A historic moment for the Clean Air Act

In April 1974, a storm soaked Pitlochry, a small town in Scotland. It set a world record, not for rainfall but for pH: The rain was as acidic as vinegar. Sulfur dioxide pollution from coal-fired power plants had infiltrated clouds and fallen with the rain, dissolving into sulfuric acid. It was a dramatic illustration of a global problem. Acid rain killed fish in Northeastern U.S. lakes. It peeled paint and varnish from buildings. A 1986 Los Angeles Times story reported, "Even galvanized steel cannot escape destruction."

The problem was scary but solvable. Acid rain, along with urban smog and the deteriorating ozone layer, induced President George H. W. Bush to propose sweeping changes to the Clean Air Act that Congress passed in 1990 – the most thorough revision of the law since 1977, and a historic moment for environmental policy. The amendments included a bold policy experiment designed to slash sulfur-dioxide pollution – a market-based system now known as cap-and-trade. By 2012, emissions were down 80 percent. Acid rain is mostly a scourge of the past.

No administration has proposed an update of such magnitude since. Nevertheless, this June, when Environmental Protection Agency Administrator Gina McCarthy announced the first federal plan to limit carbon dioxide pollution from existing power plants, she signaled another watershed moment. The EPA's new "Clean Power Plan" would reduce carbon emissions on a state-by-state basis, averaging 30 percent below 2005 levels by 2030, to address an even more menacing global problem: man's fossil-fueled disruption of the climate.

"The plan is the last major thing that can be done under the existing Clean Air Act to control greenhouse gases," says Bill Pedersen, an attorney and air policy expert.

The coal industry will suffer some, and no doubt fight the cuts. Realistically, though, the EPA could no longer not regulate carbon dioxide. In 2003, after the Bush administration's EPA claimed the agency lacked the authority to regulate greenhouse gases under the Clean Air Act, a coalition of states, cities and environmental organizations sued. In 2007, the U.S. Supreme Court ruled in the states' favor, forcing the EPA to determine if greenhouse gases endangered human health and welfare. In 2009, the agency affirmed that they did, triggering a requirement to regulate them.

In a more functional world, Congress would have amended the act after the 2007 decision, giving the EPA a clear roadmap for controlling carbon, just as it did for sulfur dioxide and other pollutants. Congress could have established a carbon tax or nationwide cap-and-trade program. That would have been like taking the carpool lane to carbon reductions – fast and direct. Instead, the EPA was relegated to back roads with no phone signal, rife with potholes and detours, searching for a cost-effective, legal way to regulate carbon within existing law.

Each turn it made drew a lawsuit. The agency was sued by a coalition of industry groups, including coal, over the so-called "endangerment finding" and its legal authority to regulate carbon from cars, trucks and power plants, but prevailed. It was sued again over the "tailoring rule," an attempt to subject only the largest new industrial sources to permitting, thereby preventing a bureaucratic and economic nightmare. At the end of June, the Court struck down the tailoring rule, in part, but upheld the agency's authority to regulate carbon in other ways.

But how? Carbon dioxide is a different beast than the pollutants the act was originally designed to control. Most pollutants are troublesome in fairly small amounts; power plants that release 100 tons per year of sulfur dioxide and all other regulated pollutants need EPA permits. But many power plants emit more than 100,000 tons of carbon dioxide per year. If the 100-ton-per-year threshold were applied to carbon, small polluters like farms and schools would be subject to regulation – some 6 million facilities in all.

For sulfur dioxide, there has long been a straightforward technological way to cut emissions: burn low-sulfur coal, and "scrub" out the rest with an alkaline slurry, such as lime or ammonium sulfate. But no such fix exists for carbon. The only potential solution, to capture carbon and sequester it underground, remains technically difficult and cost-prohibitive.

So it's no small feat that states, citizens and electric utilities finally have a well-designed, achievable carbon-reduction plan to consider for power plants. The Clean Power Plan puts no direct cap on plants' carbon pollution. Rather, it sets custom targets, requiring each state to reduce the carbon intensity of its power supply by cutting the "emissions rate" – the emissions from that state's entire fleet of plants divided by the electricity they collectively generate.

States have a lot of flexibility to reach their targets. They can cut coal-fired power and increase the amount they get from natural gas and renewables. They can increase efficiency at power plants and among consumers by providing incentives for people to insulate homes and businesses, or setting new building efficiency codes. They can join regional carbon markets, like California's.

So can the Clean Air Act do for climate change what it did for acid rain? Not with the Clean Power Plan alone. The proposed cuts are fairly moderate; the decline of coal – fueled by the natural gas boom as well as state energy policies – has pushed carbon emissions down about 15 percent since 2005. In other words, we're already almost halfway to our 2030 goal.

But even if the Clean Power Plan won't end the climate crisis, it's a lot better than what existing federal policy requires, which is nothing at all. In a political atmosphere where the reality of climate change still remains mysteriously open to debate, official acknowledgement that something needs to be done may be the first step in turning things around.

• Climate Change
• U.S. Environmental Protection Agency
• Politics
• Energy & Industry
• Pollution