The bedrock of the environmental movement is scientific evidence about nature and how humans affect it. But science is typically incomplete. New tools, techniques, and questions can overturn yesterday's headline-making results - and policies built around them.
Where does that leave those who want a safe and clean environment?
Take the gasoline additive known as MTBE. To cut smog, it was put into about a third of the nation's motor fuel. Alas, an EPA-appointed panel now says that Methyl Tertiary Butyl Ether should be scrapped, citing the ease with which MTBE leaks into water supplies and studies indicating the compound's potential threat to health.
Because of incomplete research, an environmental solution later became an environmental problem. We should be careful, one government official warned, not to leap again at making profound changes in fuel supplies.
Another humbling, truth-comes-late example is a recent report by the Friends of the Earth that the biggest consumers of Brazil's Amazon forests are not in Europe, Japan, or America. They're in Brazil. A global effort to ban world trade in Amazon wood doesn't do much when Brazil uses 86 percent of its tropical timber production.
On a more planetary scale, climatologists now say greenhouse gases that help cause global warming are not accelerating but have actually declined about 25 percent since 1980.
It's not easy being an environmentalist these days. Three decades ago, humans just had to stop messing with Mother Nature. Eliminate DDT and the bald eagle returns. Clean up sewage and waterways are swimmable. Stop whaling and save the whales. And so on.
But the next steps in environmental quality are more complex. They take more careful research. Is there harm, for instance, in growing or eating genetically altered agricultural plants? Knee-jerk assumptions can't substitute for verifiable science.
Even more daunting is a trend in the 1990s - beyond not messing with Mother Nature - to recreate nature. Environmentalists want to bring back a "pristine" wilderness and put humans in "sustainable" harmony with nature.
All well and good. Wolves were reintroduced in the Northwest in 1995. Midwest prairies are being replanted. A dam was removed in Maine this spring, letting fish swim freely. And in the largest environmental restoration project ever proposed, the Everglades may be returned to a "natural" ecosystem after a half century of draining and canal building.
In such cases, science must become more predictive. Certainties are harder to come by. What is "pristine" wilderness after millenia of human impact on Earth and how do we calculate "sustainability"? The human role in nature still needs sorting out.
Let's not allow enthusiasm for protecting - or bringing back - nature get too far ahead of the science.
(c) Copyright 1999. The Christian Science Publishing Society