IF an event could be pinpointed that opened the present chapter of environmentalism in the United States, it was on June 22, 1988 - early in one of the hottest, driest summers on record. NASA scientist James Hansen testified that day before a Senate subcommittee that the Earth's climate was already growing warmer, that the fumes of modern civilization trapping heat in the atmosphere were the probable cause, and that hotter, drier summers were in store.
With the searing weather as a dramatic backdrop, Dr. Hansen's words gave the term ``greenhouse effect'' a new respectability in the news media.
In the following months, the cosmic notion of global warming became familiar to people who merely watched the evening news or read newspapers or magazines.
In the late 1980s, public concern over the environment rose like a tidal surge across the Western world. The mood at the brink of the 1990s - to environmental activists, lawyers, and researchers - is strikingly like that of the brink of the 1970s.
But the environmentalism of today is far more worldwide than on Earth Day, 1970. In America, concerns are at once more global and more personal - from the hole in the ozone to radon in the basement.
Some pivotal events helped shape current consciousness:
The Exxon Valdez oil spill off Alaska last spring; the Soviet nuclear plant accident at Chernobyl in 1986; the catastrophic leak of poison gas at a Union Carbide plant in Bhopal, India; and the 1985 discovery of an expanding hole in the ozone layer of the atmosphere over Antarctica.
The hole in the Earth's ozone led to what was probably the largest political action of the decade concerning the environment - the Montreal Protocol, an international accord for phasing out the use of chlorofluorocarbons (CFCs) that deplete the ozone.
But the 1980s were not a decade of political action, but rather of the strengthening of environmentalism's roots in public sentiment.
The hole in the ozone also brought home the remoteness and unpredictability of mankind's effect on nature. It worried people, says Lester Brown, president of Worldwatch International.
Unlike dirty rivers and brown skies, ``It was something they couldn't get their hands on,'' he says.
Democratic pollster Celinda Lake has seen a growing ``sense of clear and present danger'' in Americans on both global and local matters of the environment.
Last spring and summer, she watched concern increase over ozone and CFCs. Why? Television coverage, mostly, and articles like one in Parade magazine on a woman fighting CFC emissions in her own kitchen.
``I must have heard about that woman in focus groups a hundred times,'' says Ms. Lake.
This fall, Lake found in New Jersey that three out of four residents were seriously concerned that their houses might rest on or near a toxic dump.
``It could be that everyone has his own oil-spill-type experience,'' says Fred Anderson, an American University law professor and founder of the Environmental Law Institute.
The shift in opinion has been fairly clear-cut. In the fall of 1987, 32 percent of Americans believed that the environment was worse than five years earlier, while 41 percent believed it was better. A year later, 46 percent thought it was worse and 32 percent better, according to Cambridge Reports surveys. Other polls show variations of the same trend.
The environmentalism of today is much better established than it was during its first major wave of popularity. Concern over air and water pollution in 1988 was at least half again as widespread as it was in 1970, according to Gallup polls. And now concerns have spread to a wider range of issues.
The leap in the polls in 1988 was due to concerns over heat, drought, cracked mud across the bed of the Mississippi, used syringes washed up on Eastern beaches, dolphins dying mysteriously by the hundreds, burned-orange urban skies, blistered and deformed coastal fish and shellfish.
The weather may have had no relation to the greenhouse effect at all. But scientists like Hansen said such summers would be occurring more often in coming decades.
More important, such warnings moved off the science pages of the nation's agenda-setting newspapers and onto their front pages and the evening news. The summer offered television ideal visual shots to add a visceral sense of environmental crisis to reports of long-term problems.
To skeptics, the sense of crisis is due to environmentalist organizations themselves and their spreading of alarm. Oil spills and hot summers have been occurring for decades, says Richard Stroup, a senior associate at the Political Economy Research Center in Bozeman, Mont.
``The difference is that organizations have made a very successful business, for better and for worse, of trumpeting catastrophe theories,'' he says.
Dr. Stroup, and other conservatives such as Kent Jeffreys of the Heritage Foundation, do not deny environmental problems, but believe that few, if any, are at crisis levels, and that fear is leading to poor policy responses.
Part of what has happened in the 1980s is that Americans - as consumers, homeowners, parents - take less for granted about their environments.
Trust of regulators and institutions is giving way to an insistence on more information. Accidents such as the Bhopal catastrophe have put people on notice to make more of their own risk decisions, notes Bud Ward of the National Safety Council.
``The permissiveness and faith has been replaced with caution and cynicism,'' says Durwood Zaelke, director of the Center for International Environmental Law.
Another often cited cause of the greater environmental alertness of the late 1980s is the flagrant environmental laxness of the early Reagan administration.
``We almost have to look at the 1980s as the lost decade,'' says David Gardiner, a Sierra Club lobbyist.
A 1962 book, ``Silent Spring'' by Rachel Carson, stirred the American environmental movement to life. Its legal and bureaucratic structures were built in the 1970s, largely under Richard Nixon.
Two Reagan appointees - James Watt as secretary of the interior and Anne Burford Gorsuch as Environmental Protection Agency administrator - were so hostile to environmental regulation that they proved a fund-raising boon to environmental organizations.
But environmentalists now admit that Reagan's lack of interest in the environment reflected something in the American public.
James MacKenzie, a senior associate at the World Resources Institute who served on the White House Council on Environmental Quality in the Carter administration, says that the ``overzealousness in some respects of the Carter folks'' helped drain some concern from the public.
``Too much bad news,'' he explains. Carter ``was pretty gloomy.''