THE SO2 ALLOWANCE TRADING SYSTEM: 

THE IRONIC HISTORY OF A GRAND POLICY EXPERIMENT

Richard Schmalensee 

and

Robert N. Stavins

Prepared for 

The Journal of Economic Perspectives 

August 3, 2012 

 
1

The SO2 Allowance Trading System: 

The Ironic History of a Grand Policy Experiment 

Richard Schmalensee and Robert N. Stavins 

ABSTRACT 

Two decades have passed since the Clean Air Act Amendments of 1990 launched a grand 

experiment in market-based environmental policy: the SO2 cap-and-trade system. That system performed 

well but created four striking ironies. First, by creating this system to reduce SO2 emissions to curb acid 

rain, the government did the right thing for the wrong reason. Second, a substantial source of this 

system’s cost-effectiveness was an unanticipated consequence of earlier railroad deregulation. Third, it is 

ironic that cap-and-trade has come to be demonized by conservative politicians in recent years, since this 

market-based, cost-effective policy innovation was initially championed and implemented by Republican 

administrations. Fourth, court decisions and subsequent regulatory responses have led to the collapse of 

the SO2 market, demonstrating that what the government gives, the government can take away. 

Key Words: market-based instruments, cap-and-trade, Clean Air Act amendments of 1990, 

sulfur dioxide, acid rain 

JEL Classification Codes: Q540, Q580, Q400, Q480 
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The SO2 Allowance Trading System: 

The Ironic History of a Grand Policy Experiment 

Richard Schmalensee and Robert N. Stavins1

 Two decades have passed since the Clean Air Act Amendments of 1990 (CAAA) were signed 

into law, launching a grand experiment in market-based environmental policy. By the late 1980s, there 

was growing concern in the United States and other countries that acid precipitation – the result of sulfur 

dioxide (SO2) and, to a lesser extent, nitrogen oxides (NOx) reacting in the atmosphere to form sulfuric 

and nitric acids – was damaging forests and aquatic ecosystems. In the United States, flue gas emissions 

from coal-fired, electric generating plants were the primary source of SO2 emissions and a major source 

of NOx emissions. In response to this and other concerns, the U.S. Congress passed and President George 

H. W. Bush signed into law the CAAA, Title IV of which established the path-breaking SO2 allowance 

trading program. 

 While the concept of cap-and-trade is now broadly familiar, in 1990 this market-based approach 

to regulating the environment was quite novel. Some were hostile to the notion of trading “rights to 

pollute”; others doubted its workability. Up until that time, nearly all pollution regulations took a much 

more prescriptive, “command-and-control” approach, either by setting uniform emission rate limits on 

classes of emitters or by specifying the type of pollution-control equipment to be installed. Such 

requirements are relatively inflexible, imposing the same abatement path upon a range of generally 

heterogeneous facilities and ignoring the fact that the costs of compliance might vary widely across 

individual facilities depending on their age, technology characteristics, operating conditions, and 

characteristics of fuel used. 

 By the close of the twentieth century, the SO2 allowance trading system had come to be seen as 

both innovative and successful. It has become exceptionally influential, leading to a series of policy 

innovations in the United States and abroad to address a range of environmental challenges, including the 

threat of global climate change (Stavins 2003). Most prominent among these innovations has been the 

European Union Emission Trading System, a carbon dioxide (CO2) cap-and-trade system adopted in 2003 

that is by far the world’s largest environmental pricing regime (European Commission 2012). 

 The design and implementation of the landmark SO2 cap-and-trade system have led to four 

striking ironies that are the focus of this essay. First, subsequent research indicates that in enacting an 

ambitious – and successful – policy to reduce SO2 emissions in order to curb acid rain, the government 

essentially did the right thing for the wrong reason. Second, although the program appears to have been 

successful on nearly all dimensions, a substantial source of its cost-effectiveness was an unanticipated 

consequence of the deregulation of railroad rates in the late 1970s and early 1980s. Third, it is ironic that 

cap-and-trade has come to be demonized by conservative politicians in the last few years, since this 

market-based, cost-effective policy innovation was championed and implemented by Republican 

administrations from that of President Ronald Reagan to that of President George W. Bush. Fourth and 

finally, court decisions and subsequent regulatory responses have led to the virtual collapse of the SO2

market, demonstrating that what the government gives, the government can take away. In order to 

explain these four ironies, we first briefly review highlights of the system’s design and performance. 

 

1

 Schmalensee is the Howard W. Johnson Professor of Economics and Management, Emeritus at the Massachusetts 

Institute of Technology, and a Research Associate of the National Bureau of Economic Research. Stavins is the 

Albert Pratt Professor of Business and Government at the Harvard Kennedy School, a University Fellow of 

Resources for the Future, and a Research Associate of the National Bureau of Economic Research. Their e-mail 

addresses are rschmal@mit.edu, and robert_stavins@harvard.edu. 
3

A fifth, long-recognized irony deserves brief mention. Acid rain itself was largely a consequence 

of compliance with national ambient air quality standards set in the 1970s for SO2 and other localized 

pollutants. In order to reduce local ambient concentrations, electric utilities built more than 400 tall 

stacks, many greater than 500 feet in height (Regens and Rycroft 1988), which successfully dispersed the 

stack gases, but did so by injecting them high enough into the atmosphere that they precipitated out tens 

or hundreds of miles downwind as acidified rain, snow, or particles. 

