Becoming a grandfather is cause for celebration, unless you’re a coal-fired power plant.

Coal plants that predate the Clean Air Act have become the mules of air pollution—set in their ways and not liable to change. Exploiting their "grandfathered" status, these coal plants have refused to implement technologies that are currently available to reduce pollution.

Now, Congress seems determined to let these dinosaurs off the hook all over again.

Although the Environmental Protection Agency’s recent Clean Air Act endangerment finding prescribes a strong antidote to global warming pollution—a fact President Obama will surely highlight tomorrow on the final day of climate negotiations in Copenhagen—a political compromise over coal plants threatens to bind EPA’s hands just as it begins to act.

The endangerment finding, based on overwhelming scientific evidence, says that global warming pollutants like carbon dioxide threaten human health and welfare. As a result, the Clean Air Act requires EPA to reduce global warming pollution from a wide range of sources, including cars, factories, and perhaps most importantly, coal-fired power plants.

Coal-fired power plants account for more than a third of U.S. global warming pollution, and as MIT researchers recently concluded, any credible solution to global warming must address emissions from these existing facilities. Period. The Clean Air Act is a powerful tool to do so, and it has in the past successfully reduced harmful pollutants.

But some legislators, feeling the heat from industry (not the planet), struck a deal as part of the American Clean Energy and Security Act—a cap-and-trade bill narrowly passed in June 2009 by the House of Representatives—that restricts EPA’s regulatory power under the existing Clean Air Act. If adopted in a final law, the deal would make grandfathers of the 600-plus existing coal plants in the United States, allowing them to take a pass on new technology that would reduce global warming pollution.

It’s imperative that this doesn’t happen, and we’re working hard to ensure a Senate bill leaves the Clean Air Act intact. To those tempted to believe that new authorities Congress is considering in global warming legislation are in some way incompatible with tools currently provided by the Clean Air Act, nothing could be further from the truth.

A cap on global warming pollution and the Clean Air Act work in complementary fashion. The cap sets an economy-wide limit on global warming pollution that decreases over time. Meanwhile, we need to constantly improve fuel efficiency standards for cars and use the Clean Air Act to zero in on other large sources of pollution like coal-fired power plants to ensure they also rapidly reduce emissions.

In other words: The cap is the floodlight. The Clean Air Act is the laser pointer.

Without the Clean Air Act emissions standards, a cap has too much risk of leaking. Dirty coal plants will continue to operate and pollute unchallenged for 15 years or more, stifling the growth of a clean energy economy and jeopardizing the possibility of achieving mid-term and long-term targets for reducing pollution.

And let’s not forget that we made this mistake in the past, with troubling consequences. Before the Clean Air Act passed in 1970, legislators struck a deal with industry in which existing coal plants were "grandfathered" under the new law, meaning the facilities were not required to adopt modern controls to cut down on air pollution. The logic was that the antiquated plants—called "clunkers" by some—would soon close their doors and cap their smokestacks for good.

But logic failed. The loophole actually encouraged coal plant operators to extend the life of old, dirty plants, many of which are still operating today.

We don’t have time to make this mistake again, and we shouldn’t give coal plants a perverse incentive to continue polluting at the expense of clean energy, our health and the planet. It’s time to move towards a clean energy future, and like it or not, coal-fired grandfathers just aren’t a part of it.