The Pacala-Socolow Group is pursuing innovative modeling that ties future emissions to national income distributions and the Oppenheimer Group has initiated a historical study of scientific assessments.


Tracking climate responsibility by individual emissions

A new framework for assigning national obligations within a global climate agreement by focusing on individual emissions was completed during 2009 and published in July in the Proceedings of National Academy of Sciences (PNAS). The research develops an innovative proposal for setting national emission targets based on the actual emissions of a country’s individual citizens. It also provides a dynamic process that enables national obligations to be continuously adjusted to reflect relative changes in prosperity. The research combines an income inequality database from the World Bank with CO2 emissions data and projections from the U.S. government’s Energy Information Administration to estimate past and future emissions by individuals in each country or region. The globally averaged per capita annual CO2 emission rate at this time is 4 tCO2/yr; the per capita average is five times higher in the U.S. and three times smaller in India. In Figure 22, the world’s individuals are placed in three bins, arbitrarily choosing partitions at 2 tCO2/yr and 10 tCO2/yr. Most global emissions will come from the so-called “high emitters” (those in the top bin), despite their small share of the global population.

Figure 22. Population (left panel) and emissions (right panel) for three representative individual‐emission categories. The darker parts of the bars show estimates for 2003 and the lighter extensions show additions from 2003 to 2030.
Figure 23. Regional population shares in 2003 and 2030 for the high emitters (>10 tCO2/yr).

The methodology develops geographical distributions of individual emitters that reveal where the high emitters live now and will live in the future. As shown in Figure 23, the high emitters in the OECD and non-OECD countries are projected to contribute approximately equally to global emissions in 2030, in contrast to 2003 when emissions of the high emitters in the OECD were 70% of total high-emitter emissions. China’s share of the high emitters grows dramatically, a reflection of its assumed high rate of economic growth. Total global emissions in 2030 are projected to be two-thirds higher in 2030 than they were in 2003.

The specific proposal explored in this research study addresses international equity in emissions reductions by basing national responsibility on the emissions of only the world’s high emitters, and for accounting purposes treating all emitters at every level the same no matter where they live. For example, if the global goal were to cap global emissions at today’s level in 2030, roughly 1 billion people living in 2030 would have emissions high enough to be included in the allocation accounting. This group of individuals would be roughly equally distributed in the US, other OECD, China and other non OECD countries – each with one quarter of a billion high-emitters.

Fresh, and even surprising, insights emerge when the focus moves from high-emitting nations to high-emitting individuals. A focus on individual emissions that goes beyond nationally averaged per capita data and reveals all of the world’s high emitters provides an important tool for dealing with the decarbonization transition that lies ahead.

Of the six PNAS co-authors, four were based in CMI. The effort was led by Shoibal Chakravarty and Massimo Tavoni, CMI post-docs who continue to develop these ideas. They were joined by CMI co- PIs Steve Pacala and Robert Socolow, as well as Ananth Chikkatur (until recently at the Kennedy School at Harvard) and Heleen deConinck (ECN, the Netherlands). The key idea of basing national obligations on the emissions of the nations’ high emitters was cited as one of The 50 Best Inventions of 2009 (and placed at #12) by Time magazine in its Dec. 8, 2009, issue.

In related work, Jie Li, a Ph.D. student in the Science, Technology, and Environmental Policy (STEP) program at the Woodrow Wilson School, applied this concept to the provinces in China. She asked: If China were to adopt a national CO2 target for a future date and were to use the individual-emissions methodology to allocate obligations among its provinces, what would be the outcome? She found an important generalizable result: when emissions associated with energy production are allocated to the sites of production (coal mines, gas and oil fields), people living in the regions containing these sites have inflated emissions – unrelated to their own energy use. A better allocation scheme in the spirit of the currently proposed accounting scheme based on high emitters would assign emissions related to energy production to the sites of consumption of these fuels. Incorporating trade is not straightforward, however, because of the multiple stages between fossil fuel extraction and consumption of final goods and services. Jie will defend her thesis in April 2010. She is currently a Young Professional at the World Bank.


