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Supreme Court Decision Paves Way for Federal Regulation of Greenhouse Gas Emissions from Vehicles

The Supreme Court’s decision in Massachusetts v. EPA today (earlier post) may prove to be a landmark in the movement toward national regulation of greenhouse gas emissions from mobile as well as stationary sources. In the majority decision, the Supreme Court held that carbon dioxide and greenhouse gases are pollutants can be regulated under the Clean Air Act, and that as such the Environmental Protection Agency has the authority to set regulatory standards for greenhouse gas emissions from motor vehicles.

The Court ordered the EPA to reconsider its earlier decision not to regulate greenhouse gases, and to ground its arguments in the Clean Air Act.

The case originated when a group of private organizations petitioned the Environmental Protection Agency (EPA) to begin regulating greenhouse gases, including carbon dioxide, under the Clean Air Act. The Clean Air Act requires that the EPA establish “standards applicable to the emission of any air pollutant from any class of new motor vehicles which...cause[s], or contribute[s] to, air pollution reasonably anticipated to endanger public heath or welfare.

EPA denied the petition, reasoning that:

  1. The Clean Air Act does not authorize it to issue mandatory regulations to address global climate change, and

  2. Even if it did have the authority to set greenhouse gas emission standards, it would have been unwise to do so at that time because a causal link between greenhouse gases and the increase in global surface air temperatures was not unequivocally established.

The EPA also characterized any theoretical regulation of greenhouse gas emissions from motor vehicles as a piecemeal approach to climate change that would conflict with the Administration’s non-regulatory approach to encouraging reduction, among other factors.

The original petitioners, joined by Massachusetts and other state and local governments, sought review of the decision in the DC Circuit, which denied review in a 2-1 decision. The case moved to the Supreme Court, and was heard 29 Nov 2006. In the 5-4 decision today, the Court held that:

  1. The Petitioners do in fact have standing to challenge the EPA’s denial of the rulemaking petition.

  2. The harms associated with climate change are serious and well recognized.

    Indeed, the NRC Report itself, which EPA regards as an objective and independent assessment of the relevant science, identifies a number of environmental changes that have already inflicted significant harms, including the global retreat of mountain glaciers, reduction in snow-cover extent, the earlier spring melting of rivers and lakes, [and] the accelerated rate of rise of sea levels during the 20th century relative to the past few thousand years ...

  3. EPA’s failure to dispute the existence of a causal connection between man-made greenhouse gas emissions and global warming, its refusal to regulate such emissions, at a minimum, “contributes” to Massachusetts’ injuries. EPA overstates its case in arguing that its decision not to regulate contributes so insignificantly to petitioners’ injuries that it cannot be haled into federal court, and that there is no realistic possibility that the relief sought would mitigate global climate change and remedy petitioners’ injuries, especially since predicted increases in emissions from China, India, and other developing nations will likely offset any marginal domestic decrease EPA regulation could bring about.

    ...EPA overstates its case. Its argument rests on the erroneous assumption that a small incremental step, because it is incremental, can never be attacked in a federal judicial forum. Yet accepting that premise would doom most challenges to regulatory action. Agencies, like legislatures, do not generally resolve massive problems in one fell regulatory swoop...They instead whittle away at them over time, refining their preferred approach as circumstances change and as they develop a more-nuanced understanding of how best to proceed.

    That a first step might be tentative does not by itself support the notion that federal courts lack jurisdiction to determine whether that step conforms to law.

    And reducing domestic automobile emissions is hardly a tentative step. Even leaving aside the other greenhouse gases, the United States transportation sector emits an enormous quantity of carbon dioxide into the atmosphere according to the MacCracken affidavit, more than 1.7 billion metric tons in 1999 alone. That accounts for more than 6% of worldwide carbon dioxide emissions.

    To put this in perspective: Considering just emissions from the transportation sector, which represent less than one-third of this country’s total carbon dioxide emissions, the United States would still rank as the third-largest emitter of carbon dioxide in the world, outpaced only by the European Union and China.  Judged by any standard, US motor-vehicle emissions make a meaningful contribution to greenhouse gas concentrations and hence, according to petitioners, to global warming.

  4. While regulating motor-vehicle emissions may not by itself reverse global warming, it does not follow that the Court lacks jurisdiction to decide whether EPA has a duty to take steps to slow or reduce it.

    Because of the enormity of the potential consequences associated with man-made climate change, the fact that the effectiveness of a remedy might be delayed during the (relatively short) time it takes for a new motor-vehicle fleet to replace an older one is essentially irrelevant. Nor is it dispositive that developing countries such as China and India are poised to increase greenhouse gas emissions substantially over the next century: A reduction in domestic emissions would slow the pace of global emissions increases, no matter what happens elsewhere.

