These regulations are more likely to be the crux of the government's environmental work than any broad legislative proposals, said Daniel Weiss, a senior fellow for energy and environment at the Center for American Progress.
"When asked about global warming, the president has said we have to work on the economy first," Weiss said. "That reflects this idea that they'll use non-legislative tools and focus on existing authority through the EPA. They've got a lot of unfinished business."
Many of the green groups would like the agency to be more aggressive now that it has been freed from election-year pressures.
That worries Nicolas Loris, an energy economist with the Heritage Foundation, a conservative think tank that has railed against the EPA rules.
"The incentives to cater to the economy and industry are gone," Loris said. "That could mean stronger regulations … that are economically damaging. Some of the ones they've proposed are already the most stringent and unprecedented."
Last week the Natural Resources Defense Council issued a plan for EPA to use the Clean Air Act to impose tougher greenhouse gas emission standards on existing polluters that it said could cut carbon pollution by 26 percent by 2020. In a news release, NRDC executive director Peter Lehner said the plan—which would set state-specific regulations rather than a national target—shows "how the United States can make big reductions in carbon pollution that drive climate change."
With the agency's path largely set, most agree that Jackson's replacement would likely come from within the agency, so the agency can continue its work with minimal disruption.
One of the most commonly mentioned names was Bob Perciasepe, the EPA's current deputy administrator. As Jackson's second-in-command, Perciasepe was deeply involved in the agency's work during Obama's first term, including representing the agency several times in Congressional hearings. He also headed up the EPA's water and air quality departments under President Clinton and previously served as chief operating officer for the Audubon Society.
Also mentioned was Gina McCarthy, assistant administrator for the Office of Air and Radiation, who led the drafting of the EPA's air quality regulations, including the greenhouse gas and fuel economy rules.
"They've been focused on trying to make efforts to reduce the threat of pollution during a severe economic downturn," Weiss said. "That's going to continue."
A more ambitious choice would be Mary Nichols, head of the California Air Resources Board. Nichols has managed the buildup to California's cap-and-trade program for greenhouse gas emissions and has been praised for making the Golden State a worldwide leader in environmental work.
But Nichols could face fierce opposition from the business community that sees cap and trade as an economic impediment. And some supporters say she might not even be interested in the job.
"To the extent that she wants to be in a position of global leadership on climate change, California has that right now," said Roy of the Center for Climate and Energy Solutions. "EPA isn't working to the extent that California is right now and it's hard for me to see her leaving without a greater mandate."
What's at Stake for the DOE
The Department of Energy, buoyed by $90 billion in economic stimulus money set aside for clean energy programs, expanded its scope in Obama's first term beyond its traditional research and development role.
But its work in clean energy financing also opened the department to accusations of cronyism from the right, topped by the Solyndra scandal. Republicans launched several Congressional investigations into the loans, had Chu testify before the House Oversight Committee and put the loan programs on the chopping block in House budgets.
Most agree that the new DOE secretary will need to have more political chops than Chu, a Nobel Prize-winning scientist, in order to withstand Congressional investigations and negotiate with lawmakers to preserve funding for its clean energy investments. The green groups say the new secretary will have vast power to shape how the administration promotes clean energy.
"A lot of what happens at DOE depends on who the secretary is going to be," said CAP's Weiss.
Topping most lists is former North Dakota Sen. Byron Dorgan, a Democrat who served on the Energy and Natural Resources Committee and chaired the budget subcommittee overseeing the Energy Department. In the Senate, Dorgan had a reputation for working across the aisle and was a champion of clean energy, although he also supported measures that would help his home state's oil and natural gas drilling industries.