"Wedge Factor," Feature Article, October 2007

wedge factor

Are there 51 small ways to curb global warming- or maybe just one? A mechanical engineering professor says the best method to curb greenhouse gas emissions is to tackle the problem in a few medium-size chunks.

by Jeffrey Winters, Associate Editor

the compact fluorescent light bulb seems an unlikely symbol: Its glass tubes are fragile and the ballast in its base makes it unwieldy. Even the light it produces is inferior, to some eyes, to that of the century-old incandescent. Nonetheless, the CFL has become the simple and painless answer to what Americans should do about global warming.

If it were all that easy, then there would be no crisis. And though the incandescent light bulb is an inefficient means of producing light, swapping in fluorescents won't come close to saving enough electricity to reduce carbon emissions to the extent that climate scientists and others believe is necessary.

Now that climate change has moved from the pages of Science magazine to those of People, there's a growing call for something to be done—and done as painlessly as possible. Back in April, Time ran a cover article on the 51 things one could do to stop global warming, suggesting such innocuous steps as not making left-hand turns while driving and wearing vintage clothes.

Others see the issue more starkly, as a problem that can be tackled with one dramatic move. In August, for instance, Senator Harry Reid of Nevada called for a moratorium on all new coal-fired power plants worldwide. "There's not a coal-fired plant in America that's clean," Reid was quoted by the Associated Press. "Unless we do something quickly about global warming, we're in trouble." Others also see emissions from coal combustion as the major human contribution to global warming.

Compared to these two approaches, then, Robert Socolow is a downright moderate. Socolow, a professor of mechanical engineering at Princeton University who has studied energy issues for more than 35 years, has written a series of papers outlining a plan of action for reducing the human impact on the climate over the next 50 years. In essence, his idea is replacing Time's 51 small things with seven or so larger ones. But while following the Socolow plan might take some effort and political will, it wouldn't involve shuttering entire industries or requiring citizens to shiver in the dark.

In the three years since Socolow started writing about his proposal, however, neither his plan nor any other has taken effect.

Anticipated Emissions

Projecting present trends into the future is always a tricky business. The models that researchers use to predict changes in the global climate depend upon knowledge of atmospheric science, which has become increasingly sophisticated, and expected carbon emissions from human sources. That latter part is truly unknowable. Wars and plagues might well decimate the global population, and thus reduce its contribution to the atmosphere. Some unforeseen technological breakthrough could render coal, oil, and natural gas obsolete.

The baseline that model researchers use, however, is one in which the global population follows the upward curve predicted by the United Nations, fuel resources remain generally abundant, and economic development and its resultant energy consumption march steadily on. Such a future world is called "business as usual."

Under the business-as-usual scenario, greenhouse gas emissions are expected to double over the next 50 years.

Offsets, Credits & Storage

With its diesel-burning trucks barreling down American highways, J. B. Hunt Transport Services might seem an unlikely pioneer in greenhouse gas reduction. Yet the Lowell, Ark.-based company saw the carbon dioxide emitted from its trucks as an inefficiency that could be cut. In 2003, Hunt began working with Blue Source, a carbon management company based in Holladay, Utah, to evaluate its operations and to find places where greenhouse emissions could be eliminated.

Based on Blue Source's recommendations, Hunt began expanding its intermodal shipping process: For the longest distances, shipments are now sent via rail, while trucks are used for the shorter trips to and from the rail terminal. Compared to long-haul trucking, rail transport was found to reduce greenhouse emissions by a factor of three. In addition, Hunt began rewarding drivers and their managers for reducing the amount of engine idling on their trucks.

There were rewards for the company as well. Because the emission reductions were verified by independent organizations, Hunt was able to sell carbon emission credits to third parties. In fact, the revenues created through the sale of greenhouse gas emission credits were used to fund new emission reduction projects, as well as increase the company's overall efficiency.