  5. Despite an agency’s refusal to initiate enforcement proceedings not ordinarily being subject to judicial review, the Court held that it “may reverse [it if it finds it to be] arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law.

  6. Because greenhouse gases fit well within the Act’s capacious definition of “air pollutant,” EPA has statutory authority to regulate emission of such gases from new motor vehicles.

    Because EPA believes that Congress did not intend it to regulate substances that contribute to climate change, the agency maintains that carbon dioxide is not an air pollutant within the meaning of the provision. The statutory text forecloses EPA’s reading. The Clean Air Act’s sweeping definition of “air pollutant” includes “any air pollution agent or combination of such agents, including any physical, chemical ...substance or matter which is emitted into or otherwise enters the ambient air...§7602(g) (emphasis added). On its face, the definition embraces all airborne compounds of whatever stripe, and underscores that intent through the repeated use of the word “any.” Carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons are without a doubt “physical [and] chemical...substance[s] which [are] emitted into...the ambient air.”  The statute is unambiguous.

  7. EPA’s duty is to protect the public health and welfare, even if by setting standard in doing so, it overlaps with the responsibilities of other agencies.

    EPA finally argues that it cannot regulate carbon dioxide emissions from motor vehicles because doing so would require it to tighten mileage standards, a job (according to EPA) that Congress has assigned to DOT. But that DOT sets mileage standards in no way licenses EPA to shirk its environmental responsibilities. EPA has been charged with protecting the public’s “health” and “welfare,” a statutory obligation wholly independent of DOT’s mandate to promote energy efficiency. The two obligations may overlap, but there is no reason to think the two agencies cannot both administer their obligations and yet avoid inconsistency.

  8. EPA’s alternative argument for its decision—that even if it had authority to regulate greenhouse gases, the timing was not good—is “divorced from the statutory text” and is “impermissible.”Its action was “arbitrary, capricious, or otherwise not in accordance with law.” EPA must reconsider its decision, and ground its reasons for action or inaction in the Clean Air Act statute.

Justice Stevens delivered the opinion of the Court, in which Justices Kennedy, Souter, Ginsburg, and Breyer joined. Chief Justice Roberts filed a dissenting opinion, in which Justices Scalia, Thomas, and Alito joined. Justice Scalia also filed a dissenting opinion, in which Chief Justice Roberts and Justices Thomas and Alito joined.

Reaction from the Alliance of Automobile Manufacturers was somewhat muted. In a statement concerning the decision, Alliance president and CEO Dave McCurdy said:

The Alliance of Automobile Manufacturers believes that there needs to be a national, federal, economy-wide approach to addressing greenhouse gases.  This decision says that the US Environmental Protection Agency will be part of this process. The Alliance looks forward to working constructively with both Congress and the administration, including EPA and the National Highway Traffic Safety Administration, in developing a national approach.

The Alliance is one of the groups supporting the challenge in court to California’s law regulating motor vehicle greenhouse gas emissions.




Bravo. Now, of course, the EPA will drag its heels at least until Bush goes out of office.


We have opted for much stricter anti-smog regulation in the United States in terms of tailpipe emissions. This means that Europe gets much more efficient diesels and thus less CO2 emissions. Gasoline is much cleaner at the tailpipe, but less efficient in terms of fuel use.

The question in my mind is how the EPA would accomplish such regulation without causing economic damage. What's going to happen to my electric bill? How much is commuting going to cost me?


progressive taxes to encourage efficiency and alternatives would be a good start.

Robert Schwartz

anyone who thinks that this means anything in the real world is deluding himself. All it means is paperwork and lawsuits.

tom deplume

An Atkinson cycle would result in an engine that gets a lower SFC than diesels while having the lower emissions of gasoline. There is a power to weight penalty which could be overcome via hybrid technology. This is exactly Toyota's approach.


Robert S--

I disagree. California (along with other states) will now be free to enforce its laws limiting GHG emissions from automobiles. This is huge. Automakers just lost their argument that CO2 is not a pollutant.


I think this may help California in its case against the automakers no?


Yes, if this enables California to go ahead then it will be huge. I sense change in the air....and its not just CO2 levels.....


Given this ruling I think it's imperative that we need a national, consistent approach to this rather than piecemeal state-by-state regulatory nightmare.

This is going to be far, far harder and more expensive to accomplish than sulfur dixoide emissions and CFCs. Just watch the wrangling in Europe over Kyoto compliance and the failure of the Emissions Trading Scheme. We need a mass of new technologies that can economically replace fossil fuels as our primary energy source.

Remember that word: Economically.

Harvey D.


Economically - at all direct and indirect cost???

Plasma and LCD HDTVs sell by the millions even if they cost up to 5X the price of CRTs. The same applies to wireless VS wired phones.

