Reuters: Here’s what leading U.S. presidential candidates have said about climate change, and what they want to do about it. DEMOCRATIC NEW YORK SEN. HILLARY CLINTON: "We need to start on a path to slow, stop and reverse the growth of greenhouse gas emissions." Supports an 80 percent reduction in carbon emissions by 2050, 40 mile-per-gallon fuel efficiency standard by 2017 and 10 percent cut in energy consumption by 2020. FORMER DEMOCRATIC SOUTH CAROLINA SEN. JOHN EDWARDS: …