There is a rule for judging solutions to the twin problems of energy dependence and global warming: A policy designed to solve one problem should not make the other worse. But that is a likely outcome of the many “energy independence” bills circulating in Congress that aim to build a whole new generation of coal-to-liquid plants to convert coal into automotive fuel.

These bills have already acquired an enthusiastic constituency and will be offered as amendments to what is now a relatively simple and sound energy bill designed to increase the fuel efficiency of cars and light trucks, encourage the production of biofuels and provide research and development money for the capture and storage of carbon dioxide emissions from power plants.

There are, of course, ways to make this bill better. Senator Jeff Bingaman will offer a useful amendment to require utilities to generate a percentage of their electricity from renewable sources like wind. But there are also ways to make the bill a lot worse. One of them is to require the expenditure of billions of dollars in loans, tax incentives and price guarantees to lock in a technology that could end up doing more harm than good.

Coal is far and away America’s most abundant fuel. It provides more than half the country’s electricity. And there is no doubt that it could substitute for foreign oil, although how much and at what price is not clear. In addition, the technology to convert coal into liquid fuels is well established. But it is also true that between the production process and burning it in cars, coal-to-liquid fuel produces more than twice the greenhouse gas emissions as gasoline and nearly twice the emissions of ordinary diesel. These are terrible ratios.