This was a particularly tricky issue, because the health and environmental impacts from increased greenhouse gas concentrations are indirect, as opposed to pollutants like ozone, which directly harm living organisms or sulfur dioxide, which acidifies lakes and streams. Nevertheless, in 2009 the EPA issued just such an "endangerment finding", opening the door for direct regulation should Congress fail to pass legislation reducing greenhouse gas emissions.
Now, five years after the original Supreme Court ruling, the EPA is finally preparing to exercise its authority to regulate emissions from power plants. The agency is expected today to issue New Source Performance Standards that limit carbon dioxide emissions from newly constructed power stations to 1,000 pounds per megawatt-hour of generation. For those more accustomed to metric units, that's about 0.45 tonnes CO2/MWh. A combined cycle natural gas power station can have emissions below 0.40 tonnes CO2/MWh and so is not likely to be affected by this regulation.
Other fossil fuels will face greater challenges. If the rule stands, it means no new traditional coal-fired power plants will be built in the United States. A typical coal-fired power station releases can release 0.90 tonnes CO2/MWh, or more. To operate within the New Source Performance Standards, such a plant would have to generate half its power with renewable biomass fuels (physically possible for no more than a handful of power stations). Otherwise they would need to employ carbon capture and storage (CCS) - a technology that may yet take decades to beome commercially viable - to bury the CO2 deep underground.
The EPA's New Source Performance Standards would grandfather existing power stations, and allow them to keep operating and undergo retrofitted even if they exceed the emissions thresholds. However, they still serve a useful purpose by setting a timeline for the gradual phaseout of these plants. A power station can operate for 50 years or more, so the investment decisions we make now lock us into a decades-long emissions path.
When it comes to climate change, we're already at the bottom of a deep hole. The EPA's new ruling is a signal to power plant operators that we need to stop digging.
