A New Doomsday?

Throughout history, prophets of doomsday have compiled a notoriously bad record. Now two scientists, influenced more by precise data than by intuition, have picked a date when life on earth may be seriously threatened if not doomed. By A.D. 3991, they say, the earth's magnetic field may have substantially disappeared. The result, some scientists think, could be catastrophic mutation of plant and animal life and widespread climatic changes.

Using magnetic-field data ranging back to A.D. 1670, Physicist Keith McDonald of the Environmental Science Services Administration and Robert Gunst of the U.S. Coast and Geodetic Survey have calculated that the field's strength has decreased by 15% in the past three centuries. If the decline continues at the present rate, they believe, the magnetic field will fade away completely in 2,023 years.

For 500 years before A.D. 3991 and for as long as 2,000 years afterward, the scientists estimate, the field will be so weak that it will not trap high-velocity electrons and protons streaming toward the earth from the sun. Instead of being confined by the magnetic lines of force to the Van Allen radiation belt, many of these particles will penetrate the atmosphere and strike the surface of the earth--causing an increase in mutation rates at best, eradicating entire species of animals and plants at worst.

Pole Switch. Even if the atmosphere absorbs most of the particles before they strike the earth, McDonald and Gunst suggest, there could be major climatic changes. During periods of intense solar bombardment, there are noticeable changes in atmospheric pressure and the direction of jet streams near the north and south poles, which are not protected by the magnetic field. Such changes on a worldwide basis, the scientists say, might cause lush valleys to become barren wastes, deserts to bloom, icecaps to grow and cover the land, or to melt and raise sea levels enough to flood coastal cities.

The earth is no stranger to disappearances of the magnetic field. Perhaps nine times in the past 4,000,000 years, geologic evidence shows, the field has mysteriously reversed. During these reversals the strength of the field gradually wanes, reaches a minimum, and then begins building up again in the opposite direction, resulting in a switch of the north and south magnetic poles. Exactly what will happen this time, McDonald and Gunst are not prepared to say. In the 700,000 years since the last reversal, most of the direct evidence of physical and biological changes that may have occurred in the absence of a magnetic field has been obscured by the passage of time.

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