NCPA - National Center for Policy Analysis

What is it Worth to Save the Earth?

November 13, 2003

"On an average night, more than 100 million pieces of interplanetary debris enter Earth's atmosphere," says Scientific American. Most vaporize in the atmosphere; larger rocks explode. Once a year, on average, the atmosphere is struck by rock that explodes with the force of a small nuclear weapon (4 to 5 kilotons).

We now know that the Earth has been repeatedly struck by larger rocks capable of serious damage. Would it be cost effective to take measures to protect ourselves from such potential devastation?

According to recent studies:

  • There is a .02 percent chance that the Earth will be struck in this century by asteroid more than a kilometer across -- the equivalent of 100,000 megatons of TNT and capable of wiping out humanity.
  • There is a 2 percent chance that the Earth will be hit before 2100 with a rock more than 100 meters across -- equivalent to 100 megatons of TNT and capable of killing many millions.
  • There is a 10 percent chance of the Earth being hit this century by a rock roughly 60 meters across -- equivalent to 10 megatons and capable of destroying a city the size of New York; one like it flattened 2,000 square miles of forest in Siberia in 1908.

Averaged out over time, several thousand people a year will die from such impacts. If we value their lives at just $1 million a piece, an expenditure of several billion dollars each year would be justified to prevent such an occurrence.

About $10 million a year is now being spent on space surveys to identify and track asteroids with Earth-crossing orbits. One team of scientists and astronauts has proposed a $1 billion program over 10 years to develop a space tug that could nudge an asteroid out of the way.

Source: Russell L. Schweickart et al., "The Asteroid Tugboat," and Editorial, "Penny-Wise, Planet-Foolish," both Scientific American, November 2003.


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