Carbon offsets have become a trendy industry. Companies such as TerraPass and Native Energy have specialized in finding environmentally pleasing ways to counterbalance the carbon dioxide emissions of guilty jetsetters. When the Academy Awards or Super Bowl announce that they are "carbon neutral," this merely means they have purchased CO₂ indulgences from one company or another that equal, more or less, the amount of carbon emissions the event is expected to produce.

Such carbon offsets often involve tree planting or changing agricultural practices. Unfortunately, while the bulk of carbon dioxide emitted will stay in the atmosphere for the next century, trees lock up carbon only as long as they are standing and farming techniques can be changed at a moment's notice.

Other companies are taking a more permanent approach to locking up carbon. Blue Source, which grew out of a CO₂ pipeline company, looks at greenhouse gas emissions on an industrial, not personal, scale. Chief executive officer Bill Townsend said that Blue Source, unlike some others in the carbon offset industry, is positioning itself to be a carbon distribution and storage company. "We're not a technology company," Townsend said. "But what we can do is, once the CO₂ is created, we'll find a way to get it disposed of."

One critical piece of an industrial-scale carbon reduction infrastructure is a network of dedicated pipelines to carry CO₂ from point sources, such as power plants, to repositories in depleted gas wells, saline aquifers, or even caverns on the ocean floor. Building that network from scratch would be a daunting task, but fortunately the skeleton is already in place.

"We have today 3,500 miles of CO₂ pipeline for use in enhanced oil recovery," Townsend said. "We'll ride the backs of the oil industry for a while as we build the carbon highway infrastructure." The oil industry's use of CO₂ to make petroleum easier to extract, Townsend believes, will help subsidize some of the carbon sequestration infrastructure.

One Blue Source project in Colorado is a 500-mile-long pipeline that vents into an existing trunk line that transports CO₂ from natural geological formations. When fully operational, it will carry carbon dioxide stripped from natural gas, which today is vented into the atmosphere, and add it to the national network.

When determining where the sequestered carbon is parked, cost is also a deciding factor. Blue Source president Greg Spencer said, "Because the infrastructure is so expensive, you start with the least-cost alternative, which is enhanced oil recovery, which is where you can sell it as a commodity. Then you go to the next tier, which might be aquifers. Then you go to the next tier, which might be ocean sequestration."

Although the Blue Source portfolio is full of energy efficiency projects and switching power plants to low-carbon fuels, sequestration is seen as the biggest potential carbon reduction mechanism. The hope is to have the basic infrastructure in place even before the advent of carbon markets or taxes in the U.S.

"The DOE says that carbon sequestration could be as much as 50 percent of the United States' answer to climate change," Townsend said. "You make a business out of that by not only participating in carbon markets, but using captured CO₂ as a commodity that creates value on its own." —Jeffrey Winters

Based on what researchers now understand about the atmosphere and the terrestrial and oceanic carbon cycles, putting that much additional gas into the air would lead to a concentration of atmospheric carbon dioxide by the middle of the 21st century that is double what there was just two or three centuries ago. And, according to the best atmospheric models, that much carbon in the air would likely lead to pronounced changes in the climate. Continuing business as usual over the next 50 years also would mean investing in so much conventional, carbon-spewing infrastructure—power plants and automobiles, in particular—that it could become even harder than it is today to turn away from fossil fuels. Atmospheric carbon dioxide levels would likely rocket to three or more times the pre-industrial level and, according to climate predictions, the increase could have dire consequences.

Beginning in 2004, Socolow, together with Stephen Pacala, the co-director of Princeton's Carbon Mitigation Initiative, started outlining a strategy to avert this crisis. One of the key differences between Socolow and Pacala's strategy and other proposals lies in its simplicity.

Reports by the Intergovernmental Panel on Climate Change—the U.N. body charged with monitoring global warming—or other groups are replete with alternatives to the business-as-usual scenario and the resultant impact on the atmosphere. Generally, these alternatives are charted with curves of emissions and carbon concentrations soaring and swooping across the graph. Comparing one to another is difficult at best.

