Anything that increases carbon dioxide (CO2) levels is a risk factor in heating up the planet. In addition to CO2, methane gas (CH4) and chlorofluorocarbons (CFCs) are culprits in global warming. Methane (from livestock, coal mining, and also natural sources like peat bogs and termites decomposing wood) is actually 25 times more effective in holding heat within our atmosphere, and CFCs are 20 thousand times more efficient than CO2.

Methane gases during the 1990s were rising at an annual rate of about 0.8 percent; from 1997 to 2007, however, methane levels stabilized, and scientists believed that a balance had been reached between production of methane gas and its rate of dissipation in the atmosphere. In 2007, however, a sudden spike in methane levels was noted, especially in the Northern Hemisphere, for reasons not well understood. Theories include the idea that global warming increased methane production from wetlands bacteria (i.e., the result of melting permafrost, especially in Siberia), or that the amount of OH (hydroxyl free radical), which breaks down methane, is decreasing in the atmosphere. Today, the amount of methane in the air is more than twice what it was before the Industrial Revolution (about 1,775 parts per billion versus about 700 parts per billion). The current rate of increase for methane is about 10 parts per billion annually, which is considered a significant spike. Meanwhile, because of government regulations, CFC levels have been steadily decreasing in the atmosphere, which is particularly good news for the ozone layer.