Forecasting air travel demand

Shoibal Chakravarty and Massimo Tavoni are analyzing global and regional air travel demand with an innovative model that uses individual income distributions at the national level. Their empirical investigation seeks to identify the main drivers of the demand for air travel, a sector characterized by a steady and rapid growth in the past 20 years. Indeed, air travel demand is growing roughly 50% faster than overall economic activity. Their research bears on climate change, inasmuch as the currently small contribution of aviation to global CO2 emissions (about 5%) is on track to become much larger, creating concerns regarding the industry’s sustainability. The small number of “clean” alternatives amplifies these concerns. Another important reason for studying air travel demand is that flying dominates the carbon footprints of many high-emitting individuals – and the emissions of high-emitters are at the core of a new scheme for allocating global emissions reduction across nations in another CMI study (see above).

The existing literature identifies income as the most relevant driver of demand, yet this relationship seems not to have been characterized explicitly. The authors’ analysis seeks to fill this gap by starting from income distribution data within countries and a global panel data set of country-level air travel. They find evidence of a sigmoid relationship between income and flying, marked by a steep take off in air travel demand beyond individual incomes of $20,000 to $30,000 that compares well with data from US surveys of travel demand, and the beginnings of a plateau only at much higher values. Combining this sigmoid relationship with assumptions about income growth and income distribution enables air travel demand projections at the national level. Flying will keep growing in most developed countries. As for the developing countries, those projected to experience strong economic growth will not see saturation of demand until far in the future. Nation-level projections of growth in aviation out to 2050, for specific assumptions about rate of growth and distribution of income, suggest that carbon dioxide emissions from air travel could increase three to five times for some countries, and as much as eight times for China. Global demand, shown in Figure 24, exceeds ten trillion revenue-passenger-kilometers between 2030 and 2040.

Figure 24. Projected global demand for air travel, in Revenue Passenger Kilometers. The green, blue and red bands show model projections for different levels of demand saturation, assuming 0%, 0.5%, and 1% growth per year in the duration or distance of the average flight. The red and green dots are projections from Airbus and Boeing, and the curves are projections from the World Business Council for Sustainable Development.


Can China achieve tough environmental goals?

This is the question that has motivated the Ph.D. thesis of Yuan Xu, also a Ph.D. student in the Science, Technology, and Environmental Policy (STEP) program at the Woodrow Wilson School, and a member of the Pacala-Socolow Group. In 2009, Yuan did field work at eight coal power plants in several provinces in China to learn first-hand about the national campaign to install sulfur dioxide scrubbers. These visits confirmed his initial finding that incentives within the program were achieving their objective of getting scrubbers not only built and installed, but also put into operation.

Yuan’s thesis documents the extraordinary rate of installation of scrubbers at coal power plants beginning in 2006. Over the three years, 2006 through 2008, China deployed 324 GWe of SO2 scrubbers, each year the equivalent to the entire U.S. scrubber fleet that was accumulated over three decades. In 2008, China spent over $6 billion in the construction and the operation and maintenance of SO2 scrubbers. Economic-incentive environmental policies for the first time played a major role and were effective in assuring that most SO2 scrubbers operated normally. As a result, average SO2 emissions per kWh of coal electricity in 2008 were down by about a half from their 2005 level.

Yuan’s thesis traces this achievement to new environmental goals set by China’s leaders in its 11th Five Year Plan (2006-2010). Despite China’s colossal failure in the 10th Five-Year Plan to reduce its sulfur dioxide emissions, and in the face of rapidly increasing coal consumption, China in the 11th Five-Year Plan established the goal of 10% reduction of national SO2 emissions by the end of the period, relative to the beginning. The entire Chinese government was mobilized – not only at the central level but more importantly at local levels – to work effectively for the attainment of this goal. The non-cooperation of local governments was effectively discouraged, and local leaders were promoted and removed based on relevant performance. Intensive capacity building was pursued in environmental inspection, monitoring, and statistical data compilation. China in the first three years (2006-2008) reduced its SO2 emissions by 9%.

Yuan conjectures that the 11th Five-Year Plan may mark a historical shift in China’s approach to environmental protection. China’s newly gained confidence in achieving tough environmental and energy goals, together with the mounting international pressure and domestic concern regarding climate change, are probably significant factors behind China’s first-ever goal-setting for CO2 emissions, expressed in terms of reductions in the carbon intensity of the economy, that China’s leadership articulated in the run-up to the Copenhagen meeting in December 2009. Yuan will defend his thesis in February 2010 and begin post-doctoral work at MIT.


