EACH of us took turns over the past 43 years running the Environmental Protection Agency. We served Republican presidents, but we have a message that transcends political affiliation: the United States must move now on substantive steps to curb climate change, at home and internationally. There is no longer any credible scientific debate about the basic facts: our world continues to warm, with the last decade the hottest in modern records, and the deep ocean warming faster than the earth’s atmosphere. Sea level is rising. Arctic Sea ice is melting years faster than projected. The costs of inaction are undeniable....