Thomas Steyer, the billionaire philanthropist and champion of renewable energy, will speak at this year's American Renewable Energy Day (AREDAY) conference in Aspen, taking place August 17 through 21. Steyer helped to defeat California Proposition 23 last year, a ballot initiative funded by corporate interests to suspend the state's groundbreaking 2006 global-warming law, which aims to reduce the state's emissions of greenhouse gases down to 1990 levels by 2020.

"It's all about public health and clean air," Steyer said. "It's all about creating new jobs, and really what we're fighting is self-interested, dirty energy companies."