What if 12 asteroids were on collision courses with earth? What if we could alter their trajectories and save our planet by the cumulative effect of our individual efforts? What if science and history proved that we were fully capable of such heroism? What would it take to get us started?

John Schellnhuber, distinguished science advisor at the Tyndall Centre for Climate Change Research in the United Kingdom, has identified 12 global warming tipping points, such as the deforestation of the Amazon rainforest or the melting of the west Antarctic ice sheet. Any of these, if triggered, will likely initiate sudden changes across the planet, as cataclysmic as any asteroid strike. So what will it take to trigger what we might call the 13th tipping point, the shift from personal denial to personal responsibility? What will tip us toward addressing global warming with the urgency it deserves, as the mother of all threats to homeland security?

A 2005 study on Americans' perceptions of global warming found that most are moderately concerned, but 68 percent believe the greatest threats are to people far away or to nonhuman nature -- a dangerous and delusional misperception. Only 13 percent perceive risk to themselves, their families or their communities.

Many secretly perceive global warming to be an insoluble problem and respond by circling the family wagons and turning inward. Yet science shows that human beings are born with powerful tools for solving this quandary. We have the genetic smarts and the cultural smarts. We have the technological know-how. We even have the inclination.

The truth is we can change ourselves with breathtaking speed, sculpting even "immutable" human nature. Forty years ago many believed human nature mandated that blacks and whites live in segregation; 30 years ago human nature divided men and women into separate economies; 20 years ago human nature prevented us from defusing a global nuclear standoff, but in 1987 the U.S. and Soviet Union signed the INF agreement. Nowadays we blame human nature for the insolvable hazards of global warming.

Research out of the Max Planck Institute in Germany suggests how we might help ourselves evolve. We behave as better environmental citizens when educated about the science of global warming, and when our individual actions are visible to those around us -- a phenomenon known as "social facilitation." Perhaps if we're vigorously informed of how global warming endangers our neighborhoods, we'll individually forego the McMansions and the Hummers and make other sustainable choices. Anything less compromises our children's future.

Until then, our denial facilitates "social loafing": the tendency of individuals to slack when work is shared and individual performance is not assessed. There's no better example than the U.S. Congress, where members cloak their lethargy regarding global warming behind the stultifying inactivity of their fellows. And why not? After all, who's watching?

Not the media, which habitually squelch new science stories on global warming by rationalizing that we've heard that before , though they would never ignore another round of Middle East bloodletting. The growing body of scientific knowledge on climate change gains heft and power as it accumulates, but the public rarely hears about it, reinforcing our loafing.

Scientists don't help when they react to the terrifying dimensions of public ignorance by sheltering inside hallowed halls. At a recent meeting of the Society for Conservation Biology, 70 percent of members argued in favor of advocating real solutions to environmental problems directly to lethargic policymakers and the press. Yet most researchers remain sequestered at a time when we need their knowledge and expertise like never before.

The nature of tipping points is that they happen dizzyingly fast. The good news is that history proves we're capable of keeping up. Social scientists once believed it would take decades of government pressure and education for Americans to choose smaller families, since the desire to procreate is an absolute part of the human animal, or so they thought. Yet population growth radically declined over only three years in the 1970s -- one woman at a time -- without an ounce of government involvement.

Political leaders can help. But even without them we can help ourselves. Whether or not Marie Antoinette actually said, "Let them eat cake," she inspired change that reverberated far beyond Europe. Likewise, when George W. Bush says we can't act on global warming until we "fully understand the nature of the problem," we can use his callous disregard as a rallying cry.

The truth is, humans can change, and change fast. Our hallmark is adaptability. Long ago, we looked out from the trees and saw the savannas. Beyond the savannas we glimpsed further frontiers. History proves that when we behold a better world, we move toward it -- one person at a time -- leaving behind what no longer works. We know what to do. We know how to do it. We know the timeline. We are our own tipping point.

This piece is adapted from a longer article in the current issue of Mother Jones.

Julia Whitty is a contributing writer for Mother Jones and the author of the forthcoming book The Fragile Edge: Diving and Other Adventures in the South Pacific.