Design 

 The policy’s objective was to reduce total annual U.S. SO2 emissions by 10 million tons relative 

to 1980. (This section draws on Chan et al. 2012; also see Ellerman et al. 2000.) Phase I (1995–1999) 

required significant emissions reductions from the 263 most polluting coal-fired electric generating units, 

almost all located east of the Mississippi River. Phase II, which began in 2000, placed an aggregate 

national emissions cap of 8.95 million tons per year on approximately 3,200 electric generating units — 

nearly the entire fleet of fossil-fueled plants in the continental United States (Ellerman et al. 2000). This 

cap — affecting almost exclusively the power sector — represented a 50 percent reduction from 1980 

levels. 

 The government gave permits to emit, called allowances, denominated in tons of SO2 emissions, 

to power plants covered by the law. If annual emissions at a regulated facility exceeded the allowances 

allocated to that facility, the owner could buy allowances or reduce emissions, whether by installing 

pollution controls, changing the mix of fuels used to operate the facility, or by scaling back operations. If 

emissions at a regulated facility were reduced below its allowance allocation, the facility owner could sell 

the extra allowances or bank them for future use. These opportunities created incentives to find ways to 

reduce emissions at the lowest cost and to take advantage of low-cost abatement options early. 

 While this policy is seen by many observers as one of the most successful applications of 

economic thinking to environmental policy, the policy’s target was not chosen to maximize net economic 

benefits. (This is true of most environmental policies, of course.) No credible estimates of economic 

benefits at alternative target levels were available. Instead, the target was selected largely based on what 

was believed to be the “elbow” of the abatement cost curve. Also, there was a political desire to choose a 

target level of reductions that was big enough to gain the support of the environmental community and to 

be seen as satisfying a campaign pledge of the new President. Thus the choice of the cap was consistent 

with a positive political economy model of policy making whereby a politically acceptable target is 

chosen with an eye toward avoiding regions of steep change in the policy’s impact on social welfare 

(Baumol and Oates 1971). 

 After the target level of emissions, the second most important design feature of the system was its 

allocation of allowances. Government auctioning of allowances would have generated revenue that could 

have been used – in principle – to reduce distortionary taxes, thereby reducing the program’s social cost 

(Goulder 1995). But this efficiency argument was not advanced at the time; affected utilities and their 

customers’ representatives would have strongly opposed auctioning; and the political value of being able 

to allocate free allowances to address distributional concerns was substantial (Joskow and Schmalensee 

1998). Also, because cost-of-service regulation characterized the entire electric utility industry in 1990, it 

was assumed that the value of free allowances would be passed on to consumers and not generate 

windfall profits for providers. Given that a free allocation was utilized, the distribution could be defined 

in such a way as to ensure the greatest political support, without fear that this would jeopardize the 

system’s environmental performance or economic cost. Absent particularly problematic types of 

transaction costs (Stavins 1995; Hahn and Stavins 2011), a cap-and-trade system’s equilibrium allocation 

after trading is independent of the initial allocation (Coase 1960; Montgomery 1972). 
4

Performance 

 Beginning in 1995 and over the subsequent decade, the SO2 allowance-trading program 

performed exceptionally well along all relevant dimensions. (Early assessments of the system’s design 

and performance were provided by Schmalensee et al 1998 and Stavins 1998.) The program was 

environmentally effective, with SO2 emissions from electric power plants decreasing 36 percent – from 

15.9 million to 10.2 million tons – between 1990 and 2004 (U.S. Environmental Protection Agency 

2011b), even though electricity generation from coal-fired power plants increased 25 percent over the 

same period (U.S. Energy Information Administration 2011). The program’s long-term goal of reducing 

annual nationwide utility emissions to 8.95 million tons was achieved in 2007, and by 2010 emissions had 

declined further, to 5.1 million tons. Overall, the program delivered emissions reductions more quickly 

than expected, as utilities took advantage of the possibility of banking allowances. With its $2,000/ton 

statutory fine for any emissions exceeding allowance holdings (and continuous emissions monitoring), 

compliance was nearly 100 percent. 

The costs of achieving these environmental objectives with cap-and-trade were significantly less 

than they would have been with a command-and-control regulatory approach. Cost savings were at least 

15 percent and perhaps as much as 90 percent, compared with counterfactual policies that specified the 

means of regulation in various ways and for various portions of the program’s regulatory period (Carlson 

et al. 2000; Ellerman et al. 2000; Keohane 2003). In addition to static cost effectiveness, there is 

evidence that the program brought down abatement costs over time by providing incentives for innovation 

in equipment and operating procedures that are generally much stronger than those provided by traditional 

command-and-control regulation (Ellerman et al 2000, pp. 235-48; Popp 2003; Bellas and Lange 2011). 

