The use of executive powers to regulate greenhouse gas emissions has been reaffirmed by the US Supreme Court in arulingissued on Monday. We take a look at the history of US efforts to regulate emissions and what the latest ruling means for the future.

First, here’s a brief timeline of US efforts to tackle greenhouse gas emissions.

2003, 2005, 2008 and 2010

Between 2003 and 2010 the US Congress repeatedly tried andfailedto pass cap-and-trade legislation that would have limited emissions across the US economy.

The number of climate lawsreaching Congresspeaked in 2009-10, as the chart below shows. The current Congress still has until mid-term elections in November to catch up.

Source:Center for Climate and Energy Solutions

The 112th US Congress during 2011-2012 was the first to make no attempt to pass cap-and-trade rules since the first effort, way back in 2003. Obama has effectivelygiven upon getting Congress to act and is using the executive powers of the USEnvironmental Protection Agencyinstead.

2007

The EPA’s executive powers to regulate greenhouse gas emissions stem from a 2007 Supreme Courtruling。这说尼克松时代的Clean Air Act should be used to regulate “any pollutant” that “endangers public health or welfare”. This case is often referred to as Massachusetts vs EPA.

2009

In 2009 the EPA produced a210-page reportto support its “endangerment finding” that greenhouse gas emissions are indeed a threat to public health. This triggered a requirement to issue greenhouse gas regulations under the Clean Air Act.

2010 and 2011

The EPA issued regulations covering tailpipe emissions fromcars, vansandtrucksin 2010 and 2011. In 2010 it also issued afinal noticeof its intention to regulate emissions from stationary sources such as factories and power stations. This is what Monday’s Supreme Court decision ruled on.

The EPA haddecidedstationary sources emitting more than 100,000 tonnes of carbon dioxide per year should be required to obtain a permit to operate. They should also be required to apply the best available control techniques (BACT) to limit emissions.

2012 and 2013

Subsequently the EPAproposedlimits for greenhouse gas emissions from new power plants. The limits would effectively ban additional coal-fired capacity without carbon capture and storage facilities.

The rules have yet to enter force having been subject to extensive consultation and legal challenge. EPAissuedrevised rules in 2013. These are supposed to be finalised in January 2015.

2014

In May this year the EPAissuedplans to limit emissions from existing power plants. The ‘Clean Power Plan’ rules are due to be finalised in June 2015. We’ve already taken adetailed lookat the proposals.

A key point is that they would extend EPA jurisdiction beyond the fenceline of power plants, out into the wider economy. This is designed to give states maximumflexibilityto comply through energy efficiency or renewables, for instance, but it is a legal weak link.

Legal challenges

The EPA’s endangerment finding waschallenged, and in 2012upheld。The Supreme Court has denied a review of this decision.This week’s Supreme Court ruling stems from a series ofcaseschallenging EPA regulation. It ruled on six separate cases in a single decision.

It considered just two questions: does the Clean Air Act compel the EPA to require permits for stationary sources of greenhouse gases and should permitted sites be required to apply BACT to limit emissions.

《清洁空气法》规定允许适用于emissions of 250 tonnes or more. For greenhouse gases this would cover tens of thousands of sites, making the rules impossibly burdensome to enforce.

The EPA solution was to “tailor” the threshold to 100,000 tonnes of greenhouse gases. The Supreme Court struck this down. The EPA had no authority to rewrite the limits written into law by Congress, it said.

The legal debate centred on the meaning of “any pollutant”. Should this cover all pollutants or should EPA take a pragmatic, context-specific decision on which pollutants to include?

The court ruling favoured the latter. It is written in language highlycriticalof the EPA’s inclusive, “all pollutants” approach, which it said took “some cheek” given the EPA has shown pragmatism elsewhere. The ruling also contains clearwarningsagainst attempts to expand the EPA’s regulatory reach.

But the court backed EPA’s right to regulate greenhouse gas emissions from sites already covered by the Clean Air Act because of emissions of other pollutants. That leaves the EPA able to target 83 per cent of stationary source greenhouse gas emissions, only slightly lower than the 86 per cent it wanted to target.

It’s also important to note that the EPA’s power plant rules are based on a different section of the Clean Air Act, so there is no direct legal impact on them from Monday’s ruling.

Solid foundations

The latest ruling affirms the legal basis of the EPA’s regulatory efforts, namely Massachusetts vs EPA. The court had the chance to revisit that decision but chose not to.

Two of the nine Supreme Court justices repeated their view that the 2007 ruling was wrong. But the other seven judges did not question its validity and showed no willingness to look at it again.

The Supreme Court is in general reluctant to challenge its own past decisions,according toCase Western Reserve University School of Law Professor Jonathan H. Adler.

That means Massachusetts vs EPA is “here to stay”, Adler writes. Even lawyers for the US power sectorconceded its validityduring earlier hearings. EPA regulation of emission is here to stay too, says Adler.

So President Obama’s climate policy has solid legal foundations.

A Congressional rewrite of the Clean Air Act could shake those foundations. But there do not appear to be any serious expectations this could happen. Congressional inability to agree on climate laws is the reason the Clean Air Act is being used in the first place.

Even so, further legal challenge to Obama’s power plant plans are inevitable. This will mean the rules are delayed by five years until around 2020, according to ablogfor thinktank the Brookings Institution.

Despite the lack of a direct legal link commentators have alreadystartedpickingoverthe entrails of Monday’s Supreme Court decision for signs of how it might rule if, or perhaps more likely when, the power plant rules are challenged.

The court’s warning against EPA expanding its regulatory reach is key here. Its power plant rules imply regulating not just power plants but other aspects of the economy.

The court ruling says:

“When an agency claims to discover in a long-extant statute an unheralded power to regulate ‘a significant portion of the American economy’… we typically greet its announcement with a measure of skepticism. We expect Congress to speak clearly if it wishes to assign an agency decisions of vast ‘economic and political signifiÂcance’.”

That seems to suggest the court would take a dim view of EPA overreach. The EPA has already anticipated this and has designed its power plant rules to resist attackaccordingto Brian H. Potts, partner at US law firm Foley & Lardner.

Potts writes:

“For example, if a court found that EPA’s renewable or energy efficiency assumptions were unlawful, the rule would just unravel a bit; it wouldn’t come completely undone.”

So while it seems unlikely that Obama’s power plant emissions controls will arrive on schedule – and that could have implications for UN climate talks in Paris next December – it would be a brave move to bet against them taking effect eventually.