Greenhouse gases are already outside of the atmosphere, but they contribute to the greenhouse effect. These gases occur naturally in the atmosphere and there are others that occur due to human activity. The natural gas found in the atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. There are so very high levels of greenhouse gases caused by human activity. The main sources of greenhouse gases from human activities have contributed are the burning of fossil fuels, the use of chlorofluocarbons found in refrigeration systems.
Also the share of agricultural activities such as playing the use of fertilizers, which can cause a high amount of nitrous oxide.