WASHINGTON (AP) -- President Barack Obama signaled his willingness to tackle climate change with his pick of Gina McCarthy to lead the Environmental Protection Agency, one of three major appointments he announced Monday.A 25-year veteran of environmental policy and politics, McCarthy has worked for Republicans and Democrats, including Obama's presidential rival, Mitt Romney, who tapped her to help draft state plans for curbing the pollution linked to global warming. Along with McCarthy, Obama nominated MIT nuclear physicist Ernie Moniz to lead the Energy Department and Wal-Mart's Sylvia Mathews Burwell to head the budget office.McCarthy, 58, a Boston native, has led the EPA's air pollution division since 2009, ushering in a host of new rules targeting air pollution from power plants, automobiles, and oil and gas production.In nominating McCarthy as the nation's top environmental official, Obama is promoting a climate change champion at a time when he has renewed his commitment to address global warming and the agency is contemplating a host of new rules that could help achieve that. But McCarthy will have to balance the administration's ambitions with a dwindling budget: Congress has cut EPA's budget by 18 percent over the last two years, and the automatic budget cuts that went into effect Friday will hinder the agency's energy efficiency programs and climate research.Moniz, as head of MIT's Energy Initiative, has worked on developing ways to produce power while curbing greenhouse gas emissions.\They're going to be making sure we're investing in American energy