While the program was less costly than a conventional approach, the costs may not have been as 

low as they could have been. Marginal abatement costs varied significantly across facilities, at least in the 

program’s first two years (Carlson et al. 2000). On the other hand, there is evidence that the 

intertemporal allocation of abatement cost (via allowance banking) was at least approximately efficient 

(Ellerman and Montero 2007), and the pattern of voluntary compliance was consistent with cost-effective 

compliance strategies (Montero 1999). 

The following factors may have kept costs above the theoretical minimum, though the influence 

of each has been debated: (1) provisions in the CAAA that encouraged early use of flue-gas 

desulfurization (using devices called “scrubbers”) instead of switching to low-sulfur coal – in an effort to 

limit impacts on high-sulfur coal producers (Ellerman et al 2000, pp. 301-2); (2) lack of information 

about marginal abatement costs on the part of market participants, particularly in the early years; (3) state 

regulation that, particularly in the early years of the program, had the effect of distorting or constraining 

utilities’ responses to federal environmental regulation (Arimura 2002; Bohi and Burtraw 1992; Ellerman 

et al 2000, pp. 190-5); (4) interactions between the SO2 program and other federal regulations, such as 

New Source Review and New Source Performance Standards, which constrained the program’s 

operation; and (5) policy uncertainty when regulators and policy makers subsequently considered further 

reductions in the national SO2 cap, as we discuss later. 

The program can also be evaluated based on the geographic distribution of impacts. Most coalfired power plants were located east of the Mississippi, and model-based analyses predicted that the 

largest share of emissions reductions would come from the Midwest and East. There was some concern 

that emissions would end up disproportionately concentrated, and that this, combined with prevailing 

wind patterns, would result in “hot spots” of unacceptably high SO2 concentrations. Despite these 

concerns, however, the program did not generate significant hot spots (Ellerman et al. 2000, pp. 130-1; 

Swift 2004), though recent work (Muller and Mendelsohn 2009) suggests that the use of damage-based 

trading ratios, rather than a single allowance price, could have been welfare-improving. 
5

In sum, the SO2 allowance-trading system’s actual costs, even if they exceeded the cost-effective 

ideal for a cap-and-trade system, were much lower than would have been incurred with a comparable 

traditional regulatory approach, and the program’s goals were achieved with less litigation (and thus more 

certainty) than is typical for traditional environmental programs. There is broad agreement that the SO2

allowance-trading system provided a compelling demonstration of the advantages of a market-based 

approach to environmental protection. With this background on design and performance, we turn to four 

significant ironies. 

Doing the Right Thing for the Wrong Reason 

 In the years leading up to the enactment of the Clean Air Act Amendments of 1990, there was 

great concern in the United States about acid rain, in particular about the acidification of forests and 

aquatic ecosystems. Thus, the central purpose of the SO2 allowance-trading program was to reduce 

precursor SO2 emissions in order to reduce acid rain, primarily in the northeastern United States (National 

Acid Precipitation Assessment Program 1998). This was accomplished – SO2 emissions were 

dramatically cut. However, it turns out that the ecological benefits of the program have been relatively 

small – largely because it takes much longer than thought to reverse the acidification of ecosystems 

(National Acid Precipitation Assessment Program 2005) – while other, completely unanticipated benefits 

of the program have been massive. 

 Whereas some studies at the time of the program’s enactment predicted that its benefits would be 

approximately equal to its costs (Portney 1990), more recent estimates have pegged annual benefits at 

between $59 and $116 billion, compared with annual costs of $0.5 to 2 billion (Table 1). More than 95 

percent of these benefits are associated not with ecological impacts (including acidification of aquatic 

ecosystems), however, but with human health impacts of reduced levels of airborne fine sulfate particles 

less than 2.5 micrometers in diameter (PM2.5) derived from SO2 emissions. Epidemiological evidence of 

the harmful human health effects of these fine particulates mounted rapidly in the decade after the CAAA 

was enacted (Chestnut and Mills 2005). 

 Estimates of these health benefits vary widely, but they appear to be on the order of $50 billion to 

more than $100 billion per year (Burtraw et al. 1998; Burtraw 1999; Chestnut and Mills 2005; National 

Acid Precipitation Assessment Program 2005; Shadbegian, Gray, and Morgan 2005; U.S. Environmental 

Protection Agency 2011a). As Table 1 shows, strict ecosystem benefits are probably considerably less 

than program costs, though at least one study (Banzhaf et al 2006) suggests that ecosystem benefits alone 

have exceeded program costs. In any case, estimated human health benefits of the program have 

exceeded annual costs by a factor of more than fifty! The government did what turned out to be the right 

thing for the wrong reason. 

