Gordon McBean drove to Meech Lake, Que., in the summer of 2002 to brief the federal cabinet on global warming.
The Liberals were holding a retreat to debate whether to ratify the Kyoto agreement on climate change. Dr. McBean, one of Canada's top climatologists, told them Kyoto was only the first step, and they would have to make much deeper cuts in greenhouse-gas emissions by 2050.
A hotter world could mean surging sea levels, more frequent violent storms, severe heat waves and droughts, but it would be decades, Dr. McBean told them, before the benefits of cutting emissions would be seen.
One minister -- Dr. McBean won't say who -- seemed appalled.
"And there will be nothing for us between now and the next election?" the minister asked. "Why would we do this?"
Dr. McBean had a guilt-inducing answer ready. "You do it for your grandchildren," he said.
He wouldn't have marshalled this kind of emotional argument earlier in his career, when he was a senior scientist and bureaucrat with Environment Canada. Then, he felt strongly that researchers -- especially those working for the government -- could explain the science of global warming, but not push a course of action.
But by 2002, Dr. McBean had crossed that self-imposed boundary and become an advocate, one of a growing number of scientists whose warnings about the dangers of global warming have become more passionate -- and more personal.
Is it a good thing that they are sticking their necks out, talking publicly about what they see happening and what needs to be done? After all, their work is the foundation for political action on global warming, both in Canada and internationally. Or are they going too far, becoming climate crusaders instead of objective analysts and observers?
Many scientists don't see themselves as advocates, said David Runnalls, president of the International Institute for Sustainable Development. They believe it is their job to warn the world about global warming, he said, just as experts in infectious diseases warn us to get ready for an avian flu pandemic, or atomic scientists warn of the dangers of nuclear holocaust.
They are getting scared by what they are seeing, Mr. Runnalls said, such as the study published last year that suggested Greenland's massive ice sheet is melting faster than expected. "That is why a lot of them are far more outspoken than before," he said.
Dr. McBean, 63, said a number of factors pushed him into advocacy, including the increasingly compelling evidence of the dangers of climate change. He had moved to an academic position at the University of Western Ontario, so he felt more freedom to speak his mind.
He also did it for grandchildren, Amanda, 7, and Stuart, 10. He worried about their future in a warmer world.
So he speaks to church groups, naturalist clubs -- anyone who invites him -- and gives frequent interviews to the media in which he insists that governments must move now. Global warming is an issue of international and intergenerational equity, he says. It is future generations, particularly in the Third World, who will be hit hardest if the rich countries like Canada and the United States refuse to curb emissions. Island nations such as the Polynesian country of Tuvalu could be swamped by rising waves.
"We are talking about whole countries of people who have never had the benefits of burning greenhouse gases basically disappearing."
Burning fossil fuels such as oil, coal and gas keeps our houses warm in winter and our cars on the road. But it also produces carbon dioxide, one of several gases that trap heat in the atmosphere. C02 levels have been steadily building since the industrial revolution. In the late 1980s, scientists started warning that we may be altering the climate in ways that could have serious future consequences.
Those warnings are becoming more dramatic -- and, according to some critics, far more apocalyptic than is warranted by the science.
Perhaps it is the bureaucrat in him, but Dr. McBean is conservative in his language, compared with some of his colleagues, including Andrew Weaver, a professor at the School of Earth and Ocean Sciences at the University of Victoria.