Answer;
This is because greenhouse gases prevent heat which is received from the sun from being radiated out into space.
Step-by-step explanation;
Green house gases are gases that are emitted into the environment that are capable of absorbing infrared radiation, and thus trapping and holding heat in the atmosphere. The increase of heat in the atmosphere contributes to higher temperatures and causes the greenhouse effect, which results to global warming. Examples of these gases include, carbon dioxide, methane, nitrous oxide, ozone and CFCs among others.