Thirteen of America's best-known companies -- including Apple, Google, Microsoft, Walmart and Bank of America -- have pledged $140 billion toward efforts to reduce carbon emissions. The companies on Monday helped launch the American Business Act on Climate Pledge, part of an Obama administration effort to enlist private companies in the fight to slow climate change.

President Barack Obama has set an ambitious goal of reducing U.S. greenhouse gas emissions economy-wide by up to 28 percent below 2005 levels by 2025. In addition to setting an example for its peers, the 13 businesses signing the pledge agree to support "a strong outcome" at an international climate change summit in Paris later this year. Some have set company-specific goals to cut emissions as much as 50 percent.