Experts debate just what is the source of global warming trend. Ozone hole and climate changes may be related to sunspot activity
Boston — Scientists concerned with the climatic impact of chemical pollution continue to have trouble linking cause and effect. They suspect that certain chemicals, such as fluorocarbons used as spray-can propellants and refrigerants, are depleting Earth's protective ozone layer. Now a new study suggests that the sun is involved.
Climatologists also expect the buildup of carbon dioxide and other heat-trapping gases in the air to warm our planet. According to a newly reported study, the permafrost along Alaska's North Slope has warmed considerably. This could be an early sign of carbon dioxide heating. But the climatic situation is so complex that experts are reluctant to draw this conclusion.
The ozone layer is important because it filters out harmful solar ultraviolet light. Ozone itself is a form of oxygen with three atoms per molecule. It is regularly made by the action of sunshine on the upper atmosphere and just as regularly destroyed by natural chemical processes there.
Chemical pollution could tip the balance in favor of destruction. This could account for ozone losses that have been reported.
However, Linwood B. Callis of the National Aeronautics and Space Administration's Langley Research Center, and Murali Natarajan of SASC Technologies in Hampton, Va., put the blame for at least some of the ozone depeletion on the recent upswing of the roughly 11-year sunspot cycle. It peaked in 1979 and early 1980.
The researchers explain in the current issue of Science magazine that this rise in solar activity boosted nitrogen dioxide concentrations in the stratosphere up to 75 percent between 1979 and 1984.
That, in turn, led to increases in concentrations of other ozone-destroying chemicals. These could account for the slight general decline in the ozone shield that has been observed, and even for the notorious Antarctic ozone hole, the two scientists say.
The loss of Antarctic ozone was so pronounced that the National Oceanic and Atmospheric Administration (NOAA) sent a special expedition to the frozen continent to study it.
Reporting the results at an Oct. 20 press conference, expedition leader Susan Solomon said her team could not ``conclusively establish the cause'' of the ozone loss. But she ruled out solar activity. She considered the likely culprits to be man-made chemicals.
At the time, Mr. Callis insisted that it was premature to discount the sun. Now he and Dr. Natarajan have presented a satellite-based study that supports the idea that solar activity can deplete stratospheric ozone.
With that activity now on the wane, the ozone layer may begin to recover, Callis says.
He observes that, if he and Natarajan are correct, ``this will be the first indication that a solar cycle can have such a major effect on the atmosphere.''
Meanwhile, strong warming of the permafrost on Alaska's North Slope may be the clearest sign yet of the anticipated carbon dioxide effect.
Arthur M. Lachrenbruch and B.Vaughn Marshall of the US Geological Survey report that North Slope permafrost temperatures have risen 4 to 7 degrees F. during the past century, depending on location. Their study, published in the current issue of Nature magazine, includes measurements made in two dozen old oil exploration wells that were drilled since the 1950s.
This correlates with a 1-to-1.5 degree general atmospheric warming over the same time period. This warming is even stronger in the Arctic, where it runs roughly 3 to 5 degrees.
J.Murray Mitchell Jr., senior research climatologist with NOAA, has studied global temperature changes extensively. He acknowledges that the permafrost warming ``is consistent with the idea that it might be the [carbon dioxide] effect.'' However, he warns against jumping to any climatic conclusion at this time.
Mr. Mitchell points out that periods of climatic warming and cooling are nothing new. Moreover, he says, the permafrost warming is only ``circumstantial evidence.'' That warming and the warming of the atmosphere could be due to other influences. The possibilities include fluctuations in solar activity, volcanic dust, and poorly known heat exchanges between the air and the sea.
Then, as Dr. Solomon observed in connection with the ozone hole, the climatic factors ``may well be something not yet thought of.''