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 act like a cap, making it more difficult for Earth to get rid of the energy it absorbs from sunlight. Without these gases to absorb the energy, our planet’s average surface temperature would have been near zero degrees Fahrenheit. Of the remaining 1% of the atmosphere, the main molecules that can absorb infrared radiation are CO2 and water vapor, because their atoms are able to vibrate in just the right way to absorb the energy that the Earth gives off. The concentration of carbon dioxide in Earth’s atmosphere is currently at nearly 412 parts per million (ppm) and rising, which represents a 47 percent increase since the beginning of the Industrial Age, when the concentration was near 280 ppm.