WASHINGTON (AP) — Heather Zichal admits her job is unfinished.

The architect of President Barack Obama's climate-change plan, Zichal left the White House last week after five years as a top adviser on energy and climate change.

Her departure comes as the Environmental Protection Agency moves ahead with the linchpin of the president's climate plan: emissions limits for new and existing power plants to curb greenhouse gases blamed for global warming.

"Do I walk out thinking that it would have been fun to do the rule for existing coal (-fired power) plants? The short answer is yes," Zichal said in an interview.

Zichal, 37, said she has not decided on her next job but said it will involve clean energy, a field she has spent the past five years promoting as the administration moves to boost renewable energy such as wind and solar power. Obama also has increased fuel-efficiency standards and moved to tighten limits on mercury and other toxic pollution from power plants. Zichal's deputy, Dan Utech, replaced her.

Sen. John Barrasso, R-Wyo., said Zichal's departure will have little effect on the Obama administration's energy policies — or its tactics to advance them. Barrasso and other Republicans have complained that the White House has been trying to avoid congressional scrutiny of its climate-change agenda by seeking to impose policies through executive order rather than legislation.

"Personnel changes don't change the fact that this White House is clearly committed to continuing to wage a war on coal over the next three years," Barrasso said.

In a statement, Obama called Zichal a trusted adviser and "a strong and steady voice for policies that reduce America's dependence on foreign oil, protect public health and our environment, and combat the threat of global climate change."

By necessity, Zichal worked more on administrative solutions than congressional legislation after Republicans took control of the House in 2011. Obama's climate plan would be put in place through executive order, bypassing Congress, which has stalemated over climate legislation in recent years.

The administration faces a challenge as it tries to manage a huge boom in domestic oil and natural gas production while meeting its climate goals.

"You have to balance that opportunity" for increased energy with a strong regulatory framework, she said. "I think the fact that the U.S. is the world's largest producer of natural gas tells you a lot about where the market is going and what's at stake."