Ice Ages and Alaska
Imagine yourself in a spaceship approaching the earth, eighteen thousand years ago. The ice-covered Arctic Ocean is blindingly white in the early June sunlight, but not just the ocean -- all of Scandinavia and parts of Europe and the British Isles lie under a glittering sheet of ice as well. Drift ice fills the northern Atlantic, and the warm blue waters of the Gulf Stream, which you expect to see swinging north of Norway, flow directly across to Spain. As you continue westward, Long Island and Cape Cod are mere piles of rubble at the edge of an ice sheet that rivals the one in Antarctica today. A massive lobe of ice pushes south of what will someday be the site of the Great Lakes, and Canada is an unbroken wasteland of ice, bounded on the south by rushing summer meltwaters that will someday become the Missouri and Ohio rivers.
The North Pacific and Alaska come into view -- more ice? Yes, but not only ice. While the Coast and Alaska ranges are massive bastions of white, there are great lakes thawing under the summer sun in the Copper Basin and the inner part of Cook Inlet. And between the Alaska and Brooks Ranges there are wide sweeps of grassland, green with meltwater and the warmth of the sun, extending westward across what has been and will be the Bering Sea to Siberia, then sweeping onward thousands of miles to the back of the European ice sheets. Only an occasional mountain range carries an ice cap there, but areas of tan and gray are visible even from space -- dust storms, sand dunes, and plains of silt and gravel dropped by the meltwaters from the glaciers. North of the ice-capped Brooks Range, the cracks that opened in the chill of last winter filled with drifting sand, rather than snow.
As you move into the Fairbanks area for a landing, you startle a small herd of shaggy ponies into headlong flight, and a few moments later a group of bison stampedes as well. Their small hooves, designed for speed on hard ground, are only slightly impeded by the moisture still oozing from the few remaining patches of snow. This is mineral soil, blooming with grasses, sedges, sagebrush and wildflowers in the spring flush of moisture, not muskeg.
The trumpet of a startled mammoth splits the air from the line of willows and taller grasses along the river, and a family of the huge, long-haired animals moves into view. They are edgy, and with good reason -- a saber-toothed tiger has had its eye on the new calves for several days now.
Eighteen thousand years ago is an extreme case, near the height of the last ice age. But if you picked a random time in the last half million years, it would likely be closer to the icy picture I've just described than to the world we are familiar with today. Less than ten percent of this period has been as warm as the last few thousand years, or with as little ice on the land. Exact dating prior to about thirty-five thousand years ago (the limit of accurate radiocarbon dating) is still a problem, but many lines of evidence suggest a long series of ice ages, separated by relatively warm interglacials around ten thousand years long and close to a hundred thousand years apart. Our current interglacial has lasted a bit more than ten thousand years. Are we due for another ice age?
Since the glaciers of Antarctica, Greenland, the Canadian Arctic, and the mountain glaciers of modern Alaska together account for a third of the total area of the great ice sheets of the glacial maximum, we could argue that we are still in an ice age -- that even what we think of as interglacials are in fact mere pauses in an ice age that has lasted for well over a million years.
Whether we label our era a minimal ice age or a true interglacial, our present civilizations are in balance with the climate. Consider: sea level rose over three hundred feet in the last twenty thousand years, drowning what was once dry land. Vast areas of the Bering and Chukchi seas, for instance, were steppes and cold deserts when the water that now covers them was locked up in glacial ice. Much of our concern about the onset of a "greenhouse" warming comes from the possibility that parts of the remaining land ice could melt, causing a further rise in sea level. If that should happen, shoreside cities -- Homer and Honolulu, Nome and New York -- might go the way of the Bering land bridge. Ice ages are by no means a problem only of the past.
