The 15 wedges outlined in Science reach into all corners of the energy sector, from the widespread capture and storage of a power plants' carbon dioxide emissions to a dramatic escalation of electricity generated from renewable sources such as wind or solar power. They are land-management choices, such as halting deforestation or expanding the use of no-till agriculture, in which farmers leave corn stalks and other post-harvest plant materials on the ground to decompose into rich organic matter.
What else? City planners could make a wedge if they helped reduce commuting distances. Architects assist with more efficient energy use in homes and office buildings. (Click here to see complete wedges chart.)
Socolow, a mechanical and aerospace engineer who co-directs the Carbon Mitigation Initiative -- a joint project of Princeton University, BP and Ford Motor Co. -- said the original paper he wrote with Pacala, an ecologist, did not outline all the possibilities.
"There were many more wedges," Socolow said. "It was a matter of rhetoric to stop at 15. And exhaustion. There was nothing magic about 15."
The profs hatched their idea after seeing one pessimistic scientific report after another about climate change. The topper came when they heard Spencer Abraham, who was then-secretary of Energy, dismiss the idea of capping greenhouse-gas emissions because there were no ready-to-use technologies that could do the job.
"We said, 'That just isn't right,'" Socolow recalled.
So the two set out to show greenhouse gas emissions could be cut with today's technologies, and some major changes in how they are deployed.
In a speech sponsored by the World Bank last March, Socolow encouraged all in the audience to come to the consensus for the sake of his talk that climate science was settled and the Earth's concentrations of greenhouse gases were on a trajectory that the risk-adverse believe requires action. Next, he insisted the audience to come to the consensus that fossil fuels would remain a vital mix for energy production.
"It is, of course, an uncomfortable box," he said.
Click here to hear Socolow describe the wedges concept (Windows Media Player required).
To fully understand the wedge process, you need to know a little about atmospheric science.
The greenhouse gas concentration in the atmosphere today is about 380 parts per million, a stark contrast with the 280 parts per million at the start of the Industrial Revolution more than 200 years ago.
Scientists warn of irreversible rising temperatures if concentrations go much beyond 450 parts per million, opening the door to higher sea levels and disappearing coastlands. If the world does nothing but continue with business as usual, emissions appear headed for 800 or more parts per million by mid-century.
Socolow and Pacala picked 500 parts per million as their target. The number, they said, was chosen to assuage both environmentalists' demands, industry concerns and scientific findings.
Next come a series of simple, back-of-the-envelope calculations telling them how to make a wedge. With each technology, they find the cumulative benefits if it were used over 50 years.
There is nothing hard and fast about this. The scientists chose the 50-year timeframe -- not 75 or 100 years -- because it was easiest for people to grasp. Think of it, Socolow and Pacala say, as the length of a scientist's career.
To become one of the 15 wedges, a technology must exist today and be in large-scale use. And emission reductions from each technology would have to be measurable.
The wedges include many popular ideas -- and some not so popular. And be aware: What it takes to implement just one wedge can be staggering.
For example, solar and wind are often cited as key ingredients in helping the United States ween itself from imported oil and also because it comes with no emissions. To fill a wedge with solar panels, one would need to amp up the deployment of photovoltaic cells by a factor of 700 -- enough to cover all of New Jersey or 12 greater London metro areas.
Windmills can be worked into a wedge by growing the structures 30-fold from today's growth rates. Can you envision all of Germany with a few windmills in every square mile? That's one wedge.
Betting on the nuclear power wedge? You'd have to triple the world's current capacity of reactor-generated electricity.
Perhaps the wedge with the most potential -- sequestration of carbon dioxide in deep underground rock formations in the United States, Russia, China, Canada and Australia -- must overcome a significant hurdle of its own: proof the emissions stay down.
The idea is to get all sides talking, weighing their options, thinking about the regional benefits of one idea over another, and then making decisions everyone can agree won't be easy.
The wedges, of course, have their shortfalls, criticisms the authors themselves point out at the beginning of their article.
Richard Richels, a senior engineer at the Electric Power Research Institute, welcomes the wedges as means for people to understand there is no silver bullet solution to climate change. But he is concerned it suggests a carefree anodyne that doesn't consider all-important cost factors.
"You've got to get the economics in there," Richels said. "If the train is really going to leave the station on this issue, the price of the ride is going to have to be affordable."
He continued, "We have to find out what it's going to cost to make it affordable. By not including the cost issue, people come away from this thinking it will be a piece of cake. It's going to require some serious bucks. If the environment is priceless, we should be willing to pay some serious bucks to protect it."
One of the Bush administration's top environmental officials said the wedges oversimplify the global warming issue. Jim Connaughton, chairman of the White House Council on Environmental Quality, warned in an interview of the difficulties associated with assessing the benefits of cutting climate change emissions -- at least compared with more traditional sources of pollution like acid rain and smog.
"CO2 is tougher," Connaughton said. "You can't quantify the benefits. You can't quantify the costs. And you can't precisely track the technology pathway like we could for clean air. You don't know what dangerous interference is."
Connaughton said he is skeptical with Socolow and Pacala's chosen target for limiting greenhouse gas concentrations. "Right now, there's no science behind 550 [parts per million]," he said. "It could be 440. It could be 770. It could be 1,000."
People who are most optimistic about the wedges concept say they can help teach lawmakers about the amount of work they face on global warming and teach the public that finding solutions mean more than regulating power plants or automobiles.
Said Vickie Arroyo of the Pew Center for Global Climate Change, whose organization has also outlined a wedge-like strategy: "Our preference is to have more players because it makes it more effective for everybody."
The wedges can help to show which energy technologies and planning decisions could worsen the effects of climate change or require a lot more work to make certain they do no harm. Environmental groups point to coal-to-liquid fuel and new coal-fired power plants that lack carbon-control technologies as potential troublemakers. Also unsavory, they say, are big, new buildings that will stand for decades without efficiency upgrades and communities that sprawl into the hinterlands.
Said Connolly, the former Senate staffer now working for a Washington-based consultant, ML Strategies: "The sooner people are aware of the wedges, the quicker we'll avoid investing in the things that would head us in the wrong direction."
