One carbon footprint at a time, people are hoping to change the world. In their zeal to save the planet, folks appear willing to support a variety of market-distorting measures to shift power generation away from fossil fuels and toward renewable energy.

That's translating into action. Regulatory wheels have been set in motion to affect that shift, and there are quite a few interesting investment opportunities as a result.

While the nuclear, wind, and solar industries are great for investing on a macro level, proactively reducing emissions trickles down to consumers and their vehicles. In transportation, we should see some regulatory incentives for companies that adhere to global emissions standards defined by the Environmental Protection Agency (EPA) and the Kyoto Protocol.

Let's look at a few of the key players moving the automotive industry toward greener pastures.

The auto parts suppliers
Magna International (NYSE:MGA) produces such a wide array of auto parts, there's no room to list them here. It sells its wares to General Motors (NYSE:GM), Ford (NYSE:F), Daimler, Volkswagen, and BMW, among others. Last month, Magna's electronics unit acquired BluWav Systems, a developer and supplier of energy-management systems for electric and hybrid vehicles. Magna now trades at less than half of its tangible book value per share, giving it a substantial margin of safety in liquidation even if its book values are somewhat inflated. Magna would be a no-brainer buy under normal conditions -- but of course, these aren't normal conditions.

Both drivetrains and transmissions are major areas for improvement for automobile emissions, and BorgWarner (NYSE:BWA) supplies its state-of-the-art products to the big three U.S. automakers as well as a variety of European and Asian customers. Its components are used in advanced gasoline engines that significantly reduce carbon dioxide emissions relative to conventional engines. Its drivetrain systems are designed with fuel economy in mind, and its management recently upped its quarterly dividend by 9% to $0.12 per share.

More negatively impacted by the economic crisis than its cousins mentioned above, Tenneco (NYSE:TEN) has developed diesel particulate filters, along with other advanced control solutions that provide its customers with state-of-the-art emissions reduction technology. Clean diesel engines deliver 20% to 30% better fuel economy than gasoline power, and Tenneco is looking to capitalize on its strong technological position in emission control to capture a top share of the forthcoming growth opportunities.

Now, should the big three U.S. automakers take a turn for the worse, there's no guarantee -- at least, not in the short run -- that the parts suppliers would be capable of offsetting the losses. If you don't think Detroit will go the way of the dinosaur, then these companies look pretty attractive. However, if your prognosis is that GM, Ford, and Chrysler are doomed, then there are other opportunities you can consider.

A pair of automakers
Honda Motor (NYSE:HMC) has had some success selling its diesel engines in Europe, and it plans to expand its diesel vehicle production into that region to meet the growing demand. Its eighth-generation Accord is being mass-produced in three types, all of which meet the 2009 Euro 5 emissions standards. Honda has also announced its voluntary global carbon dioxide reduction targets for both its products and production activities for 2010, so it is already well-positioned to take advantage of any incentives offered for adherence to environmental standards.

In addition, Toyota Motor (NYSE:TM) has recognized that in order for it to achieve sustainable mobility, it must dedicate itself to reducing CO2 emissions, supporting alternative energy sources, and improving air quality. It believes that hybrid technologies, with their ability to be combined with diesel and fuel cells, will be the core of all future powertrains. It aims to sell a million hybrid vehicles annually by the early 2010s if possible, and it has a peripheral goal to have its hybrid technologies integrated into all of its vehicle models by the late 2020s.

Vehicular emissions can be reduced in a number of ways, but these five companies deserve a closer look for their approaches to cleaner energy -- especially because their stock prices have mostly taken a beating this year. Those losses shouldn't surprise anyone who has been following the saga of Detroit's Big Three; nonetheless, if you think we've seen the worst of the economic apocalypse, they may well be temporary.

Of course, these five stock ideas are only the tip of the iceberg for climate-change investing; they're not recommendations per se, just ideas to jump-start your research. Toward that end, check out these related Fool articles:

Fool contributor Chris Jones does not own shares in any of the companies mentioned. BorgWarner and BMW are Motley Fool Stock Advisor recommendations. The Motley Fool's disclosure policy produces less "Well-to-Wheel" carbon emissions than any alternative or conventional engine under production.