Carbon dioxide (CO2) makes up about 0.04% of the Earths atmosphere. While this may seem like a small amount, it plays a significant role in global warming. CO2 and water vapor are the main molecules that can absorb infrared radiation, which is emitted by the Earths surface as heat. These gases trap some of the heat within the atmosphere, making it more difficult for the Earth to get rid of this energy. The concentration of CO2 in the atmosphere is currently at nearly 412 parts per million (ppm) and rising, representing a 47% increase since the beginning of the Industrial Age, when the concentration was near 280 ppm. Humans have contributed about one-third of the CO2 currently in the atmosphere since 1850.