, then puts the mud in a chemical bath that eats away everything but the thousands of previously invisible pollen grains. She places a droplet of the pollen resi due on a slide and then "reads" about 300 grains, identifying the species of each one-a process that allows her to trace how the vegetation in the Coast Range changed during the climatic variations of the past. "You hit bedrock at the lake at about 18.25 meters," Whitlock says, placing a sample slide beneath her microscope. "The pollen at that level dates to about 42,000 years ago." Very few mountain lakes have such a contin uous record, she adds, since they are often formed when glaciers retreat. But a landslide that blocked a small stream before the last ice age made Little Lake. The pollen in its muddy sediments "tells us what the coastal Oregon environment was like before and at the height of that ice age and how it changed as the climate warmed about 13,000 years ago," says Whitlock. "It was a big change," she continues. "Here's what the forest looked like 21,000 years ago at the height of the last ice age. And, oh man, was it a different world." I take her place at the scope, and she guides me from grain to grain. It's a surprisingly easy tour, since there are really only two types of pollen on this slide: the large, kidney-shaped grains of Engelmann spruce trees, and the smaller grains of mountain hemlock, which look like ovals with two small ears. "Now think about this," Whitlock says. "Engelmann spruce doesn't grow in the Coast Range today. Instead, you find Douglas fir; that's the dominant conifer. But there isn't any Doug fir pollen on that slide. Doug fir doesn't show up until close to the end of the last ice age, and then-suddenly boom!-it's there and the spruce forest is gone. And that happens in 200 to 500 years: A whole forest vanishes and another one takes its place." Whitlock pauses. "So we want to know how that happened and why. What caused the forest and the climate to change so dramatically and abruptly? And what happens if the climate shifts in the other direction, toward an ice age again or toward even warmer conditions? How are we-people-going to respond?" 62 NATIONAL GEOGRAPHIC * SEPTEMBER 2004 ce cores from Greenland, first obtained and analyzed in the 1960s, gave scientists early clues to rapid climate change. Because the ice there has accumulated undisturbed for over 100,000 years, it holds some of the best records for such things as past temperatures, amount of precipitation, and atmospheric conditions. The Greenland cores, combined with even older ice cores from Antarctica's Vostok Station, showed the expected long periods of gradually increasing cold followed by shorter warm peri ods. But the Greenland ice also revealed that within the long, cold stretches there were short periods of warming and cooling. These shorter changes came in bursts, causing the climate to jump from cold to hot to cold again, sometimes in mere decades. The past climate had behaved like "an impish three-year-old" flicking a light switch, as Richard B.Alley, one of the scientists on the early 1990s Greenland drilling project, Frozen History Lonnie Thompson of Ohio State Univer sity holds an ice core from Peru's Quelc caya ice cap, which is retreating 40 times faster today than in the 1960s. Thompson's freezer may soon contain the sole remains of tropical glaciers from around the world, including the famed snows of Mount Kilimanjaro, which could vanish in 15 years. "What glaciers are telling us," says Thompson, "is that it's warmer now than it has been in the last 2,000 years over vast areas of the planet."