Age: It may not be apparent yet, but the most important and enduring legacy of President Barack Obama's two terms in the White House may prove to be the Clean Power Plan, which aims to reduce greenhouse gas emissions. The plan gives teeth to the United States' promise of compliance with globally agreed temperature targets, set two months ago at the UN climate change talks in Paris.
The plan hinges on having the US Environmental Protection Agency require states to curb coal-fired power stations' carbon-dioxide...