A former U.S. Senator and presidential candidate urged green advocates in Raleigh today to press ahead with alternative energy development because the days of conventional fossil fuels are numbered.

Bob Graham, a former Florida Governor and U.S. Senator, is the former co-chair of the federal commission that studied last year's BP Deepwater Horizon oil spill, which Graham characterized as the largest man-made environmental disaster in U.S. history.

He spoke at the eight annual Sustainable Energy Conference, an event organized by North Carolina's State Energy Office.

"There was an attitude that it can't happen here, so why worry," Graham said, summarizing the commission's 500-page report. "This was an avoidable incident. It was not an act of God or nature. It was an act of mismanagement."