As governor of Massachusetts, Mitt Romney championed what he called a "no regrets" policy on climate change. He came into office vowing to eliminate the state's SUV fleet and to close its dirtiest power plant. In 2004, his administration outlined a sweeping long-term vision for cutting the state's emissions, improving efficiency, and promoting sustainable development that was considered among the most aggressive in the country.

That was then. As with his positions on other hot-button issues, Romney's stance on global warming shifted after he started making plans to enter the 2008 presidential race. He went from stating that global warming is real and "human activity is a contributing factor" to declaring "we don't know what's causing climate change." So what does the presumptive GOP nominee really believe? And how would he address climate change if elected president? One person who may well know is Gina McCarthy, who Romney tapped for top environmental posts in Massachusetts. But these days she's not talking—presumably because she's working for President Barack Obama as a top-ranking political appointee at the Environmental Protection Agency.