An Unanticipated Consequence of Deregulation 

In addition to being less costly than traditional command-and-control policies would have been, 

the realized costs of the SO2 allowance trading program were substantially less than ex ante forecasts 

prior to implementation (National Acid Precipitation Assessment Program 2005).2

 While part of this 

discrepancy was due to technological innovation and the speed with which the allowance market matured, 

a major factor in low realized compliance costs was the emergence of input substitution, from high to low 

sulfur coal, as a cost-effective compliance strategy. And, interestingly, the attractiveness of switching to 

 

2

 A revolutionary aspect of the cap-and-trade approach was that for the first time regulators had instantaneous 

information in a summary statistic (the allowance price) of the marginal cost of compliance, but the program’s 

design did not allow for any response to that information, such as changing the cap. 
6

low sulfur coal was increasing before the program even went into effect, due to a public policy change – 

unrelated to the environment – initiated long before the CAAA of 1990. 

Prior to 1976, the Interstate Commerce Commission (ICC) set rates for freight rail. Then, the 

Railroad Revitalization and Regulatory Reform Act of 1976 and the Staggers Rail Act of 1980 gave rail 

carriers the ability to set their own rates, and legalized private railroad-shipper contracts. The result was 

that shipping rates for coal (and other products) declined dramatically (Winston 2005; U.S. Government 

Accountability Office 2007). This brought with it a substantial fall in the cost of bringing coal from the 

Powder River Basin in Wyoming and Montana to centers of high demand east of the Mississippi River, 

relative to the costs of coal from the Midwest and Appalachia (Ellerman et al. 2000) – even though the 

existence of only two major rail lines kept shipping costs above competitive levels (Busse and Keohane 

2008). 

The three major coal deposits in the United States are located in the Powder River Basin (PRB), 

the Illinois Basin and Central Appalachia. Of these, PRB coal is cheapest to mine and has the lowest 

sulfur content, though considerable low-sulfur coal was also produced in the East, particularly after the 

acid rain program took effect. Hence, absent the use of any abatement technology, switching from highsulfur eastern coal to low-sulfur coal, particularly PRB coal, reduces power plant SO2 emissions per unit 

of electricity generation. 

The majority of coal-fired power plants in the United States are located along or east of the 

Mississippi River, making PRB the most distant option for major sources of demand. As freight prices 

fell with deregulation, liberalization gave freight carriers flexibility and incentive to contract with eastern 

utilities, and these same utilities developed low-cost ways to modify their boilers (which were designed to 

burn bituminous coal) to burn sub-bituminous PRB coal (Ellerman et al 2000, pp. 243-45). The average 

sulfur content of coal burned at electric generating units began to fall. In fact, SO2 emissions at units 

covered by the allowance-trading program were actually falling from 1985 to 1993, before the acid rain 

program took effect (Ellerman and Montero 1998). The main source of this decline was the increased use 

of PRB coal, with average rail rates of shipping PRB coal to Midwest generators falling by over 50 

percent from 1979 to 1993 (Gerking and Hamilton 2008). 

 For some power plants, this made fuel-switching from high-sulfur to low-sulfur coal costeffective even in the absence of the acid rain legislation; and for many other eastern power plants, it made 

fuel-switching less expensive than installing scrubbers in response to the legislation. Of the 263 units 

regulated in the first phase of the allowance-trading program, 52 percent primarily pursued fuel switching 

or blending low-sulfur coal with higher-sulfur coal, accounting for 59 percent of emissions reductions; 

and scrubbers were installed at about 10 percent of the units, accounting for 28 percent of emissions 

reduction (U.S. Energy Information Administration 1997).3

 Overall, it appears that about one-third of 

SO2 emissions reductions in the early years of the program were due to prior railroad deregulation and 

two-thirds to the SO2 allowance trading program (Ellerman et al. 2000, p. 122). 

 It could be argued that because these reductions in delivered fuel costs would have occurred in 

the absence of the SO2 allowance trading program — and would have reduced the costs of a commandand-control SO2 program as well — the cost savings attributed to the SO2 allowance-trading program

(relative to a command-and-control system) should be adjusted downward (Carlson et al. 2000). This is 

valid, but it is also true that a prescriptive regulatory approach – such as a policy that required the 

installation of scrubbers at all power plants – might have prevented electricity companies from taking 

advantage of some of these alternative compliance options. 

 

3

 In addition, 32 percent of the units complied by obtaining additional allowances as well as switching to lowersulfur coal, accounting for 9 percent of emissions reductions; 3 percent of the units were retired, accounting for 2 

percent of emissions reductions; and 3 percent of the units used other compliance methods, accounting for 2 percent 

of emissions reductions (U.S. Energy Information Administration 1997). 
7

 In any event, it is clear that significant shares of the emissions reduction – about one-third in the 

early years – and of the cost savings associated with the SO2 allowance trading system were actually an 

unanticipated consequence of an earlier, unrelated public policy change. 

Conservatives Demonize Their Own Innovation 

 Some two decades after the Clean Air Act Amendments of 1990 were signed into law by 

President George H. W. Bush, the U.S. House of Representatives passed legislation – H.R. 2454, the 

American Clean Energy and Security Act of 2009 or the Waxman-Markey bill – that included an 

economy-wide cap-and-trade system to cut carbon dioxide (CO2) emissions linked with global climate 

change. But, one year later, in July of 2010, the U.S. Senate abandoned its attempt to pass companion 

legislation. 

