by Bill McKibben

In my last column [1] for the magazine I wrote about numbers. Now I'd like for us to do some math.

Let's assume, generously, that 5 percent of Americans are deeply concerned about climate change- concerned enough that they will change all their light bulbs, scrimp and save to put a solar thermal hot water system on the roof (or really scrimp and save to put some photovoltaic electricity up there), unplug all their vampire appliances when not in use, cut the number of car trips that they make in half and use a hybrid for the remaining journeys, buy only local food in season, use a clothesline to dry their clothes whenever the temperature tops fifty degrees (1,016 pounds of carbon saved right there), cut their air travel by two-thirds and learn to enjoy the pleasure of "staycations," take showers with an egg timer so they don't stay under too long (350 pounds of carbon), and do all the other things that every website recommends for reducing your carbon footprint. And then let's assume that they go buy offsets for the rest from a company like NativeEnergy, which will use the money to build windmills on Indian reservations.

Okay, add it up, carry the one, dum de dum, here we go, yes-the impact on the amount of carbon in the atmosphere is, hmm, zero. Okay, not precisely zero. Every bit helps. But if your concern is somehow slowing the onrush of global warming in the short window of time the scientists give us, then the number is close enough to zero that it gives you pause. Even if that 5 percent then hector their in-laws, each of whom somewhat grudgingly does half of what they could, the net effect is still, well, right around zero.

I mean, the head of the Intergovernmental Panel on Climate Change, Rajendra Pachauri, said recently, "If there's no action before 2012, that's too late." By "action" he did not mean going down in the basement and adjusting the knob on your water heater to no higher than 120 degrees Fahrenheit. James Hansen, our premier climatologist, recently said that "if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm." It is true that if you clean the coils beneath your refrigerator it will run more efficiently, and it is also true that it won't do anything to "preserve a planet similar to that on which civilization developed and to which life on Earth is adapted."

I am exaggerating here to make a point. Of course I believe in energy conservation. I've got a plaque that says I built the most energy-efficient house in Vermont, I drove the first hybrid Honda Civic in the state, I subsist mostly on food from my Champlain Valley. I'm typing this article with electrons currently assembling themselves on my roof. All these things are good. I highly support them. Please do them too.

But in a world where we need massive change at lightning speed, the usual equations are turned upside down. We're used to thinking that being practical is what really counts-that you can only reduce carbon by, in fact, reducing carbon. Hence the light bulb, or the farmers' market, or the hybrid car. If we think globally, to use the hoariest of green clichés, we should act locally. In the fight against global warming, though, the practical acts are for the most part symbolic, while the symbolic acts might just save the day. Say you have a certain amount of time and money with which to make change-call it x, since that is what we mathematicians call things. The trick is to increase that x by multiplication, not addition. The trick is to take that 5 percent of people who really care and make them count for far more than 5 percent. And the trick to that is democracy.

We naïvely believe that it takes 51 percent of the people to make change in a democracy, but it clearly doesn't-5 percent is plenty, if those 5 percent are engaged in symbolic action that can force the kind of legislative change that resets the course for everyone. In the civil rights movement, for instance, the strategy was not to desegregate the country one lunch counter at a time-there were way too many lunch counters. Instead, you use the drama of the fight over one lunch counter to help drive the Civil Rights Act, which puts the full power of the federal government behind the idea that anyone can order a hamburger wherever they want to. And here's the thing: I bet less than one-quarter of 1 percent of Americans took part in a protest during that great movement, but it was more than enough.

If people who care about climate change mobilize politically, 5 percent will be more than enough too-it will persuade senators, congressmen, and presidents to back strict legislation that will set real caps on emissions and fund real research on the technologies we need. If such laws pass, they would change the behavior of 95 percent of Americans, including reluctant in-laws. This kind of equation isn't hypothetical. Two years ago, I helped organize a march across Vermont that called on our leaders to work for deep cuts in carbon emissions. A thousand of us walked the sixty-mile route-one Vermonter in six hundred. And yet that was enough to get all of our legislators, including the conservative Republicans, to sign on to our pledge. A year later we organized fourteen hundred demonstrations in all fifty states to call for 80 percent cuts in carbon emissions by 2050. They were the most widespread rallies about climate change to date, but even so they hardly reached one-quarter of 1 percent of the population. And yet the next week both Barack Obama and Hillary Clinton put our goal at the heart of their platforms.

So here's the thing. Along with spending a lot of time figuring out how to make your own life practically green (because, it's true, how are you going to face your kids if you don't?), spend at least a little time figuring out how to engage in the symbolic political action that might actually add up to something useful. In the United States check out 1sky.org and wecansolveit.org; since you're a citizen of the globe as well, you also need to help us at 350.org. Putting up a clothesline is a fine idea: 1,016 pounds of carbon, remember. But if you join Project Laundry List to fight for the idea of clotheslines, you become, in essence, an Amway salesman for positive change. Yes, your Prius definitively rocks-but even if you can't afford a Prius, you can accomplish considerably more by joining Al Gore's campaign to push for the rapid conversion to renewable electricity, which can power the next generation of hybrid cars.

It's not, I warn you, as immediately satisfying as installing a new tankless water heater or greasing the chain on your bike. You have to keep reminding yourself: multiplication, not addition. You have to keep reminding yourself that atmospheric physics and chemistry don't give you points for doing the right thing-they only care about how much carbon is in the atmosphere. We have so little time that we can't waste any of it. Screw in a new light bulb? Sure. Screw in a new global treaty? Now we're talking.