abbreviation for Green House Gases; "greenhouse effect" refers to the temperature regulation effect that certain atmospheric gases have on the earth. Temperature-regulating gases, called "greenhouse gases" or GHGs, form a blanket around the earth that traps heat from the sun within the earth's atmosphere, keeping the planet warm and habitable. "Global warming," or climate change, can occur when the blanket of GHGs gets thicker. Climate models from the Intergovernmental Panel on Climate Change, as well as models from other scientific bodies, indicate that global concentrations of GHGs have been rising steadily over the past 100 years. As atmospheric concentrations of GHGs increase, the greenhouse blanket gets thicker. This causes heat to be trapped in the lower layers of the atmosphere and may cause global average temperatures to rise (source: CCX FAQs).