Socolow and Pacala clarified the situation by simplifying it. The business-as-usual scenario calls for almost straightline increases in emissions, from 7 billion tons of carbon (or, including the oxygen atoms, 25 billion tons of carbon dioxide) in 2004 to 14 billion tons of carbon in 2054. Conversely, holding carbon emissions flat over the same period and then substantially reducing them would slow the buildup of greenhouse gases in the atmosphere sufficiently to likely avoid disastrous climate changes.

On a chart, the difference between the two paths is a right triangle, 7 billion tons of carbon per year tall and 50 years wide, or 175 billion tons wide total. Socolow and Pacala then took that large triangle and sliced it into seven smaller, more manageable wedges, each 50 years wide and 1 billion tons of carbon per year tall, and began hunting around for schemes for avoiding not the entire triangle, but single wedges. In a demonstration of how the wedge strategy would work, they listed 15 out of the many possible ways to cut 25 billion tons of carbon. To defeat global warming, they said, we need to enact seven of them.

A couple of those wedges involve agricultural and forestry practices. But the vast majority of them go to the heart of the way power will be generated and used in the coming decades. Doubling the fuel economy of the world's automobiles— projected to be about 2 billion by 2054—from a business-as-usual 30 miles per gallon to 60 mpg gives you one wedge. Cutting worldwide domestic and commercial electricity use by 25 percent gets you another wedge. So would tripling the amount of nuclear-generated electricity, or increasing the amount of wind-generated electricity by a factor of 40, as long as either step replaced electricity generated by coal.

The wedge idea, first published in the journal Science, made quite a splash after its publication in 2004. Policy makers and advocates have focused on the 50-year timeframe as one that enables the changes needed to take on global warming to start small and build over time.

Since the 2004 paper, others have pushed proposals for slowing down greenhouse gas emissions. At the end of the movie An Inconvenient Truth, a number of small-bore ideas flashed across the screen. Another visible effort in that vein made the cover of Time in April of this year: 51 Things You Can Do to Make a Difference. Time's list included such items as paying bills online and using a rake instead of a leaf blower when doing yard work.

While it is certainly true that line drying clothes (item No. 7 on the list) would help at the margins, Socolow worries that such advice gives the wrong impression about the challenges ahead. Indeed, it takes a considerable change to account for just one of Socolow's carbon wedges. One such wedge, for example, is cutting the projected number of miles driven in 2054 by half, to 5,000 per car annually. Accomplishing that goal would require changes beyond technology, to include urban planning and no small amount of social engineering.

The other approach, one that has only recently gotten attention, is to simplify the problem beyond what even Socolow and Pacala propose. In this new view, the main issue is coal.

As outlined in an argument written by James Hansen and Pushker Kharecha of the NASA Goddard Institute for Space Studies in New York, conventional natural gas and oil supplies are limited and it's likely that their production will begin to decrease in the coming decade. Although that promises to be a major problem for motorists, many industries, and others who are currently dependent on oil and gas, it also means that, barring some unforeseen development, carbon emissions from those fuels are constrained.

Plugging data from the Energy Information Agency on existing and likely oil, gas, and coal reserves into standard climate models, even the business-as-usual scenario doesn't produce as much carbon emissions as many fear, simply because there's a lot less carbon around to emit. In fact, if there were only one trillion barrels of conventional oil remaining to be used (as many observers believe), then burning through all of that would raise carbon dioxide by just 65 parts per million. The potential carbon contribution from likely natural gas reserves is even smaller.

Carbon Two-Step

By themselves then, oil and gas can't push the climate into the danger zone. "If you only look at conventional oil and gas reserves," Kharecha said, "there don't seem to be enough reserves to push us past what we consider to be the dangerous level of atmospheric CO₂." Nature herself may well be spotting us a couple of bonus wedges. Burning through the coal reserves, however, changes the equation.

15 Wedges

According to a plan worked out at Princeton University, any one of the following strategies can cut greenhouse gas emissions by 25 billion tons over the next 50 years. The developers argue that, if we adopt enough of these wedges, carbon emissions will remain steady, rather than double to 14 billion tons annually in the next half-century.

