Greenhouse gases
From dKosopedia
The principal greenhouse gas is carbon dioxide (CO2), but others include methane, and oxides of sulfur and nitrogen. Human activity, such as the use of fossil fuels for energy production, has emitted substantial quantities of greenhouse gases into the earth's atmosphere to the point that CO2 levels in the atmosphere are measurably increasing to a degree unprecedented in Earth's history. These gases absorb infrared radiation, increasing the extent to which reflected sunlight is absorbed by the earth's atmosphere (i.e., trapping heat that would otherwise be radiated into space). This results in the greenhouse effect and global warming.