In the process of considering this legislation, conservative Republicans (and some coal-state 

Democrats) attacked the cap-and-trade system as “cap-and-tax.’’ They may have been helped by 

President Obama’s January 2009 budget message to Congress, which provided for revenues from an 

auction of 100 percent of the allowances under such a scheme (Chan, Stavins, Stowe, and Sweeney 2012). 

Regardless of what they thought about climate change, there was significant irony to this demonization of 

market-based approaches to environmental protection, since these policies were innovations developed by 

conservatives in the Reagan, George H. W. Bush, and George W. Bush administrations – and once 

strongly condemned by liberals and environmentalists. 

 In the 1980s, President Ronald Reagan’s Environmental Protection Agency put in place a trading 

program to phase out leaded gasoline. It produced a more rapid elimination of leaded gasoline from the 

marketplace than had been anticipated, and at a savings of some $250 million per year, compared with a 

conventional no-trade, command-and-control approach (Stavins 2003). Not only did President George H. 

W. Bush successfully propose the use of cap-and-trade to cut U.S. SO2 emissions, his administration 

advocated in international fora the use of emissions trading to cut global CO2 emissions, a proposal 

initially resisted but ultimately adopted by the European Union. In 2005, President George W. Bush’s 

EPA issued the Clean Air Interstate Rule, aimed at reducing SO2 emissions by a further 70 percent from 

their 2003 levels. Cap-and-trade was again the policy instrument of choice in order to keep costs down 

and achieve rapid reductions at minimum economic pain. (This rule was later invalidated by the courts, as 

we discuss below.) 

 When the CAAA was being considered in the U.S. Congress, environmental and energy debates 

typically broke along geographic lines (with key parameters being degree of urbanization and reliance on 

specific fuel types, such as coal versus natural gas). Support and opposition were both largely bipartisan. 

The CAAA passed the Senate in 1990 by a vote of 89-11 with 87 percent of Republican members and 91 

percent of Democrats voting yea, and it passed the House of Representatives by a vote of 401-21 with 87 

percent of Republicans and 96 percent of Democrats voting in support. 

Such bipartisan voting patterns were typical for environmental issues in the 1970s through much 

of the 1990s. But by the time climate change legislation received serious consideration in Washington in 

2009-2010, environmental politics – and partisan politics more generally – had changed dramatically, 

with Congressional voting on environmental legislation typically taking place along strictly partisan lines. 

The Waxman-Markey legislation was passed by the House of Representatives in 2009 by a vote of 219-

212, with support from 83 percent of Democrats, but only 4 percent of Republicans. 

 This polarization between the two political parties on environmental issues (Shipan and Lowry 

2001) was (and is) part of a gradual widening gulf between the parties on virtually all issues (Fleisher and 

Bond 2004). The polarization has shown up in studies by political scientists employing a diverse set of 

measures that place members of Congress on an ideological spectrum from extreme right to extreme left 
8

based on their roll-call votes (Poole and Rosenthal 1997, 2007). Polarization – the gradual disappearance 

of moderates – has been taking place for decades (Lowry and Shipan 2002; Theriault 2008). The rise of 

the Tea Party movement within the Republican Party is only the most recent episode in a much longer 

story. 

 Four structural factors have been considered as possible contributors to this trend. First, there has 

been the increasing importance of the primary system, a consequence of the “democratization” of the 

nomination process that began in the 1970s (Bartels 1988, Ansolabehere, Snyder, and Stewart 2001). A 

small share of the electorate vote in primaries, namely those with the strongest political preferences: the 

most conservative Republicans and the most liberal Democrats (Burden 2001). This self-selection favors 

candidates from the extremes (King, Orlando, and Sparks 2011). Second, decades of redistricting have 

produced more and more districts that are dominated by either Republican or Democratic voters (Carson, 

Crespin, Finocchiaro, and Rohde 2007; Ansolabehere and Snyder 2002), which further increases the 

importance of primary elections. Third, geographic sorting of like-minded households may have furthered 

this trend. Fourth, the increasing cost of electoral campaigns greatly favors incumbents (Carson, 

Engstrom, and Roberts 2007), with the ratio of average incumbent-to-challenger financing now exceeding 

10-to-1. This tends to make districts relatively safe for the party that controls the seat, thereby further 

increasing the importance of primaries. 

 These factors operate mainly when new members of Congress are elected (Theriault 2006). To a 

lesser degree, polarization has also taken place through the adaptation of sitting members of Congress: in 

order to discourage or survive primary challenges, Republican members shift rightward and Democratic 

members shift leftward. A striking recent example of this shift is the evolution of Senator John McCain, 

Republican of Arizona, from a moderate during his 2008 Presidential run to a solid conservative in 2010 

in response to a primary challenge from a Tea Party candidate. 

 The Great Recession of the past several years, like the Great Depression of the 1930s, has 

undoubtedly increased political polarization (McCarty, Poole, and Rosenthal 2006). The 1930s saw not 

only the rise of American socialists and communists, but also the rise of American right-wing extremism. 

It may be that better economic times will reduce the pace of political polarization. However, in the face 

of the long-term structural factors noted above, it is difficult to be optimistic about the long-term 

prognosis. 

