Professor Robert Socolow has been immersed in environmental research since the late 1960s, when he dropped his work in high-energy physics to write a textbook about how human activities were changing ecology. Socolow’s primary interest was energy, but in 2000, he began working closely with climate scientists and environmental economists in a Princeton collaboration aimed at addressing the increasing levels of carbon dioxide in the atmosphere.

As Socolow spoke with his new colleagues and read papers in their fields, he noticed a significant gap. For the scientists, escalating levels of greenhouse gases generated by burning fossil fuels posed both short- and long-term threats, warranting immediate action. But economic projections for mitigating carbon dioxide tended to use a 100-year time span, with most of the heavy lifting coming in the latter half of the 21st century and little attention paid to the political will needed to begin widespread cuts in greenhouse gas emissions.

“Where have we made the decision to [postpone cutting emissions]?” Socolow wondered. “Has the society understood what it’s letting itself in for? The messages were not consistent. There were economists who were relaxed and scientists who were nervous.”

Socolow and colleague Stephen Pacala, an ecology and evolutionary biology professor, set out to close the gap by showing how existing carbon mitigation strategies could put the world on the right track in this half century. With a goal of keeping atmospheric carbon dioxide below 500 parts per million — about twice preindustrial levels — they found that worldwide carbon emissions would need to remain at their current level, about 7 billion metric tons per year, for the next 50 years. The burning of fossil fuels is expected to double in that period, to meet demand for energy, so keeping emissions flat seemed like a monumental challenge.

Monumental — but achievable, according to Pacala and Socolow. They presented the problem graphically with a “stabilization triangle,” where the base represents flat emissions, the ramp shows increasing demand, and the right side marks the end of the 50-year time frame (see p. 20). No single technology can cut emissions while meeting expected energy demand, so the authors split their triangle into pieces, or wedges. Each wedge is a significant, long-term undertaking — doubling the fuel economy for 2 billion cars, cutting building and appliance emissions by a quarter, or doubling the current capacity for generating nuclear energy, for example. Stabilization, they found, requires seven wedges. They presented 15 options.

In August 2004, Science published their paper, and attention soon followed. Al Gore included the wedges concept in his 2006 film, An Inconvenient Truth, and New York Timescolumnist Tom Friedman has used Pacala and Socolow’s work to illustrate the scope of the transformation needed to address climate change. Earlier this year, Time included the Princeton professors in its list of the world’s 100 most influential people. Among researchers, the paper’s terms have become part of the language of climate change. “People say, ‘What part of a wedge would that technology be?’ ” says Tom Kreutz *88, a chemistry Ph.D. who studies power plants for the Princeton Environmental Institute, “and everybody knows what that means.”

Pacala says the wedges paper has “the least intellectual content” of any he’s written, but it also may be the most enduring. Each year, the authors receive dozens of invitations to speak about the wedges concept for audiences that have included congressmen, CEOs, and most recently, the U.N. General Assembly, which Socolow addressed in July.

“It seems as if the more you are at the top of an organization — political leader, the head of a company — the more you like this, because it gives you a sense of the size of the problem,” Socolow says. “You feel empowered.”

The two authors have become the public faces of Princeton’s contribution to curbing climate change. Pacala is reaching the prime of his career, having recently been elected to the National Academy of Sciences, and Socolow, one of Princeton’s first hires in environmental and energy research, maintains an influential voice in the field at age 70. But there are many more faculty members taking an active role in both the science and policy of climate change.

Pacala and Socolow’s ‘wedges’: To keep atmospheric carbon dioxide below 500 parts per million in the next 50 years, worldwide emissions will have to remain at current levels – about 7 billion metric tons per year. But with growing energy demand, the world seems headed toward doubling its annual emissions. The space between those divergent paths is the stabilization triangle. Pacala and Socolow have divided the triangle into seven wedges, each of which could grow to reduce carbon emissions by at least 1 billion tons per year by 2055. Wedge strategies include increasing transport efficiency, capturing and storing carbon from power plants, using more biofuels, and a dozen other options.

Michael Oppenheimer, the Albert G. Milbank Professor of Geosciences and International Affairs, was a lead author for the most recent assessment by the United Nations’ Intergovernmental Panel on Climate Change (IPCC). Robert Williams, a senior research scientist, studies sustainable energy, from wind to switchgrass, continuing work that dates back to the 1970s. Professor Jorge Sarmiento has unparalleled expertise on the ocean’s carbon cycle, and several other professors and graduate students are doing leading-edge work in their fields.

