EPA

THE power plant that heats Congress produces more carbon dioxide than any other facility in Washington, DC. It is almost 100 years old and runs partly on coal, a grubby fuel. Last week, protesters marched on it, urging Congress to cut its own emissions of greenhouse gases and to oblige the rest of America to do so as well.

The first demand was easily met: the leaders of the House of Representatives and the Senate instructed their staff to convert the plant to run on natural gas, which burns more cleanly than coal. But the second one is proving trickier. Congress is just beginning to grapple with laws to regulate greenhouse gases (see article), at the behest not just of protesters but also of Barack Obama, who has long advocated vigorous measures to curb global warming. Bringing about a wholesale change in America's energy supply will be a challenge, to say the least. And the sort of measures that are currently finding favour in Washington will make it harder still.

The president is right to want to cut emissions. The alternative, allowing climate change to take its course, would be far more damaging to America and the world. The economic impact of rising sea levels, reduced crop yields, fiercer storms and many other doleful consequences would be devastating.

But fighting climate change will be costly. It will involve swapping cheap but dirty fuels for cleaner but dearer ones, as Congress intends, as well as building lots of expensive new power plants to replace older, more polluting ones. That in turn will lead to higher electricity and fuel prices. Despite the president's airy talk of green jobs, cutting emissions, by almost all calculations, will increase costs for most businesses and families. Those extra costs must be kept to a minimum.

Mr Obama's preferred device for cutting emissions, a cap-and-trade scheme, is designed to do just that. It involves placing a limit on the volume of emissions that can be produced around the country each year, and then auctioning tradable permits to pollute. The intention is to encourage firms that find it cheap to cut emissions to do so, while allowing those with no easy means to pollute less to buy permits instead. Politicians and bureaucrats, meanwhile, do not need to identify where emissions cuts should be made; the market takes care of that for them.

Sunshine and moonshine

Many congressmen are unconvinced. There is a general worry that the required emissions cuts will be harder than expected to find, pushing up the cost of the permits and thus flattening an already slouching economy. And there are particular fears that, even if the system works well enough overall, states that rely heavily on coal, heavy industry or some other sooty activity will suffer badly.

Both the president and cap-and-trade's supporters in Congress seem inclined to respond with subsidies for pet technologies that might help those hardest hit, or with mandates to cut emissions in particular ways. The president, for example, wants to double the amount of electricity that comes from renewables, meaning wind farms, solar-power plants and the like. Handouts for hybrid cars and for coal plants with low emissions are also popular.

The main effect of these schemes would be to raise the costs of cutting emissions. Much of the money doled out by the government would inevitably be wasted, adding to the overall bill for fighting climate change. Worse, such measures would risk distorting the carbon market, steering private capital as well as public money away from the cheapest technologies and towards those that have caught the eye of the politicians.

Under the stimulus bill, renewables benefit from a tax credit, grants, loan guarantees and an expensive overhaul of the electric grid. No wonder that each tonne of emissions avoided thanks to the measures in the stimulus to encourage renewable energy would cost somewhere between $69 and $137, according to a recent study. Under a cap-and-trade scheme, the price would be less than $15 to begin with, by most accounts.

There are some green things on which the government could usefully spend money. Investments in energy efficiency—of which the stimulus package included a lot—are particularly worthwhile. Increasing the budget for advanced scientific research may yield technological breakthroughs. But on the whole, government intervention is only likely to raise the cost of mitigating climate change. Fat handouts may make the politics of going green easier in the short run, but in the long run they will make it harder.