Is a new stock index really going to help anyone identify and track companies with low carbon emissions?

Apparently so. The companies listed in the just announced Standard & Poor U.S. Carbon Efficient Index had a carbon footprint (as defined by S&P) that was 48 percent lower than the average company on the S&P 500. S&P calculates the carbon footprint by dividing greenhouse gas emissions by annual revenue.

The list currently has 362 companies on it as and, as one might imagine, is heavily skewed toward IT companies that sell products and services that rely more heavily on intellectual property than raw materials and natural resources. The organization, however, is examining all 4,500 companies on its indexes.

"Organizations around the world are paying greater attention to the impact of greenhouse gases on our climate, as increasingly more investors consider carbon efficiency as an important investment theme," said David Blitzer, Managing Director and Chairman of the Index Committee at Standard & Poor's Index Services in a prepared statement.

Carbon emissions, of course, are more than just a feel-good measure. Carbon cap-and-trade systems are already imposing costs on European companies and either a tax or cap-and-trade system is expected to come to the states. Low carbon emissions also indicate greater energy efficiency, i.e., more revenue per less fossil fuel unit than competitors. With sales expected to be somewhat stagnant to depressed for many companies over the next year, investors will focus more on cost cutting and efficiency measures.

In the past few years, investment banks have also pulled, or threatened to pull, funding on coal burning power plants.