Volcano’s Fallout Tests Theories on Atmosphere

The eruption of Mt. Pinatubo in the Philippines last June pumped enough gas and debris into the upper atmosphere to create golden sunsets around the world for a couple of years, and it gave scientists a chance to test their pet theories concerning the thin envelope of air that surrounds the Earth.

If the Earth’s atmosphere works the way scientists think it does, then the eruption of Mt. Pinatubo should have predictable results. Mt. Pinatubo was the greatest volcanic eruption of this century, blasting 10 times as much material into the atmosphere as the 1980 eruption of Mt. St. Helens.

Scientists believe gases released by the volcano will eat away at the layer of ozone that protects the Earth from harmful ultraviolet solar radiation. Dust from the blast should cool the planet slightly and produce the golden sunsets that already are prominent.

But researchers who have presented their research over three days during the fall meeting of the American Geophysical Union are more concerned about whether the other predictions will come true. Much rides upon the outcome, including the validity of the warning that the Earth is gradually growing warmer because of the release of carbon dioxide from the burning of fossil fuels. Carbon dioxide is believed to trap solar radiation, and that should lead to a rise in temperatures.

However, dust from Mt. Pinatubo should also shade the Earth slightly, thus resulting in lower temperatures.

“Either we’re going to see substantial cooling over the next two years or our global climate models are wrong,” said James Hansen of the National Aeronautics and Space Administration’s Goddard Institute for Space Studies in New York.

He said the average global temperature should drop about one degree for about two years, more than enough to offset global warming.

Because the eruption was so recent, no effect has been measured yet, but Hansen said the next two years should tell whether scientists are right.

Scientists also expect gases released by Mt. Pinatubo to cause further depletion of the ozone layer, and there is some very preliminary evidence that they are right.

One team of scientists reported this week that while it is still too early to tell for sure, readings from their instruments taken just days before the meeting here indicated that ozone is, indeed, being eaten away by gases from the volcano.

The team uses radar to measure the amount of ozone in the upper atmosphere over Boulder, Colo., and in the last few weeks the amount of ozone has been decreasing, according to David J. Hofmann of the National Oceanic and Atmospheric Administration in Boulder.

Finally, on Dec. 6, just before he left Colorado to present his findings here, “we registered the lowest ozone count ever recorded over Boulder,” Hofmann said. “It (the recent results) suggests that the stage has been set for major ozone depletion this winter.”

Scientists are concerned over the problem because of a persistent hole in the ozone layer that forms each fall over Antarctica. That hole is believed to have been caused by the release of chemicals into the atmosphere from such things as coolants used in refrigerators.

The further depletion in ozone from Mt. Pinatubo is not life-threatening, but it could have some effects on humans, such as increasing the risk of skin cancer.