Dr. Suzuki, a zoologist turned environmental activist, has been sounding this alarm for years - in books, on television and radio, in newspaper columns and in coast-to-coast campaigns in his native Canada. He has "seeped into the minds of virtually every one of the 31 million Canadians," said Joseph R. Foy, campaign director for the Western Canada Wilderness Committee, a conservation group. "He is the environmental conscience of the people."
His effects reach beyond Canada. Dr. Eric S. Chivian, a psychiatrist who directs the Harvard center where Dr. Suzuki spoke last month, said he became "a Suzuki groupie" about 20 years ago when he heard him speak.
"Here was a senior scientist who had decided that the most important thing he could do with his career was to translate the abstract, technical language of science - especially the science of those issues that constituted the greatest threats to human life - into terms the average person could understand," Dr. Chivian said. "There are very few in the scientific world who have David's gift for doing this, and there are still fewer who communicate with such directness."
He appears routinely at or near the top of lists of the most admired, liked or influential Canadians. More than 150,000 people have signed up so far for the "David Suzuki Nature Challenge," promising to take the simple steps he recommends to lighten their collective footprint on the environment.
When the novelist Margaret Atwood won the 2000 Booker Prize, she said, she gave a "substantial portion" of the approximately $30,000 prize to the David Suzuki Foundation (www.davidsuzuki.org), which Dr. Suzuki established in 1989 to analyze and find environmental solutions.
And when Jean Chrétien, then the prime minister, signed Canada on to the Kyoto Protocol on greenhouse gases, he credited Dr. Suzuki and his foundation for building support among Canadians.
Kyoto was "a winning hand" for Mr. Chrétien because 80 percent of Canadians favored it, even in oil-producing areas, said David Anderson, who was Mr. Chrétien's environment minister. "David Suzuki was very important in that regard. He has clout, he has a strong following and he is a genuine scientist."
These days, Dr. Suzuki worries most about how people have become estranged from nature, habituated to seeing the world "through a fragmented lens," as he puts it, and oblivious to the fact that the economic abundance of the modern world depends on the health of its air, soil and water.
"Even though Canada has a lot of wilderness, 85 percent of us live in cities," he said. "We don't understand ecosystems."
He makes this point with anecdotes and examples anyone can understand. For example, he recalled, when he wanted to do a television program about air pollution, he waited for a smog alert day and took a film crew to a hospital emergency room. "It was packed with old people and children," he said. "What blew us away was how many of these people were being driven to the hospital in an S.U.V. Because they live in a shattered world, it never occurs to them that the way they live is creating the problem."
Dr. Suzuki said he used to urge people to think globally, act locally. "That was a mistake," he says today. "When people think globally, they feel helpless."
Instead, his Nature Challenge outlines 10 simple steps - like eating meatless meals one day a week or using nontoxic lawn products - and urges Canadians to commit to three of them.
He hopes a million Canadians will sign on. "If we can do that, we can get anyone in business and politics to sign on," he said. Some environmentalists resent the attention Dr. Suzuki receives and some scientists criticize him as having abandoned the purity of the laboratory for the hurly-burly of politics.
Others, citing the music he favors on his television program, his advocacy of Native American causes and his affection for whales, dismiss him as being too much in the New Age.
"There is a certain amount of sniffiness on the part of academic scientists who feel he is not as rigorous as he should be," said Mr. Anderson, who today represents Victoria, British Columbia, in Parliament.
But the sniffers are in the minority.
Dr. Suzuki's influence is more remarkable given his life story, which he recounted in 1987 in a memoir, "Metamorphosis" (Stoddart).
David Takayoshi Suzuki was born in 1936 in Vancouver, where his parents had a dry cleaning business.
But after the attack on Pearl Harbor, and even though his parents were native-born Canadians, the government confiscated most of the family property and shipped them off to a detention camp in a remote village in the Rocky Mountains, with other Japanese-Canadians.
Eventually, he recalled in an interview, they and other internees were offered a choice: leave Canada for Japan or resettle east of the Rockies. Affronted by their government's actions, most chose Japan; in their camp, Dr. Suzuki wrote, his family was the only one to choose Canada.
They moved to Ontario, where he went to high school and where outings with his father fueled his interest in nature. He filled his bedroom with fossils, insects, dead and live fish and snake skins, and stored collections of worms in the family refrigerator, where his mother would patiently remove escapees from the vegetable bin.
After high school, he won a scholarship to Amherst College in Massachusetts and then went on to graduate school at the University of Chicago, where he earned a doctorate in zoology in 1961, specializing in genetics. After a fellowship at Oak Ridge National Laboratory, he returned to Canada, to a teaching job at the University of Alberta.
At first, he seemed headed for a conventional career of research and teaching. His work on temperature sensitivity of genetic mutations in fruit flies was widely cited, and he is a co-author of a genetics textbook still in wide use. But already the direction of his life was changing.
One day, he was asked to appear on the university's television show, "Your University Speaks." "It was a very shoddy kind of television," he recalled. "We were paid $15 a show." But people liked his programs and he realized he had the knack of using them to explain complex scientific topics.
By 1971, after he moved back to Vancouver, to the University of British Columbia, he had his own program, "Suzuki on Science," on the CBC. His shoulder-length hair was held with a headband, he said. "The scientific community felt I had no business representing science."
But he did, in television and radio programs including a television series he inaugurated in 1974 that was first called "Science Magazine," then "The Nature of Things," and now "The Nature of Things with David Suzuki," seen in 30 countries. He has also done programs for the BBC and has appeared from time to time in the United States, in programs shown on PBS and on the Discovery network.
Though they do not do everything he wishes they would, Canadian politicians cannot ignore him, he said. "They know people watch my program."
Dr. Suzuki attributes his prominence in part to the fact that there are relatively few advocates for the environment who are also professional scientists. In the United States, he said, "there are a lot of eminent environmentalists, but they divide up" between people who are primarily academic researchers and those, mostly without advanced science training, who are activists.
Dr. Suzuki added that he was fortunate early in his career to receive fellowships that allowed him to continue his research while working in television.
He also said he thought that other scientists, over all, "basically have contempt for journalists and do not take communication seriously."
Dr. Suzuki, who lives with his second wife in Vancouver, retired from his university post in 2001 to concentrate on the foundation, his media efforts and his work on the United Nations Millennium Ecosystem Assessment, on whose board he serves.
His foundation's latest effort, Sustainability Within a Generation, recommends an array of government, business and individual efforts, none of them enormously painful and all of them on a timetable, that would greatly reduce Canadians' collective impact on the natural world.
And even though the marsh he explored as an adolescent is now a shopping mall, and he does not see too many signs of environmental progress, he is hopeful.
The challenge, he says, is "to put the world back together again, to think holistically, in geological time, not corporate time or political time."
This is not an impossible dream, he says in one of his videos, citing the end of the cold war and the abolition of apartheid as seemingly impossible dreams that came to pass and adding, "No one has the right to say what cannot be done."