Many pay 2x the price for a Laptop instead of a Desktop computer of equivalent or even lesser performance.

Many of us will not object to pay $5k to $10k more for PHEVs with sufficient electric range and/or BEVs to reduce oil consumption and pollution.

Lower initial purchase price is NOT and should NOT be the only driver. There are many other considerations.


Tom D.:  Diesels can use the same trick as the Atkinson cycle (greater expansion than compression ratio) too.  For some, all it would require is turbocompounding to turn the excess expansion energy into work.


Many of us will not object to pay $5k to $10k more for PHEVs with sufficient electric range and/or BEVs to reduce oil consumption and pollution.

The difference is that these early adopters are buying these products by choice. That is the key. It's the early adopters that finance making new technologies cheaper for everyone else, and they should be applauded for that. But being forced to use a certain technology despite significantly higher costs by government mandate is what worries me.


So let's slap a carbon tax on all fossil fuels and an Islamist-abatement tax on oil, which will be technology-neutral.


lower emissions of gasoline

This is entirely an artifact of legislation. ULSD will allow diesel exhaust to be treated for NOx and if gasoline engines go lean burn GDI (as they are trending) that exhaust treatment will also be needed for gassers. DPFs are effective enough that the PM count (all size fractions) after the DPF is lower than that for ambient air going into the engine and may be a good idea for gasoline engines as well (although you will still get secondary aerosols from fugitive emissions at fill time and distribution, especially from gasoline).


Once the Auto "Alliance" realizes that the cost of opposing the California standards exceeds the potential income - this decision will provide the authority needed for a national standard. Automakers now realize that spending money opposing standards for ICE is a long term net loss given the movement to PHEV and biofuels.

This landmark decision by States leader Massachusetts, will push the move to alternative energy transport systems faster. A good legal precedent. Congrats to MA.


I think this is a good ruling. Increased deaths from summer heat, and coastal flooding are just as real as increased deaths from smog damaged lungs. The court's urging of EPA to develop the groundworks of CO2 regulation should jarr the current administration's in-action on global warming.


Since the methods for reducing CO2 can take on many forms, if I were the automakers I would be promoting PHEVs, ethanol, biodiesel and give up on the E85 loophole trickery that has been going on.


Of those measures, the only one that doesn't have severe drawbacks is the PHEV, and Detroit seems to be afraid of them.  Some think it's because electric motors are far more reliable than engines, cutting into dealer repair profits.


If this can get the EPA and DOT to come together and reach a
consensus on transportation CO2 emissions then job well done.
It is remarkable that it takes the initiative of one state,
Massachusetts, to get non compliant Fedral bureaucracies to take
the ball and run with it. Hopefuly some progressive mandates
will phase out tail pipe emmissions in a verifiable fashion.
Keep an eye on the EPA as they have been huge enablers of the
particle emmission industry, weather it be industrial or



The FCC mandated ALL manufacturers AND importers can no longer sell any device with a TV receiver unless it has digital capability (VCRs, TVs, etc).

The digital tuners are far more expensive than the analog. So much for govt. regulations squashing the market.



Do you know how hard it is to find a CRT TV these days? Some retailers are phasing them out completely. And this before any mandate takes effect.

Oh, and that very same digital mandate has meant a billion dollar subsidy to provide digital tuners to people with analog TVs. So there is a very direct cost to the taxpayer already.

But we're not talking TVs, here. A TV is a much smaller investment compared to a new automobile.


EPA=Cheecky Bastards!!!

Sell out to Detroit and "the" others...

What a scam, what a shameful scam!


Shaun Williams

This is wonderful news. The world's biggest economy has legally declared greenhouse gases to be a pollutants.

For those afraid of a non-level playing field with developing nations, fear not, protectionism will be back with vengeance. They will have no choice but to fall into line if they wish to trade internationally.

The bottom line is, Mother Nature has given us a (nearly) free ride to prosperity for the last 200 years, it's time to use that advantage to move Humankind into the next "Age". Realistically, the developed nations are the only ones who can do this. Now, let's get (carefully) on with it...

Mark A

I guess this means the EPA must regulate cows, and their greenhouse emissions. And I guess eventually humans too. I am going out and buying "beano" stock right now.......

Hopefully this will speed development of ideas such as the Chevy Volt.


Tom Deplume - why do you say Atkinson gas engine delivers better SFC than diesel? Prius is still less efficient than VW TDI (approx 40% vs. 44%).

Engineer Poet - Atkinson cycle doesn't help diesel as much because there are no part throttle pumping losses to reduce. Detroit's 'fear' of PHEVs is the expense, not reliability. Modern engines last the life of the car, it's the other parts that wear out and/or get wrecked.

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