Our political leaders don't win every debate, but they have a huge influence on what we debate. Leadership requires that one be able to tell the difference between what is urgent and what is important and to gauge magnitude. Leaders should help educate us on important issues. They should encourage civic discourse, debate, and action on these important issues. And the scale of the action must fit the magnitude of the problem.

The issue of global warming is proof that a vacuum exists precisely where leadership is most needed. The existence of human-induced climate change should be beyond fundamental debate. The science is clear. The trends are alarming. The implications are profoundly threatening to the status quo. We are looking at a world that by midcentury will be significantly warmer and different in ways we can only guess.

John Holdren, the incoming president of the American Association for the Advancement of Science and an energy specialist from the Kennedy School and the Woods Hole Research Center, has said that the 5-7 degree change predicted from a doubling of greenhouse gases by 2050 may be a best-case scenario. We are headed for a quadrupling of these gases, which would lead to a 20-degree change by midcentury. He calls this a ''roasted world."

James Hansen, director of NASA's Goddard Institute for Space Studies, has said if we are not operating very differently within 10 years, this change will be irreversible. Other scientists do not give us that much time.

But temperature change is only one effect. Rising sea levels, from thermal expansion and melting ice caps, is another. Major shifts in thermohaline circulation, such as the Gulf Stream, because of increasing amounts of fresh water off of Iceland, could change the climate in Europe within a generation.

It has happened before. These are changes many people think they can escape by moving. We simply don't grasp the size of the problem.

Rising temperatures lead to more evaporation and more energy in the atmosphere, leading to more severe weather. Katrina's impact was felt far beyond Mississippi and Louisiana. Katrina turned part of the United States into a Third World country in a matter of hours.

It will cost the federal government $75 billion that we don't have. How many Katrinas would it take to bankrupt the country? To finish off the insurance industry? To cause massive human dislocation? To overwhelm health and shelter providers? Why would we think that this can't happen to us?

There are those who see our planet not as fragile, but strong. They see earth as a sustainable, developing, self-correcting organism that has existed for more than 10 billion years. Looking at earth this way, one realizes that humans have been part of this system for only 4 million of those years. Right now, human beings may be the only species whose elimination would benefit all other species. Are we immune from this correction? Why would we think so? This isn't about saving the earth. The earth will do a fine job of saving itself. This is about us.

Right now we are showing (and our leaders exemplify) characteristics that, in combination, are toxic. We have believed since Genesis that we are apart from nature and our job is to achieve dominion over the earth. We believe we are in control of the earth. What hubris. We are largely ignorant of science, and we hope what we don't know can't hurt us. And lastly, we live in denial. This issue of the changing climate isn't really that big a deal. Arrogance, ignorance, and denial -- that is a fatal combination.

What we need from our leaders is the opposite. We need them to know that there is no more important issue than reducing greenhouse gas emissions. We need a proper sense of perspective. This isn't just about Cape Wind. This is about more Cape Winds, everywhere we can put them. This is about nuclear power because the risks from long-term storage of nuclear fuel rods pales in comparison with the harm being caused right now.

In the past, leaders have mobilized actions that have changed the course of the world. But a melting glacier doesn't have the political impact of Pearl Harbor or a Soviet sputnik. So today's leaders don't see the magnitude of the threat.

My granddaughter is 18 months old. This issue will change her life. What will I say to her? We can respond to this crisis. Many of us are willing to play a role, to change our behavior. We need to believe that our individual actions will be combined with others to change the course of human events. That's why we need leaders. But we need leaders who have the intelligence to see climate change for what it is -- a crisis. We need leaders who realize we are not guaranteed an existence. And that we need to act now, not only for future generations, but for ourselves.

John K. Bullard, the former mayor of New Bedford, is president of the Sea Education Association. He directed the NOAA's Office of Sustainable Development in the Clinton administration.

© 2006 The Boston Globe

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