The Pacala-Socolow paper on stabilization wedges, published in the August 13, 2004, issue of Science, presents an extremely simple model. Understanding why the paper has been so positively received in many quarters can help guide the research strategy directed toward integration of CMI efforts for the next five years.

The wedges work produced a way of working around two barriers that have thwarted early action to mitigate climate change. The first barrier has been the lack of convergence in answers to the question: “Is the Mitigation of Climate Change an Urgent Task?” By “urgent,” we mean “requiring planning within this decade of multi-decade campaigns to reduce global carbon emissions.” Environmental scientists overwhelming answer, “yes.” Those who develop “integrated assessments,” which blend economics and environmental science and often work with a time frame of 100 years, often find that their models answer, “no.” Uncertainties in the estimates of the damages from climate change and the costs of mitigation are so large that the recommendations for delay implied by integrated assessments cannot easily be defended, but no alternative prescriptive analyses have been available for policy making.

The wedges work provides an alternative perspective, which assumes that early action is desired and asks: “What does that action look like?” An answer to that question, we assert, is indispensable before any judgment can be made about the merits of early action. The less arduous early action is found to be, the more credible it becomes that early action is warranted.

The second barrier has been a point of view, widely held as recently as two years ago, that no technologies are available to mitigate climate change. Those institutionally opposed to early action have claimed that the only appropriate response to the challenge of climate change is an increased research effort to develop entirely new mitigation options. Supporters of this point of view cite refereed papers that observe that the magnitude of necessary mitigation exceeds the capability of any single mitigation strategy, brought to bear on its own. This is an unfortunate misreading of these papers. These papers are entirely consistent with a view of mitigation as a set of parallel campaigns to develop mitigation technologies, each of which does only part of the job.

The wedges paper deals with only the next 50 years, which we assert is the longest credible time interval for concrete thinking about the climate problem by private-sector and public-sector decision-makers. The paper introduces: 1) the “stabilization triangle” to approximate the magnitude of the job of mitigation, and 2) the “stabilization wedge,” as a new physical unit with which to measure the magnitude of individual contributions to mitigation. The wedges analysis could have led to discouragement, inasmuch as every individual wedge is a daunting amount of activity. Instead, it elicited positive thinking and specificity in emergent discussions of early action, by providing strong evidence that climate change mitigation is feasible, even if terribly difficult.

The success of the wedges model creates four lines of further development for the next five years:

  1. We will investigate more deeply the “business as usual” CO2 emissions scenarios that provide the point of reference for determining the magnitude of the task of stabilizing the CO2 concentration of the atmosphere.
  2. For several specific wedge strategies, we will help formulate policies bearing on early deployment and seek to clarify issues of scale-up threatening to impede very widespread deployment.
  3. We will help develop criteria for comparisons across wedge strategies.
  4. We will enlarge the wedge analysis, at a similar level of generality, to take into account other objectives of a transformed energy system, notably issues related to “energy security.”


Scenarios of business-as-usual CO2 emissions

One particularly important issue is the question of “virtual wedges,” that is, CO2 emissions reductions that occur even without climate policy. To what extent can virtual and real wedges be uncoupled (because what happens in response to explicit carbon policy is qualitatively different from what happens without carbon policy)? The deployment of technologies for CO2 capture and storage from fossil fuels (CCS) and bio-sequestration in soils and forests requires deliberate carbon policy, but the deployment of other wedge technologies may not. To what extent will decarbonization take the form of “more of the same,” an intensification of trends nearly certain to occur anyway?

With visiting economist, Richard Tol, we are exploring business-as-usual scenarios by asking how the energy system evolved in the past. We are reconstructing U.S. carbon emissions since 1850 to estimate the virtual wedges that have already appeared. Over the past 150 years, trends in CO2 emissions have been dominated by changes in the fuel mix: during industrialization, renewables were replaced with coal, but later on, coal lost its dominant position to cleaner oil, natural gas and nuclear power. Over the last 30 years, the growth in the energy-extensive service sector is the main reason that CO2 emissions have grown relatively slowly, at about the same pace as the population.

We will develop simple yet process-based models that are capable of reproducing the last 150 years. In collaboration with Tol and Klaus Keller, we will be using data assimilation methods to calibrate these models. This will provide a sound statistical basis for building probabilistic scenarios of future energy use and carbon dioxide emissions.


Individual wedge strategies: Policies to enable early deployment and issues of scale-up

The wedge strategies introduce three broad categories of new technology:

  • Efficiency technologies for buildings, vehicles, and industry.
  • Non-carbon primary energy (renewable and nuclear energy, in several forms) that can significantly supplement the fossil fuel system.
  • Advanced conversion technologies that produce electricity and fuels cleanly from coal, natural gas, and biomass, with CO2 capture and storage (CCS).

The penetration of these technologies into the world’s economies will be accelerated by well crafted regulations, incentives for innovation, subsidies for the poor, and programs of research development, and diffusion. An unprecedented level of creativity in synthesizing policy analysis, technology assessment, and environmental insight will be required. We intend to contribute selectively to this effort.

