NASA's Orbiting Carbon Observatory-2, or OCO-2, is viewed for the last time in the mobile service tower at Space Launch Complex 2 on Vandenberg Air Force Base in California before the Delta II payload fairing encloses it completely for launch. The fairing will protect OCO-2 during launch aboard a United Launch Alliance Delta II rocket, scheduled for 5:56 a.m. EDT on July 1. OCO-2 is NASA’s first mission dedicated to studying atmospheric carbon dioxide, the leading human-produced greenhouse gas driving changes in Earth’s climate. OCO-2 will provide a new tool for understanding the human and natural sources of carbon dioxide emissions and the natural "sinks" that absorb carbon dioxide and help control its buildup. The observatory will measure the global geographic distribution of these sources and sinks and study their changes over time.