More Efficient Vehicles
Double the fuel economy of world's car fleet to an average of 60 miles per gallon.

Reduce Vehicle Use
Cut the miles driven by the world's car fleet by half, to 5,000 miles per year.

More Efficient Buildings
Cut emissions from buildings and appliances by 25 percent.

More Efficient Coal Power Increase average plant efficiency to 60 percent.

Burn Gas Instead of Coal Replace 1,400 GW of baseline coal power with gas plants.

Capture CO₂ at Power Plants
Sequester emissions from 800 GW of coal or 1,600 GW of natural gas power plants.

Capture CO₂ at Hydrogen Plants
Sequester carbon emissions from plants producing 250 million to 500 million tons of H₂ a year.

Capture CO₂ at Synfuel Plants
Sequester emissions from plants making 30 million barrels of oil a day from coal.

Replace Coal Power With Nuclear Electricity
Add 700 GW of nuclear generating capacity.

Replace Coal Power With Wind
Add 2 million 1 MW wind turbines.

Replace Coal Power With Solar
Add 2,000 GW of photovoltaic capacity.

Replace Gasoline With Wind-Generated Hydrogen
Add 4 million 1 MW wind turbines to make H₂ through electrolysis.

Replace Petroleum With Biofuel
Add 100 times the present U.S. ethanol production.

Revitalize Tropical Forests Eliminate tropical deforestation and add more than a million square miles of tree plantations.

Mandate Conservation Tillage
Apply conservation tillage techniques to all cropland.

In light of this, Hansen has begun calling for a two-step program. The first is an immediate moratorium on new coal-fired power plants that lack carbon capture and storage facilities, and a gradual phase-out of existing plants unless they are retrofitted to capture emissions. "If we must use coal," Kharecha said, "then it must be used in power plants that have carbon capture and sequestration technology." The second step is a carbon pricing mechanism-either a tax or a cap-and-trade system-that will slow oil and gas use.

"It's important to realize, however, that we have incorporated only conventional reserve estimates into our analysis," Kharecha said. "Once you factor in the unconventional estimates for oil or natural gas, which are believed to be vast, then all bets are off." In addition, liquefying coal into motor fuel, a popular answer to the possibility of limited oil supplies, would have the same effect as burning it in a power plant.

For his part, Socolow said there is not as much disagreement between his wedge proposal and the Hansen coal moratorium. "Quite a few of our wedges involve what you build if you don't build conventional coal plants," Socolow said. "I think it's risky to keep the list quite that short. We need to improve our vehicles. But, if I had to name two, I'd name those two."

The only way for any plan to work is to actually carry it out, and thus far the efforts from both individuals and governments have been about as effective as line drying clothes in a rainstorm. True, carbon emissions in the U.S. went down in 2006, but that's almost entirely attributable to record gasoline prices. For the world as a whole, in the last three years for which we have firm data, carbon emissions have gone up by nearly one billion tons per year.

"We now have to say that it's an eight-wedge problem," Socolow said.

Also, since writing the first paper on wedges, Socolow has seen a growing expectation that coal—not natural gas— will be the fuel of choice for the next generation of power plants. That natural gas has fallen out of favor, due in part to higher prices than expected, makes tackling the climate problem tougher.

On the other hand, there have been some measures of progress. The European Union has had a trial with a carbon-trading market that might be a means to support efficiency and carbon-avoidance programs. There is also, Socolow said, a growing awareness that not only is there a problem, but that there are real strategies available to deal with them.

In the past three years, Socolow said, "There's been an avalanche of attention to this topic. You could say we're psychologically under way."

Enacting seven changes that each reduce emissions by 25 billion tons of carbon would level off greenhouse gas production in the next 50 years.

One of the most important places where this new realization has taken hold is in the engineering community, which Socolow said is much more open to the idea of getting on board with solutions to climate change—through wedges or some other mechanism—since the 2004 paper in Science.

"The field understands that there are tremendous opportunities for people with mechanical engineering backgrounds to get involved with what's going to be a major transition," Socolow said. "There's actually going to be a general shortage of manpower."