Among the world’s top institutions, Pacala says, Princeton is in a unique position to address climate change, because in addition to faculty strengths in geosciences, engineering, and public and international affairs, the University has collaborations with two major federal research laboratories located just across Route 1. The Geophysical Fluid Dynamics Laboratory (GFDL), run by the National Oceanic and Atmospheric Administration, came to the Forrestal Campus in the late 1960s and now houses some of the world’s premier atmospheric computer modeling. Nearby, the Princeton Plasma Physics Laboratory (PPPL), a Department of Energy facility that grew out of Professor Lyman Spitzer *38’s work in the 1950s, explores fusion, the joining of atoms to produce nuclear power, which Socolow and others in the field see as one of the more promising long-term replacements for fossil fuels. Both labs have close links to Princeton through research, teaching appointments, and graduate programs. “They represent two major units of the world’s science in this field,” Socolow says. “You almost can say everything else fits in between.”

Socolow and Pacala serve as co-directors of the major on-campus source of innovation in carbon research — the Carbon Mitigation Initiative (CMI), a 10-year, $20-million collaboration funded by BP and Ford. When CMI was announced in 2000, it was among the first large consortia to link a university and an energy company. Since then, partnerships between energy and the academy have multiplied and expanded, with some now worth hundreds of millions of dollars. CMI may seem small by comparison, but its impact has been significant.

By providing long-term funding, CMI has enabled some of Princeton’s top minds to explore new projects related to energy on a part-time basis. For example, engineering professors Michael Celia, George Scherer, and Jean Prévost have combined expertise in fluids, materials, and geochemistry to study the potential risks of storing carbon dioxide deep in exhausted oil or natural gas wells. Six years ago, all three were experts in their own fields but novices in carbon storage. Now, says Socolow, “They’ve made a global impact.”

Pacala hopes that the University can duplicate the successes of CMI with its own seed-grant program, Grand Challenges, which was initiated this fall. Professors can apply for up to $100,000 per year for research in three areas: energy and climate; global health and infectious disease; and poverty, land use, biodiversity, and water in Africa. Graduate students and undergraduates will be involved as well, through courses and summer internships.

Addressing global warming relies heavily on engineering, and Princeton’s engineering school seems primed to increase its attention to the problem. Celia, who chairs the civil and environmental engineering department, notes that two new professors focus on environmental research, and more additions could be coming. Elsewhere in the E-Quad, research proceeds on related topics, such as fuel cells, environmental sensors, and combustion.

Princeton’s most immediate impact likely will come in the area of carbon capture and storage. Using specially equipped power plants, energy companies can produce electricity by burning fossil fuels, capture carbon dioxide emissions at their source, and inject the carbon dioxide deep into the oceans or in geological formations, such as oil and gas fields. Celia and his collaborators have focused on the latter storage option.

Oil and gas fields are great candidates, Celia says, because they lie beneath thick caprock formations. The caprock was strong enough to hold oil underground for millennia, so it likely would do the same for carbon dioxide. But oil wells punch pencil-like holes in the caprock, which eventually are filled with cement plugs and steel casings. Injected carbon dioxide can mix with briny water in the ground to form a weak acid — comparable to vinegar or Coca-Cola — that is strong enough to corrode cement. The acidic brine could be a significant problem, depending on how long it stays in contact with a given plug. And even if the plugs remain unharmed, other risks remain, like gaps or cracks created by too much pressure from carbon dioxide injection.

“This is a wonderfully complex problem,” says Scherer, a materials expert who calls himself the “cement guy” of Princeton’s carbon storage team. Researchers still have plenty of questions to keep them busy, but they are moving closer to large-scale models and risk assessments.

BP, spurred in part by CMI research, has announced plans to build two zero-emission power plants using carbon capture and storage at a cost of approximately $1 billion per project, and Celia is hopeful that more will follow. “It is important to produce carbon-free electricity, and we should begin to do so now,” he says. “We can include interesting large-scale experiments with these early storage projects, to answer some of our remaining questions, but we need to get on with solving the atmospheric carbon problem. If we wait another two decades, that’s too long.”

As engineers pursue ways to solve the carbon problem, several Princeton professors continue to study just how large the problem will be. Earlier this year, the IPCC, the U.N.’s panel of climate experts, noted several key points of scientific agreement — the burning of fossil fuels has increased greenhouse gas concentrations in the atmosphere, evidence of warming is “unequivocal,” and more severe changes are “very likely” — but many details still require exploration. For instance, scientists know that not all of the carbon dioxide that humans put into the air stays there. But how much is absorbed by the oceans and how much enters the terrestrial biosphere? What are the precise mechanisms involved? And what impact will this absorption have on plants and animals?