Nuclear power and climate change

Robert Socolow and Alex Glaser published a paper in the Fall 2009 issue of Daedalus, the journal of the American Academy of Arts and Sciences, entitled “Balancing risks: Nuclear energy and climate change.” Five arguments capture the essentials of their paper:

Nuclear power could make a significant contribution to climate change mitigation. To do so, however, nuclear power must be deployed extensively in many developing countries that increasingly share production and consumption patterns with the industrialized world. Some of these countries are politically unstable today. If nuclear power is sufficiently unattractive in such a deployment scenario, nuclear power is not on the list of solutions to climate change.

Nuclear power will not benefit climate change if its contribution is withdrawn a decade or two after global scale-up begins, as a result of the coupling of nuclear power to nuclear weapons. The coupling of nuclear power to nuclear weapons is the most critical flaw of nuclear power today and is the result of nuclear power’s inadequate system of international governance and its reliance on uranium enrichment plants and reprocessing plants under national control.

A world considerably safer for nuclear power could emerge as a co-benefit of the nuclear disarmament process. A multilateral nuclear disarmament process might be the most effective way– perhaps the only way–for states to decouple nuclear power from nuclear weapons.

The next decade is critical. It can used to establish international ownership of uranium enrichment, the cessation of all spent fuel reprocessing, and much more effective norms of international governance.

Every “solution” to climate change can be done badly or well. Done badly, solutions can be worse than the disease. Making climate change the world’s exclusive priority is therefore dangerous.

Conceding that such conclusions can embody only the most subjective of considerations, the authors judge the hazard of aggressively pursuing a global expansion of nuclear power today to be worse than the hazard of slowing the attack on climate change by whatever increment such caution entails. If over the next decade the world demonstrates that it can do nuclear power well, a global expansion of nuclear power would have to be – indeed, should be – seriously reexamined.

This work has received attention through the setting of the Doomsday Clock by the Bulletin of the Atomic Scientists. Both Glaser and Socolow, as members of the Science and Security Board of the Bulletin, participated in the decision to set the clock back by one minute (a judgment that in the past year global safety has increased), and the paper was cited explicitly in the background paper that announced this decision.


Lessons from recent scientific assessments

Michael Oppenheimer and colleagues are carrying out research on past environmental science and scientific assessments. The role of scientific assessments in the evaluation of knowledge has expanded over the past three or four decades to become an integral factor in shaping government policy on climate change. But how well have these scientific assessments worked, and how might they be made to work more efficiently and effectively in the future?

The ozone case, particularly the creation of the Montreal Protocol, is widely regarded as an example of successful policy-making (which came about, some analysts have argued, as a result of widespread scientific consensus). At the same time, it is also an example of at least two scenarios that scientists and policy makers would wish to avoid if possible: an unexpected outcome of great import (the Antarctic ozone hole), and the tendency to follow a path of learning that turns out to have decreasing, rather than increasing correspondence with the correct answer over time (negative learning). In the case of ozone depletion, scientists initially dismissed from consideration knowledge that turned out to be critical – heterogeneous chemical reactions occurring on the surfaces of polar stratospheric cloud particles and volcanic aerosols.

At the time, gas phase atmospheric chemistry was much better understood than multi-phase chemistry, and heterogeneous reactions were seen as arcane and generally unimportant to atmospheric processes. Because scientific knowledge of heterogeneous chemistry was both uncertain and thought to be unimportant, the earliest ozone assessments either ignored heterogeneous reactions entirely, or mentioned them only to dismiss their possible significance. Scientists did not address heterogeneous reactions in detail, as potential contributors to ozone depletion, until they were forced to by the discovery of an unexpected phenomenon: the Antarctic ozone hole, which made them realize that their models were either inaccurate or incomplete.

Because heterogeneous reactions are extremely hard to measure, even once it became clear that they were important scientists remained unable to fully incorporate them into their models. They were thus unable to replicate the ozone hole (or mid-latitude ozone depletion, either), and this remains a challenge to this day. Meanwhile, however, policy-makers have been making judgments about ozone depletion despite the absence of accurate models.

There are some intriguing parallels between the ozone case and what is going on now in the assessments of the Intergovernmental Panel on Climate Change (IPCC). The potential for sudden collapse of the West Antarctic ice sheet (WAIS) is as difficult to model and predict in its own way as heterogeneous reactions are in ozone depletion. In the WAIS case, however, scientists have recognized early on that this little-understood phenomenon might prove to have extremely important effects. The researchers’ key focus will be finding lessons in the experience of ozone scientists, assessors, and policy-makers that might benefit the groups currently struggling with the uncertainty caused by WAIS.