If the rule survives the inevitable legal challenges, it will mark the first time the federal government limits air pollution from carbon dioxide.
Even states that sued Obama over the EPA's new rules to combat climate change are trying to figure out how to comply with them.
Even before Obama released his rules to reduce greenhouse gas emissions, dozens of cities pledged to become carbon-free. But how they will achieve that isn't always known.
Historic snowstorms brought the city's buses and trains to a standstill for weeks. Is new leadership enough to get the agency back on track?