 Many conservatives in the Congress undoubtedly opposed climate policies because of 

disagreement about the threat of climate change or the costs of the policies, but instead of debating risks 

and costs, they chose to launch an ultimately successful campaign to demonize and thereby tarnish capand-trade as an instrument of public policy, rendering it “collateral damage” in the wider climate policy 

battle. This scorched-earth approach could come back to haunt conservatives if future environmental 

initiatives with widespread support are enacted without making use of the power of the marketplace to 

reduce compliance costs. It is ironic that conservatives chose to demonize their own market-based 

creation. It is perhaps even more ironic that this tactic seems to have been effective despite their 

creation’s excellent performance. 

What the Government Gives, It Can Take Away 

 A major source of uncertainty about any government-created market is that the government can 

undo what it created — possibly unintentionally. In essence, this is what has happened in the SO2

allowance market. 

 Prices for SO2 allowances were remarkably stable throughout the program’s first decade (Figure 

1). But in 2004, prices began to rise, ultimately topping $1,200/ton in 2005. Why did this happen? It 

was widely recognized by the late 1990s that SO2 reductions in excess of those resulting from the trading 
9

program of Title IV would be required by other provisions in the Clean Air Act and would in any event be 

warranted, given the significant adverse health effects of fine particulates associated with SO2 emissions. 

But Title IV did not give EPA authority to adjust the program, such as by tightening the overall cap, in 

response to new information about the benefits (or costs) of emissions reductions. This led to a chain of 

events that ultimately brought about the virtual collapse of the SO2 allowance trading program. 

 In early 2002, President George W. Bush proposed the Clear Skies Act, which would have greatly 

tightened the SO2 cap. The lack of an initial allowance market reaction suggests it was no surprise when 

this proposal died in March 2005, having failed to move out of committee. The Administration then 

promulgated its Clean Air Interstate Rule (CAIR) in May, 2005, with the same purpose of lowering the 

cap on SO2 emissions (to 70 percent below the 2003 emissions level). CAIR did this in part by applying 

more stringent emission requirements on states that were contributing to violations of EPA’s primary 

ambient air quality standards for fine particulates in the eastern United States (Palmer and Evans 2009). 

It required sources within those states to surrender two additional allowances for every ton of SO2

emissions, effectively reducing the cap by two-thirds. Because CAIR provided that firms could bank 

their SO2 allowances for use in the new program, prices rose further in anticipation of CAIR’s more 

stringent cap, with spot prices increasing from $273 per ton in EPA’s 2004 auction to $703 in the 2005 

auction (Figure 1).4

 After peaking in 2005 at more than $1,200 per ton, SO2 allowance prices dropped just as fast as 

they had risen, aided by EPA’s announcement that it would re-examine CAIR (Samuelsohn 2005) and 

speculation about impending legal challenges (Samuelsohn 2006a; Kruse 2009).5

 The speculation was 

proven to be correct on June 26, 2006, when North Carolina and other states and a number of utilities 

sued EPA over CAIR (Samuelsohn 2006b). The states argued that the interstate trading allowed under 

CAIR was inconsistent with a provision in the Clean Air Act that obliges each state to prevent emissions 

that interfere with any other state’s attainment or maintenance of air quality standards. 

Two years later, on July 11, 2008, the Circuit Court of Appeals for the District of Columbia 

responded to the lawsuit by vacating CAIR in its entirety, and thereby invalidating the core of prior SO2

regulation, the cap-and-trade system with unlimited trading across states, by asserting that under the 

Clean Air Act EPA did not have authority to ignore the relationship between sources and receptors (U.S. 

Environmental Protection Agency 2011a). On that single day, the SO2 allowance price fell from $315 to 

$115 (Figure 1) (Burtraw and Szambelan 2009). The Bush administration – and the subsequent Obama 

administration – chose not to appeal that ruling. In December, the court allowed CAIR to remain in effect 

while EPA devised a replacement that addressed its concerns, but it remained clear that unlimited 

interstate trading was doomed. Expectations of a more stringent SO2 cap, which had fueled the run-up in 

allowance prices, became less defensible, and prices continued to fall, returning to the range of their pre-

 

4

 An array of other factors contributed to the run-up and eventual spike in SO2 allowance prices, including: 

Hurricanes Katrina (August, 2005) and Rita (September 2005), which impaired petroleum refining and natural gas 

capacity. In addition, delivery of low-sulfur coal from the Powder River Basin to Midwestern power plants was 

disrupted by track failures (May, 2005) on both the Union Pacific and Burlington Northern Santa Fe railroads, which 

caused low-sulfur coal prices in the Midwest to peak in December, 2005, at a level three times greater than a year 

earlier. This led some power companies to switch to higher sulfur coal from the east, increasing demand for SO2

allowances. A final factor was features of the allowance trading program’s design that interacted with the tax 

system and utility regulation to restrict the number of allowances actually available for trading at any time (the 

“float”), thus compounding the price impacts of the other factors (Parsons, Ellerman, and Feilhauer 2009). 

