Environmental Protection Agency head Lisa Jackson has announced her resignation ahead of President Obama’s second term. Jackson departs after a four-year tenure that saw advances in the regulation of environmentally harmful practices such as mountaintop removal and the emissions of harmful chemicals from industrial plants. But it was also marked by a number of key disappointments on environmental issues owing to Republican opposition and a lack of White House support. President Obama rejected Jackson’s proposal for tougher regulations on smog pollution last year, even though Jackson submitted a proposal she viewed as a major compromise. She has recently tried to impose restrictions on carbon emissions from new power plants, drawing a concerted Republican and corporate pushback. After ignoring global warming during the 2012 campaign, Obama has recently vowed to address it during his second term. In a statement, the Natural Resources Defense Council called Jackson an unrivaled “champion of our health and our environment,” adding: “Her successor will inherit an unfinished agenda that begins with the issuance of new health protections against carbon pollution from existing power plants — the largest remaining driver of climate change that needs to be controlled.”