It is not always obvious which companies will profit from the push to combat climate change and promote the use of alternative fuels. Makers of wind turbines and biofuels will surely benefit — but so will makers of railcars and auto-emissions controls.

Here are five ways to invest in a cleaner world:

• General Electric (symbol GE; recent price $41). The giant conglomerate is a major producer of wind turbines and clean-coal technology, not to mention energy-efficient locomotives, jet engines, home appliances and light bulbs.

It estimates that revenues from its clean-energy businesses were $12 billion last year (out of $163 billion total) and predicts that the figure will rise to $20 billion by 2010. And that doesn't include $1 billion in annual revenues from GE's nuclear-energy business.

• Honda Motor (HMC; $33). Any serious attempt to reduce greenhouse gases will need to zero in on the auto industry. That's why we like Honda Motor, whose fleet of cars, including the Accord, Civic, Odyssey and Acura names, is the most fuel-efficient of any major carmaker.

That means the Japanese firm will benefit from tighter U.S. fuel-economy standards. The Civic Hybrid, for example, gets up to 45 miles per gallon.

• McDermott International (MDR; $55). The U.S. leans on its plentiful but dirty coal reserves for half of its electricity generation. The solution then is to clean up the coal. McDermott International's Babcock & Wilcox division has cutting-edge technology for scrubbers that capture harmful coal emissions before they are released into the atmosphere.

So McDermott stands to gain as environmental regulations mandate retrofits and upgrades to existing coal-fired plants. The Houston-based engineering-and-construction company is also a leading supplier to the nuclear industry.

• Ormat Technologies (ORA; $45). Geothermal power is a renewable energy technology that is not dependent on weather. The technology uses hot water and steam from deep underground to turn turbines and generate electricity. Ormat Technologies is the third-largest geothermal firm in the U.S. and the only one of the top three that focuses exclusively on geothermal power.

Its shares are pricey, but the Reno, Nev., company stands to benefit from government mandates in California and Nevada (where most of its U.S. plants are located) that require utilities to buy more power from renewable sources.

• United Technologies (UTX; $79). This splendidly run industrial conglomerate focuses on energy conservation both within the company and with the products it sells. Its Otis elevator and Carrier heating and air-conditioning units are developing more energy-efficient systems. The company also makes fuel cells for buildings, transit buses and the U.S. space program.

David Landis is a contributing editor and Andrew Tanzer is a senior associate editor at Kiplinger's Personal Finance magazine. Send your questions and comments to [email protected]