 

5

 Also contributing to the fall in allowances prices from their peak was a drop in natural gas prices, the restoration 

of refining and gas capacity in the Gulf of Mexico following Hurricanes Katrina and Rita, and the realization of a 

likely adequate supply of allowances and installed scrubber capacity to comply with CAIR (Burtraw and Szambelan 

2009). In addition, the expectation of an economy-wide CO2 cap-and-trade system, which all three major 

Presidential candidates – John McCain, Hilary Clinton, and Barak Obama – in 2007 supported, would have led to an 

exogenous, long-run decline in SO2 emissions as well, and hence to a decline in the value of banked allowances. 
10

2004 levels. At EPA’s 2009 auction, spot allowances (which could be used in 2009 or later) sold for $70 

per ton, compared with $390 a year earlier (Burtraw and Szambelan 2009). 

 In July, 2010, the Obama Administration proposed its Clean Air Transport Rule (CATR) to limit 

annual SO2 (and NOx) emissions in 28 states, as a replacement for the CAIR. The proposed rule 

established state-specific emissions caps for power plant SO2 emissions, limiting inter-state trading. The 

rule was finalized in July, 2011, as the Cross-State Air Pollution Rule (CSAPR), allowing only intrastate 

trading and limited trading between two groups of states. (Predictably, this rule has also been challenged 

in court, by 27 states and 18 other parties, and in January 2012 the D.C. Circuit Court ordered EPA to 

keep CAIR in force pending its review of CSAPR.) 

The shift from CAIR to CSAPR was the death-knell for the SO2 allowance trading program, 

though the program remains nominally in place, since it dramatically reduced the scope for cost-effective 

interstate trades. The SO2 market collapsed, with allowance prices falling to record low levels. By the 

time of EPA’s 2012 auction, market-clearing prices had fallen to $0.56 in the spot auction and $0.12 in 

the seven-year advance auction.6

In essence, the imposition of state-level and source-specific prescriptive regulation has all but 

eliminated the demand for allowances. States with binding caps under CSAPR have no alternative but to 

reduce their emissions, whether by mandating the use of scrubbers, retiring coal-fired power plants, or 

setting up intrastate trading. Either way, the demand for federal SO2 allowances has been virtually 

eliminated. 

 

While the SO2 allowance market functioned effectively, the broader regulatory environment 

served to end its life prematurely. (One more irony: the program’s success may have weakened the case 

for continuing the allowance market by reducing the heterogeneity of abatements costs across sources, 

thus reducing potential gains from trade (Newell and Stavins 2003).) When the government creates a 

market, it can also destroy it, possibly fostering a legacy of increased regulatory uncertainty and reduced 

investor confidence in future cap-and-trade regimes, and hence reduced credibility of pollution markets 

more broadly. 

Conclusions 

 More than twenty years after the Clean Air Act amendments of 1990 launched the path-breaking 

SO2 allowance trading system, the world’s first large-scale market-based environmental initiative, that 

grand experiment in public policy continues to enjoy its reputation around the world as a great success. 

Although it is true that the system performed at least as well as its optimistic advocates had anticipated 

through its first decade of operation – reducing emissions cost-effectively – it is also true that reflecting 

now on this performance yields a considerably more nuanced assessment. 

 Although the emissions-reduction cap was indeed achieved, the program had originally been 

intended to reduce damages to forests and aquatic ecosystems caused by acid rain, and the system has 

accomplished considerably less in that regard than had been anticipated. At the same time, however, 

actual costs of compliance have been substantially less than originally expected. Even more striking is 

that the real benefits of the program are both much greater than its costs and very different in kind from 

those that were anticipated. Rather than providing significant ecological benefits, reductions in SO2

emissions under the allowance trading system have resulted in dramatic decreases in downwind 

 

6

 When new Mercury and Air Toxics Standards (MATS) affecting coal-fired power plants take effect – likely in 

2015-2016 – they will likely be so stringent that SO2 constraints under CSAPR will be rendered non-binding in one 

of the two SO2 trading zones. Further, the MATS explicitly do not allow trading, and so assuming these rules are 

finalized and implemented as expected, there will be only a minimal market for SO2 (Burtraw, et al. 2012). 
11

concentrations of small particulates, thereby producing great benefits to human health, particularly 

reductions in mortality. Hence, it is fair to say that the government did what turned out to be the right 

thing for the wrong reason. 

 Despite the worldwide celebration of the success of this cap-and-trade system, it now appears that 

some part of that success in reducing SO2 emissions at low cost was due not to allowance trading but to 

the earlier deregulation of U.S. railroads. This reduced the delivered cost of low-sulfur coal from the 

Powder River Basin to the Midwest, and so provided economic incentives for substitution of this “clean 

coal” for the high-sulfur coal mined in the eastern part of the country. A significant share of the SO2

emissions reductions associated with the CAAA was actually an unintended consequence of other, nonenvironmental policy innovations, and the availability of this low-cost compliance option was a major 

factor in the system’s cost-effectiveness. 

