What is the greenhouse effect?

The natural greenhouse effect is how the atmosphere works to absorb and reflect radiation to keep the Earth warm. The sun emits short wave radiation towards the Earth. The Earth's atmosphere absorbs this heat and then radiates long wave (infrared) radiation away from Earth. Greenhouse gases (Carbon dioxide, methane, nitrous oxide) act as a barrier in the atmosphere so they re- radiate some of this heat/long wave radiation, keeping it in the atmosphere. This is what maintains our warm climate so makes life possible on Earth. HOWEVER, the excess of greenhouse gases in the atmospere due to human activity like burning fossil fuels, means that too much of the sun's radiation is being kept in the atmosphere, rather than being reflected away so global warming is occuring. This is the human induced greenhouse effect.