Talk about carbon emissions all you like, but growth in this hotly debated area has been slowing. Total carbon emissions grew only 1.4% over 2011 on a global scale. One of the largest reasons carbon emissions are slowing is because of the United States. Between 2011 and 2012, total carbon emission reductions from the U.S. were three times greater than all of Europe and Eurasia combined. Today, the U.S. emits the same amount of carbon as we did in 1994, and this downward tend could continue for the next couple of years. 

More work can be done to reduce carbon emissions through better energy sources and increased efficiency, but we should give some credit to the reductions we have achieved thus far. Utilities switching from coal to natural gas reduce CO2 emissions per MW produced by about 50%, saving some money at the same time. Also, automotive manufacturers have found new ways to get more out of every drop of gasoline. In the past five years, Ford (NYSE:F) has increased its entire vehicle fleet efficiency by 14%.  

In some ways, the improvements we have made thus far are the low-hanging fruit, but there are several companies making the investments to spur the next big improvements in efficiency and carbon emission reductions. Tune in to the following video, where contributor Tyler Crowe discusses some of these forward-looking companies.

Fool contributor Tyler Crowe owns shares of Westport Innovations. You can follow him at under the handle TMFDirtyBird, on Google +, or on Twitter, @TylerCroweFool.

The Motley Fool recommends Clean Energy Fuels, Ford, Nucor, Southern, and Westport Innovations and owns shares of Ford and Westport Innovations. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.