Since the late 1950s, scientists have documented rising levels of carbon dioxide and other "greenhouse gases" in Earth's atmosphere. Laboratory tests and physics experiments indicated that these gases absorb some of the infrared radiation that Earth emits into space, thereby raising the planet's temperature. This is called the greenhouse effect because it is similar to how a glass greenhouse traps heat, warming the air inside. Put simply, more energy is flowing into the greenhouse than is getting out, a concept that scientists call radiative forcing. [Infographic: Earth's Atmosphere Top to Bottom]
The research team measured radiative forcing on the Earth's surface due to carbon dioxide at two long-running atmospheric research sites owned by the Department of Energy. One is in Oklahoma and the other is near Barrow, Alaska, above the Arctic Circle.