Historical data may give scientists insight into some questions. For about 20 years, geosciences professor Michael Bender has tried to extract slices of history preserved deep in the ice sheets of Antarctica. Bender and colleagues developed a method for dating gases trapped in ice cores, and their work has helped researchers to chart carbon dioxide fluctuations over hundreds of thousands of years. Now, the goal is to push the record back even farther. Older packets of ice also may have been preserved, sealing snapshots of the atmosphere millions of years ago.

In the contemporary world, researchers are paying close attention to “terrestrial sinks,” or land-based carbon-uptake mechanisms. Plants should reduce some of the potential for global warming, Pacala says, because they “eat greenhouse gases for a living.” With more carbon dioxide in the atmosphere, plants can eat more and grow more. This is true, to some extent, but there are limits. Plants also need other nutrients, like nitrogen and phosphorus, to grow, and the abundance of these nutrients does not keep pace as carbon dioxide increases. To understand how much carbon plants take in, Pacala and colleagues are working on a series of sophisticated measurements, most recently in the northern part of the U.S. Midwest.

Meanwhile, Sarmiento, the director of Princeton’s atmospheric and oceanic sciences program, examines the effects that global warming could have on oceans. Computer models have provided a good understanding of how much man-made carbon dioxide enters the oceans, but researchers are just beginning to understand how global warming might change the ocean chemistry and circulation.

Modeling could answer some of those questions, but laboratory and field experiments also will play a role. Bess Ward, chairwoman of the geosciences department, studies microorganisms and the nitrogen cycle in aquatic environments, with projects that take her from Antarctica to the Chesapeake Bay, and François Morel, the Albert G. Blanke Jr. Professor of Geosciences, researches nutrients in the ocean to better understand how chemistry controls the growth and activity of phytoplankton. The changing chemistry and biology of marine environments, Sarmiento says, could be a “critical problem” for the future.

Faculty members provide instructive examples of bridging the science and policy worlds. Oppenheimer, Socolow, and Pacala may be the most likely to be quoted in print or share their expertise on TV, but other professors contribute their voices as well. Not far from Guyot Hall, Denise Mauzerall, an associate professor of public and international affairs, studies the potential “co-benefits” of reducing air pollution and greenhouse gases. Mauzerall earned a Ph.D. in atmospheric chemistry and also worked in Washington, D.C., for environmental consulting firms and the Environmental Protection Agency. GFDL scientists Isaac Held and Venkatachalam Ramaswamy, who teach graduate-level courses in atmospheric sciences, played key roles in drafting the latest IPCC report, and civil and environmental engineering professor Eric Wood was front and center at a press conference in Trenton last July, presenting findings from “Confronting Climate Change in the U.S. Northeast,” a Union of Concerned Scientists report he co-authored.

A few years ago, a Discover magazine writer invited Sarmiento and two other scientists on a rafting trip to Alaska to discuss the impact of global warming. It was an atypical request, but the soft-spoken oceanographer accepted. Floating down the Upper Ivishak River, Sarmiento asked the reporter why he’d brought them to Alaska. The reporter turned the question back to the scientists, but it was the rafting guide, Sarmiento says, who gave the most eloquent answer: In the future, with global warming, places like the Alaskan wilderness may not exist.

“One doesn’t want to be a pessimist all the time,” Sarmiento says. “My nature is basically an optimistic one, and I keep thinking, well, we’ll finally get behind this and we’ll find a way to solve it. I hope we do. Because with some of the consequences that could occur, I just don’t want to leave that legacy to my children and grandchildren. We potentially are a generation that can actually turn a corner on this, if we act now.”

Toward a greener campus

Last summer at Forbes College, Ruthie Schwab ’09 and two assistants set out to turn about 100 square yards of hard-packed dirt into a thriving organic garden. The plot, located a chip shot away from Springdale Golf Club’s 15th green, once served as a pathway for Reunions golf carts. By July, it was producing tomatoes, chard, onions, leeks, and fistfuls of herbs.

Much of the produce went to University dining services, but Schwab knew from the beginning that her garden could not supply the quantities that Princeton’s kitchens require. Instead, she envisioned it as a way for students to get in touch with the food they eat and give more thought to supporting organic farms or buying local produce. In terms of reducing greenhouse gases, the garden is negligible, Schwab says. “But what we contribute is the education to students and the direct contact,” she adds. “We can teach them the importance of their actions and how they can affect change.”