We will seek collaborators to work on energy efficiency in buildings. The end-use perspective has become less prominent in energy discussions than two decades ago. Rarely is it mentioned in today’s energy discussions that, for example, 70% of U.S. electricity is consumed in buildings and 70% of U.S. petroleum is consumed in vehicles. Buildings are coal field and vehicles are oil fields. We will build on our wedges work to emphasize the larger systems boundary that contains the energy consumer as well as the energy producer.

We will join with Princeton colleagues in the Program in Science and Global Security, collaborators for three decades, in investigating the implications of a possible resurgence of nuclear power for the proliferation of nuclear weapons. We will explore whether an international regime can emerge that is matched to the weapons implications of one or more wedges of civilian nuclear power.

We will continue to put in context the large fraction of past and future CMI effort on precombustion capture of CO2 from solid fuels (coal, petcoke, and biomass) and its geological storage. The size of the CCS opportunity (Is one wedge available? Two? Three?) will be clarified by work in the Capture Group on low-rank coals and in the Storage Group on leakage.

Our work has called attention to the likelihood that the fraction of primary energy directed to electric power will increase more quickly in a world that is constraining its carbon emissions than in a world that is not. This is because there are fewer attractive ways to decarbonize fuels than power. Accordingly, carbon constraints may elicit the substitution of heat pumps for furnaces and boilers in buildings and plug-in hybrids for self-contained hybrids in vehicles – in both cases, tied to decarbonized power. We will investigate whether this is a trend that can become significant.

A continuing theme of our work is the identification of ways to circumvent potential constraints on large-scale deployment of wedge technologies arising from environmental and social impacts that grow more severe at large scale. The land constraints of biofuels, the intermittency of renewables, the below-ground capacity for CO2 storage, and the availability of natural gas are all examples of such potential constraints.

All of these single-wedge issues must be considered in specific geographical contexts. After the U.S., our greatest interest is in understanding wedge strategies for China and India, with attention to the potential for ‘leapfrogging.” In both countries we will be joining forces with comparably modest projects at Harvard. In China, we are building on a long-term research collaboration with Tsinghua University on clean coal and CCS; we will be extending this effort with the help of students and faculty of Princeton’s Woodrow Wilson School. In India, we are beginning a project on the future of coal, based initially on a single post-doctoral fellow here and colleagues in Bangalore and Bombay with whom we have worked in the past. We will certainly be involved elsewhere in the world as well; we are currently seeking to develop new collaborations on carbon mitigation with researchers based in the Middle East.


Criteria for comparisons across wedge strategies

Over the next several years we will continue to develop criteria to compare and rank wedge strategies. We must first of all respond to the demand from policy makers to develop insights into today’s relative costs. One way to weigh costs at a given time is to ask which choices are impacted first, as a price on CO2 emissions rises. As a rule, choices upstream in the energy system are impacted before choices downstream. This is because overheads (transaction costs) accumulate as energy moves downstream, resulting in the same emissions price becoming a smaller percentage of total cost the further downstream one goes. Thus, a “tax” of $100 per ton of carbon triples the price of coal delivered to a power plant while adding only 25 cents per gallon to the price of gasoline. Hence, wedges of upstream technology are more likely to be elicited by single-price carbon markets than wedges of downstream technology.

Additional criteria emerge when one considers how costs are likely to change over time, especially how costs are likely to change as a result of increasing levels of deployment. Work in collaboration with Klaus Keller will seek to establish the relative importance, across wedge strategies, of two countervailing factors: 1) cost savings from “learning by doing,” and 2) decreasing returns to scale as lowest cost opportunities are deployed.

As emphasized by CMI Advisory Committee member David Hawkins, another criterion can be derived by considering the “future commitments to emissions” inherent in current investments. A new coal power plant, for example, could emit CO2 into the atmosphere for 60 years or more. A new uninsulated apartment building could produce avoidable CO2 emissions associated with heating and cooling for more than a century. This perspective gives priority to wedge strategies that will head off the most durable carbon-oblivious investments. A detailed analysis down this road requires understanding the costs of retrofits at a later time. We intend to explore the potential of an extension of conventional carbon accounting to “double-column” carbon accounting, the usual column for annual carbon emissions supplemented by a second for annual carbon commitments. Our current judgment is that we should help launch such accounting.


Formulations that treat simultaneously carbon mitigation and other objectives

In addition to reducing the risk of dangerous interference with the climate system, five other challenges loom, as the world’s energy system evolves over the next few decades:

  • removing the specter of dangerous confrontations over oil and gas reserves
  • avoiding spiraling costs for energy, and price volatility, which can seriously inhibit economic growth
  • decoupling air pollution and fossil fuel use
  • decoupling nuclear weapons proliferation from nuclear power
  • providing access to modern energy carriers, including clean cooking fuels and electric power, for the poorest rural and urban households

As described throughout this document, our program will engage with all five, but probably most of all with the first. We are determined to develop a deeper understanding of the interaction of global energy security concerns with global climate concerns. To this end, we are building a joint research program with Princeton’s Program on Near East Studies, focusing on petroleum. Areas of attention include resource availability, local decision-making about resource extraction, and the potential of CCS technologies to expand local resources. We are also focusing new research on two areas of interaction of oil and carbon: 1) the challenge of liquids from coal (likely to be elicited by high-priced oil but a step in the wrong direction from the perspective of climate mitigation unless accompanied by CCS), and 2) the increased market pull on CCS from enhanced oil recovery when the price of oil rises.