Environmental Protection Agency Administrator Lisa Jackson, the Obama administration’s chief environmental watchdog, announced December 28 that she is stepping down after  nearly four years.  Her high-profile tenure, included  lightening-rod controversies over global warming, the Clean Air Act, the Keystone XL oil pipeline, new regulations on coal-fired plants, new fuel economy standards for cars and trucks, among several other contentious issues.

Jackson, a chemical engineer, did not give any particular reason for her departure.  She was an early nominee by Obama, confirmed by the Senate on January 22, 2009, as the first African-American EPA administrator. Historically, Cabinet members that wish to move on usually do so at the start of a president’s second term.  She will leave sometime after President Barack Obama delivers his State of the Union address in late January.

If a nominee to replace her has not been confirmed by then, the White House said it plans to have Jackson’s deputy administrator and former head of the EPA’s air and water offices during the Clinton administration Robert Perciasepe, serve as the acting administrator. In addition to Perciasepe, the names being considered as potential Jackson successors include Gina McCarthy, the current top EPA air pollution official and a one-time environmental aide to then-Massachusetts Governor Mitt Romney, and former Clinton White House aide Ian Bowles, who ran the energy and environmental department in Massachusetts.   Whomever succeeds Jackson will inherit a large, unfinished agenda, including the need to issue new health protections against carbon pollution from existing power plants.

Environmental groups praised Jackson for her strong advocacy for health and the environment in tackling some thorny environmental problems. However, she sometimes clashed with the White House, constantly battled with strong opposition from Republicans on Capitol Hill, and many industry groups that said the agency’s new rules came at far too high an economic cost, destroyed American jobs, jeopardized energy security and economic recovery, and made it more difficult for American companies to compete.