What Caused the Cold?

Scientists have learned much about the great glaciers of the Pleistocene epoch--the slow ice masses that spread several times across much of the globe, killing off thousands of animal species and stimulating the evolution of man.

But what caused the periodic cold? There is no evidence that the sun has any cyclic activity that might have brought it on, nor can it be blamed on any other astronomical effect.

Explanatory theories have never been wholly convincing, but scientists keep trying. Now, in the magazine Na ture, Dr. Alexander T. Wilson of New Zealand's Victoria University of Wellington offers an intriguing solution. His reasoning points to Antarctica.

Floating Shelf. Unlike the northern polar region, which is ocean covered with ice, the area around the South Pole is a large land mass above which a thick icecap can form. During relatively nonglaciated periods such as the present, Dr. Wilson calculates, ice builds up on Antarctica, and the southern icecap reaches higher and higher. The top of the ice remains very cold, but the bot om is warmed slightly by heat escaping from the interior of the earth. Finally, the combined effect of pressure from the thickening cap and geothermal warming below melts the ice at the bottom. This frees the polar icecap from friction with underlying rock. It begins to spread out over the surrounding ocean as a floating ice shelf.

At its maximum, figures Dr. Wilson, the ice shelf covers 10 million square miles of ocean, and its white surface reflects so much sunlight that the earth's heat input is reduced by 4%. The earth's general temperature falls a few critical degrees, and ice sheets begin to grow larger in the Northern Hemisphere too. The bigger they get, the more solar energy they reflect back into space, and the colder the earth becomes.

Nibbling Ocean. This is what happened about a million years ago at the beginning of the Pleistocene, and the earth might have remained forever in perpetual deep freeze if not for a hid den weakness of the Antarctic icecap. As the ice spread out over the southern ocean, colder ice came in contact once more with the rock below it, freezing the slippery water layer between ice and rock (see diagram). This was the turning point. Held fast to the rock, the ice stopped moving. The ice shelf was nibbled away by the ocean, and the earth could capture more of the sun's heat. The earth's temperature rose again, and the glaciers retreated.

Dr. Wilson believes that this has happened several times and that the cycles of warmth and cold will continue until some movement of the earth's crust shifts the Antarctic continent away from the freezing temperatures of the South Pole. Just how soon the glaciers will spread out again over the Northern Hemisphere, he does not say.

This file is automatically generated by a robot program, so reader's discretion is required.