WASHINGTON — President Obama signed an executive order on Thursday to set new goals for reducing the greenhouse gas emissions of federal agencies, his latest use of his executive authority to address the root causes of climate change and press private companies and foreign governments to follow suit. Mr. Obama’s directive orders federal agencies over the next decade to cut their emissions by an average of 40 percent compared with their levels when he won office in 2008, and to increase their use of electricity from renewable sources by 30 percent. The goals are in line with a commitment that...