Greenhouse gases are a group of compounds that are able to trap heat (longwave radiation) in the atmosphere, keeping the Earth's surface warmer than it would be if they were not present.1 These gases are the fundamental cause of the greenhouse effect.2 Increases in the amount of greenhouse gases in the atmosphere enhances the greenhouse effect which is creating global warming and consequently climate change.
Greenhouse gases allow sunlight (shortwave radiation) to pass through the atmosphere freely, where it is then partially absorbed by the surface of the Earth.3 But some of this energy bounces back out towards space as heat. Of the heat emitted back to space, some is intercepted and absorbed by greenhouse gases in the atmosphere. This is because these compounds are made of three or more atoms. This molecular structure allows them to absorb some of the escaping heat and then re-emit it towards the Earth which increases global temperatures.
The ability of these gases to trap heat is what causes the greenhouse effect. So the more greenhouse gases you have in the atmosphere, the more heat stays on Earth. This process, which is very similar to the way a greenhouse works, is why the gases that can produce this effect are collectively known as greenhouse gases.
There are 2 ways that a greenhouse gas (often abbreviated GHG) can enter our atmosphere. One of them is through human activities. The main human sources of GHG emissions are: fossil fuel use, deforestation, intensive livestock farming, use of synthetic fertilizers and industrial processes. The other is through natural processes like animal and plant respiration.