Very little water vapor ever rises above the troposphere (where the majority of Earth's weather occurs) but the little bit of vapor that makes it to the stratosphere is kind of a big deal. One recent study suggests that just a one to two percent increase in mid-stratospheric humidity can retain up to twice as much CO2—the equivalent of a decade's worth of greenhouse gas emissions. However, these estimates are based on severely incomplete climate models. An ambitious NASA program hopes to patch these data gaps with the help of America's biggest UAV.
That UAV of course is the Northrop Grumman RQ-4 Global Hawk, of which NASA scored two from the US Air Force back in 2007. Each $108 million unmanned aircraft measure 44 feet long and 15 feet tall with a 116 foot wingspan. A single Allison Rolls-Royce AE3007H turbofan engine generates 7,050 pound-foot of thrust to speed the 22,000-pound UAV to speeds approaching 500 MPH.