News outlets are reporting that Lisa Jackson, head of the Environmental Protection Agency, will not return for the second term of the Obama administration.
Jackson will probably be remembered as the point person for the first US attempts to regulate greenhouse gas emissions. It wasn't necessarily a position that she—or Obama—chose. But partisan gridlock ensured that there would be no legislation addressing emissions, and Jackson inherited a Supreme Court decision from the Bush administration that indicated the Clean Air Act required some sort of action. Within months of the inauguration, Jackson's EPA used Bush-era research to issue an endangerment finding on greenhouse gasses. Three years later, that finding led to the first limits imposed on carbon dioxide emissions by large sources, limits that would severely curtail the construction of new coal plants.
By the time they were issued, however, a sharp fall in the price of natural gas was already doing more to limit the use of coal than any EPA regulation could. (Fracking, which led to the plunge in prices, was also the subject of some initial EPA oversight.)
Under Jackson's leadership, the EPA also negotiated with automakers to finalize a deal that was first cut as part of the auto bailout package. That agreement will cut carbon emissions by increasing the average fuel economy of cars sold in the US, and it marked the first time that such standards were raised in 20 years.
Whoever replaces Jackson will likely face a very different set of challenges. Most of the big decisions appear to have been made, but the lawsuits that will attempt to keep them from taking effect are probably just getting started.