Before the Industrial Revolution the Earth’s atmosphere contained about 280 parts per million of carbon dioxide. The molecular structure of carbon dioxide traps heat near the planet’s surface that would otherwise radiate back out to space. There was a global average temperature of about 57 degrees Fahrenheit. Once we started to burn coal and gas to power our lives, that 280 number started to rise. During the 1950s scientific measurements discovered it had already reached the 315 level. Now it's at 380 and increasing by roughly two parts per million annually. The extra heat that CO_² traps, a couple of watts per square meter of the Earth’s surface, is enough to warm the planet considerably. We’ve raised the temperature more then a degree Fahrenheit already. It’s impossible to precisely predict the consequences of any further increase in CO_². But the warming we’ve seen so far has started to melt almost everything frozen on Earth; it has changed seasons and rainfall patterns; it has set the seas to rise.  

Our responsibility is to contain the damage, to keep things from getting out of control. The past couple of years have seen a series of reports indicating that 450 parts per million CO_² is a threshold we’d be wise to respect. Beyond that point, scientists believe future centuries will likely face the melting of the Greenland and West Antarctic ice sheets and a subsequent rise in sea level of giant proportions. Four hundred fifty parts per million is still a best guess. If concentrations keep increasing by two parts per million per year, we’re only three and half decades away from meltdown.  

U.S. carbon emissions continue to rise. China and India are suddenly starting to produce huge quantities of C0_². On a per capita basis they aren’t anywhere near to American figures but their populations are so huge, and their economic growth so rapid, that they make the prospect of a worldwide decline in emissions seem much more daunting. The Chinese are currently building a coal-fired power plant every week or so.  

To avert catastrophe there have to be rapid, sustained and dramatic cuts in emissions by the technologically advanced countries, coupled with large-scale technology transfers to China, India and the rest of the developing world so they can power up their emerging economies without burning up their coal.  

Three years ago a Princeton team made one of the best assessments of the possibilities. Stephen Pacula and Robert Socolow published a paper in ‘Science’ detailing 15 ‘stabilization wedges’ – changes big enough to matter and for which the technology was already available.  

1. Fuel efficient cars
2. Better-built homes
3. Wind turbines
4. Biofuels like ethanol
5. Building coal-fired power plants that can separate carbon exhaust so it can be 'sequestered’ underground  

All these approaches are more difficult then simply burning fossil fuel. We have already had our magic fuel and what comes next will be more expensive and more difficult. The price tag for global transition will be in the trillions of dollars. It will create myriad new jobs and when it’s complete it may be a much more elegant system. Once you’ve built the wind turbines the wind is free, you don’t need to guard it against terrorists or build a massive army to control it. If we replaced every incandescent bulb that burned out in the next decade any place in the world with a compact fluorescent we’d make an impressive start on one of the 15 ‘wedges’. 

We would need to build 400,000 large wind turbines. We would need to follow the lead of Germany and Japan in seriously subsidizing rooftop solar panels; we’d need to get most of the world’s farmers ploughing their fields less, to build back the carbon their soils have lost.  We’d need to do everything at once.  

Not all the answers are technological.  Many of the paths to stabilization run straight through our daily lives. They could demand difficult changes. Air travel is one of the fastest growing sources of carbon emissions around the world.  Many of us who are happy to change our light bulbs and drive hybrid cars chafe at the thought of not jetting around the world. What about take-away food?  According to one US study the average bite of food has travelled nearly 1,500 miles before it reaches an American’s lips, which means it’s been marinaded in (crude) oil.

We drive alone, because it’s more convenient than adjusting our schedules for public transit. We build ever bigger houses even as our family sizes shrink. We watch ever bigger TVs. Changes will occur as fossils fuels cost more. If what we paid for a gallon of gas reflected even a portion of its huge environmental cost, we’d be driving small cars to the train station. We’d be riding bikes when the sun shone. The most straightforward way to raise the price would be a tax on carbon.  But that’s not easy.  Since everyone needs to use fuel, it would be regressive – we would have to work out how to keep from hurting people unduly.

Earlier this a UN panel estimated that the total cost for a global energy transition would be just 0.1 percent of the world’s economy each year for the next quarter century.  A small price to pay.  

Global warming presents the greatest challenge we humans have yet faced.  Are we ready to change in dramatic and prolonged ways, in order to offer a workable future to subsequent generations and diverse forms of life? If we are, new technologies and new habits offer some promise. But only if we move quickly and decisively – and with a maturity we’ve rarely shown as a society or a species. It’s our coming-of-age moment, and there are no certainties or guarantees.  Only a window of possibility, closing fast, but still ajar enough to let in some hope.    

About Bill McKibben

Bill McKibben is an American environmentalist and writer who frequently writes about global warming, alternative energy, and the risks associated with human genetic engineering. Beginning in the summer of 2006, he led the organisation of the largest demonstrations against global warming in American history. McKibben is active in the Methodist Church, and his writing sometimes has a spiritual bent.  His first book, The End of Nature, was published in 1989 by Random House after being serialized in the New Yorker. It is regarded as the first book for a general audience about climate change, and has been printed in more than 20 languages. Several editions have come out in the United States, including an updated version published in 2006.  

Subsequent books include Hope, Human and Wild , about Curitiba, Brazil and Kerala, India, which he cites as examples of people living more lightly on the earth; The Comforting Whirlwind: God, Job, and the Scale of Creation, which is about the Book of Job and the environment; Maybe One , about human population; Long Distance: A Year of Living Strenuously , about a year spent training for endurance events at an elite level; Enough , about what he sees as the existential dangers of genetic engineering; Wandering Home , about a long solo hiking trip from his current home in the mountains east of Lake Champlain in Ripton, Vermont back to his longtime neighborhood of the Adirondacks. His most recent book, Deep Economy: the Wealth of Communities and the Durable Future , was published in March 2007. It addresses what the author sees as shortcomings of the growth economy and envisions a transition to more local-scale enterprise.

In late summer 2006, Bill helped lead a five-day walk across Vermont to demand action on global warming that some newspaper accounts called the largest demonstration to date in America about climate change. Beginning in January 2007 he founded stepitup07.org to demand that Congress enact curbs on carbon emissions that would cut global warming pollution 80 percent by 2050. With the help of six college students, he organized 1,400 global warming demonstrations across all 50 states of America and gained the support of environmental, student and religious groups. Step It Up 2007 has been described as the largest day of protest about climate change in the nation's history. A guide to help people initiate environmental activism in their community, coming out of the Step It Up 2007 experience and entitled Fight Global Warming Now, will be published in October 2007.

Bill is a frequent contributor to various magazines including The New York Times, The Atlantic Monthly, Harper's, Orion Magazine, Mother Jones, The New York Review of Books, Granta, Rolling Stone, and Outside. He is also a board member and contributor to Grist Magazine.

Bill has been awarded Guggenheim and Lyndhurst Fellowships, and won the Lannan Prize for nonfiction writing in 2000. He has honorary degrees from Green Mountain College, Unity College, Lebanon Valley College and Sterling College.

Bill currently resides with his wife, writer Sue Halpern, and his daughter, Sophie, who was born in 1993, in Ripton, Vermont. He is a scholar in residence at Middlebury College.