Robert Redford, shown here at an event for the movie "Lincoln." argues in a new ad that Obama could do more to address climate change. (Credit: www.washingtonpost.com) Robert Redford, shown here at an event for the movie "Lincoln." argues in a new ad that Obama could do more to address climate change. (Alex Brandon/AP)

A major national environmental group has enlisted legendary movie star Robert Redford in its effort to pressure President Obama to move quickly to curb greenhouse gas emissions from power plants.

The Natural Resources Defense Council will air ads on television, online and in social media outlets in which Redford, an NRDC trustee and longtime environmental activist, urges Obama to have "the courage of his convictions."