Investors like certainty – and if they aren’t going to get it from Washington, they’ll try to impose it themselves.

That’s one lesson from today’s announcement, first reported in the WSJ, that three big Wall Street investment banks are rolling out a new set of environmental standards to tighten their financing requirements for coal-fired power plants in the U.S.

Mohave Generating Station (Wikipedia)

Citigroup Inc., J.P. Morgan Chase & Co., and Morgan Stanley say they expect a federal greenhouse-gas-emissions cap in the next few years that will make conventional coal-fired power plants riskier investments. Given that no one knows exactly what such a cap will look like, the banks say they’ll make some conservative assumptions as they screen power-plant financing requests starting now.

We’ve talked before about how uncertainty about U.S. global-warming policy is forcing changes within industry. Now the banks are mobilizing. Under their new “Carbon Principles,” the banks will require companies applying for coal-fired power-plant financing in the U.S. to show they’ve first looked at energy-efficiency and renewable-energy options and found them insufficient. As for proposed coal-plants themselves, the banks want to see evidence either that the plants are being designed to be able to capture and store underground their carbon-dioxide emissions down the road, or that the plants will be able to charge high enough electricity rates to pay for the extra emission allowances they’d need to keep coughing out CO2 under an emissions cap.

Wall Street’s new carbon screen clearly will make it tougher to finance conventional coal-fired plants in the U.S. How hard is, well, up in the air. The banks’ bid for investment certainty rests on two big uncertainties: when the technology to capture and “sequester” power-plant CO2 emissions will be ready for prime time, and whether the power industry will have to pay for its emission allowances under a U.S. cap or will get them handed out for free.

As last week’s decision by the Department of Energy to effectively nix the FutureGen clean-coal research effort showed, it’s far from clear how to solve global warming by burying it. And though Wall Street may want to assume for the sake of conservative planning that the utility industry will have to buy all its emission allowances under a federal greenhouse-gas cap, coal-fired power producers are lobbying to be given their allowances by Uncle Sam — an arrangement that would help protect coal.