Across Alexander Street, a few hundred yards from the garden, Director of Engineering Tom Nyquist keeps an eye on the larger picture of Princeton’s energy use and carbon emissions, examining desk-sized blueprints of everything from the latest construction projects to the network of campus steam tunnels. He also oversees the small, unseen or barely seen projects that pare down energy use: recalibrating heating and cooling controls, repairing steam traps, and installing low-flow shower fixtures. In the last three years, these small fixes have reduced the amount of steam and chilled water used to heat and cool campus buildings. “A lot of the energy conservation comes from the little things that people don’t see and that are even hard to explain or sound trivial,” Nyquist says. “But when added up over thousands of components it makes a big difference.”

Building maintenance and student gardens might seem disparate, but they both reside under a common umbrella: sustainability. On college campuses, the word covers everything from reducing an institution’s carbon footprint to educating students about environmental issues. Princeton opened its Office of Sustainability in December 2006, and Shana Weber, the inaugural director, has spent much of her time since then working with administrators, faculty, and students to draft a wide-ranging campus sustainability report, slated to reach President Tilghman’s desk later this fall. The report, Weber says, will look at where Princeton stands in areas like energy and transportation, recommend targets for the future, and propose standards for measuring progress.

Each year, the University emits about 150,000 metric tons of carbon dioxide, the large majority of which comes from electricity, heating, and cooling for campus buildings. By using efficient technology, including a cogeneration plant that burns natural gas or diesel fuel to generate both electricity and steam, Princeton has managed to keep its consumption relatively low, but as the campus grows, so does energy demand. Weber says that Princeton is working to “create a physical environment that reflects the educational mission” of the institution, with guidelines that mandate each new campus building to be 30 percent more energy-efficient than code requires it to be.

The University is exploring adding solar panels on south-facing roofs, and a portion of the new Butler dormitories will feature Princeton’s first green roof, with soil and vegetation that capture storm water and provide insulation. Geothermal heating and cooling also could become a larger part of Princeton’s portfolio. The University already takes advantage of underground temperatures to heat and cool graduate student housing at the Lawrence Apartments on Alexander Street, using about 100 geothermal wells, each more than 400 feet deep, and a closed system of circulating fluids. When the system came on line a few years ago, its energy-efficiency was so remarkable that University accountants called the utility company to make sure they were reading the correct meters. The Hibben and Magie apartments could be next in line for geothermal heating and cooling. “We have the resources to test things at the cutting edge,” Weber says, “but we also want to be a model for things that can be repeated elsewhere in places that don’t have the resources we have. Geothermal is potentially one of those.”

While greener buildings are high on Weber’s list of sustainability priorities, she also hopes to improve less measurable things like student involvement and whether Princetonians are being good “environmental citizens.” Before and since Weber’s arrival, a handful of student groups have contributed their voices to the conversations about greenhouse gas emissions and other issues, including Greening Princeton, SURGE (Students United for a Responsible Global Environment), and Princeton Water Watch.

Katy Andersen ’08, a former president of Greening Princeton, says that the mind-set of the University’s student environmentalists tends to be more “analyst” than “activist.” For instance, one of Greening Princeton’s major recent contributions was to lobby for a new course, “Toward an Ethical Greenhouse Gas Emissions Trajectory for Princeton University,” taught last fall by Tom Kreutz *88 of the Princeton Environmental Institute. After gathering data for a semester, students in the class proposed programs that could save money and reduce Princeton’s carbon output by 15 to 20 percent. They also recommended using the savings to fund additional programs that would enable a “revenue-neutral” reduction of close to 30 percent of carbon emissions.

Alternative energy sources and energy efficiency can only go so far in the short term, according to James Kuczmarski ’08, who studied sustainability efforts at several universities for a policy-driven spring seminar on energy use at Princeton, taught by Denise Mauzerall at the Woodrow Wilson School. Students from that course recommended that President Tilghman sign the Presidents Climate Commitment, a pledge to plan for “climate neutrality” that has been adopted by more than 340 college and university presidents, including Amy Gutmann of the University of Pennsylvania and David Skorton of Cornell University.

The Presidents Climate Commitment requires participating universities to meet several short-term targets and to create a timetable for becoming carbon neutral, a goal that generally requires purchasing carbon offsets or credits for funding off-campus projects to reduce greenhouse gas emissions. Princeton, which has not yet joined, would have to buy about $350,000 worth of offsets to be carbon neutral this year.

While supporters of offsets view them as a self-imposed tax that can motivate an institution to reduce its emissions, opponents worry that buying offsets would be construed as shirking responsibility by simply writing a check. So far, the University has not been keen on buying offsets, but Weber says the sustainability committee will examine the idea, and related ethical issues, as it prepares its fall report. An institution’s approach to carbon emissions tends to be the most scrutinized and politically sensitive part of sustainability, according to Weber. “That policy sort of defines your leadership stance,” she says, “so we’re really thinking carefully about how to reflect our intentions in the most transparent way.”