 Market-based systems, such as cap-and-trade, would seem to be a quintessential Republican 

approach to environmental protection. Indeed, history has validated this, with Ronald Reagan’s lead 

trading system at the heart of his phasedown of leaded gasoline in the 1980s, George H. W. Bush’s SO2 

allowance-trading system and international advocacy of cap-and-trade in the 1990s, and George W. 

Bush’s Clear Skies proposal and Clean Air Interstate Rule in the current century. But more recent history 

and politics surrounding potential public policies to reduce CO2 emissions linked to global climate change 

have exhibited a very different pattern. With political polarization having reached high levels, the 

environment is no longer a regional, bipartisan issue in Washington, but a decidedly and decisively 

partisan one, with conservatives – largely Republicans – coming to be strongly opposed to national 

climate legislation. In the process of opposition, they have demonized cap-and-trade proposals as “capand-tax” and have thereby tarnished this market-based approach to environmental protection. If the 

tarnish cannot be removed, the cost of future environmental programs may be needlessly increased. 

 Ironically, an attempt to render more stringent the government’s SO2 emissions cap through the 

use of a separate, but related cap-and-trade system eventually led through a series of court cases and 

regulatory responses to the virtual closure of the SO2 allowance market. Because of increasing concerns 

about the human health impacts of fine particles, the George W. Bush administration included SO2 targets 

in its multi-pollutant Clear Skies legislation in 2002. The Congress failed to act on the legislation, and so 

the Bush administration instead proposed tightening the CAAA cap in its Clean Air Interstate Rule or 

CAIR, in 2005. That approach was invalidated by the courts in 2008, because it did not prevent interstate 

transmission of pollution, and the Obama administration’s proposed replacement, finalized in 2011 as the 

Cross-State Air Pollution Rule, would virtually eliminate interstate trading, the source of most of the 

potential gains from trade. As a result, the SO2 allowance trading system has essentially come to an end. 

What the government gives, it can take away. 

 What are the implications of this history of the SO2 allowance trading program for future 

environmental policy, including for climate change? The good news, which this program clearly 

demonstrated, is that cap-and-trade is not just a subject of seminars and journal articles; it is a viable 

option for tackling large-scale environmental problems. Even if the SO2 allowance trading program’s 

performance was enhanced by unanticipated benefits and declines in coal prices, and even if it has been 

essentially wiped out by later policy changes, the fact is that the allowance trading program achieved its 

target emissions reductions rapidly and cost-effectively. Few other environmental programs of any sort 

have performed as well. 

 The bad news is that “cap-and-tax” rhetoric may make it hard to use this approach in the U.S. to 

deal with climate change. This is bad news indeed. Emissions of CO2 from coal-fired power plants will 

no doubt be reduced by EPA rules on SO2, NOx, mercury, coal fly-ash, and cooling-water withdrawals 

that are working their way through the regulatory process, and that will drive up the cost of generating 

electricity with coal. But these rules, and those likely to be adopted by the EPA in response to the 

requirement that it regulate CO2 under the Clean Air Act, are unlikely to be cost-effective policies for 
12

reducing greenhouse gas emissions. At a time when environmental protection in general and climate 

policy in particular have become highly polarized in the U.S. Congress, the outlook for an efficient and 

effective national climate policy is not good. In particular, the tarnishing of cap-and-trade by 

conservatives as a potential instrument of action may make it even more difficult to give serious 

consideration in the future to this and other market-based approaches to environmental protection. 

 

 We thank Richard Sweeney for research assistance, and Dallas Burtraw, Denny Ellerman, Juan-Pablo 

Montero, Sean Theriault, and Tom Tietenberg for valuable comments on a previous version of this paper. Any 

errors and all opinions are our own. 

 
13

Table 1: Estimated Annual U.S. Benefits and Costs of the SO2 Allowance Trading 

Program; Title IV, Clean Air Amendments of 1990 

(Billions of U.S. 2000 Dollars) 

Source: Burtraw et al. (1998); Burtraw (1999); Chestnut and Mills (2005); Banzhaf et al. (2006). 

 

Benefits 

 

Mortality $ 50 – 100

Morbidity 3 – 7

Recreational Visibility 2 – 3

Residential Visibility 2 – 3

Ecosystem Effects 0.5

Total Annual Benefits 59 – 116

Costs 0.5 – 2.0

Net Benefits 58 – 114
14

Figure 1: SO2 Allowance Prices and the Regulatory Environment, 1994-2012

(1995 $ per ton) 

Source: Data on spot prices compiled by Power & Energy Analytic Resources (PEAR) Inc. from Cantor Fitzgerald 

until September 11, 2001, and from ICAP United thereafter. 

0

200

400

600

800

1000

1200

1400

8/94 8/96 8/98 8/00 8/02 8/04 8/06 8/08 8/10

Phase II Begins

CAIR Finalized

CAIR

Vacated

Clear Skies 

Announced

Train Derailments Reduce 

PRB Coal Deliveries

Hurricane Katrina

Hurricane Rita

CSAPR 

Announced

CATR

Proposed

CAIR Remanded

to EPA

EPA Announces It Will 

Re-Examine CAIR

North Carolina Sues EPA
15

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