A 10-year, federally sponsored investigation is concluding that acid rain causes some significant environmental damage but far less than initially feared. "The sky is not falling, but there is a problem that needs addressing," James Mahoney, director of the National Acid Precipitation Program, said as about 700 scientists from around the world gathered here last week to examine and argue about the results of hundreds of studies that will form the basis for the program's final report to Congress.
"Acid rain does cause damage," Mahoney said, "but the amount of damage is less than we once thought, and it's much less than some of the characterizations we sometimes hear."
Some of the findings of the half-billion-dollar program are riddled with uncertainty. Some scientists, moreover, criticized the assessment as prematurely concluding that acid rain is causing little harm to American forests.
And Canadian scientists charged that the assessment understated the problem in their country, a problem to which, it is generally agreed, the United States greatly contributes.
But Mahoney said that while there is "a great deal of room, still, for debate and interpretation," the extremes of the debate _ the view that acid rain represented an imminent environmental disaster and the opposite view that it was not a problem _ have now been eliminated.
The federal research program, created by Congress in 1980 to provide the government with a definitive study of acid rain, has engaged the efforts of hundreds of scientists. These are among the major findings:
In the United States, fewer than 1,200 lakes have become fully acidified. Little can live in them, and acid rain is mostly responsible.
In the Northeast, where most of the concern has focused, those lakes that are going to become acidified have already done so.
Except for red spruce at high elevations in the Eastern mountains, there is no evidence that acid rain has caused a general decline of forests.
But a sizable minority of scientists argued the report had given short shrift to the possibility that over the long term, acid rain causes nutritional deficiencies in trees by altering soil chemistry.
There is no evidence that acid rain in the United States harms crops.
Acid rain and dry acid particles in the atmosphere could pose a health risk to asthmatics, people with heart or lung disease, children and the elderly. But the report said the health risk was speculative.
In broad perspective, say Mahoney and some others, acid rain cannot be seen as ranking even near the top of a present-day priority list of environmental issues that also includes urban air pollution, destruction of tropical forests, depletion of the ozone layer and the possibility of global climate change.
But some environmentalists disagreed, saying there are more reasons to be concerned about acid rain than there were 10 years ago.
Then, the concern focused on damage to lakes and streams in the Northeast. Now it involves lakes and streams in other regions as well, along with forests, human health, atmospheric visibility and damage to materials.