Carbon dioxide (CO2) is the most important of many human-generated “greenhouse gases”—gases that are contributing to a gradual warming of the planet. These gases, many of which have always existed in the atmosphere, contribute to a balance of heat flows that has given us a relatively stable climate. Since the beginning of the Industrial Revolution, however, the concentration of CO2 in the atmosphere has grown from its historical average of 280 parts per million (ppm) to over 380 ppm and counting.