Question

Why would increased levels of greenhouse gases contribute to higher temperatures. On earth?

Answer 1

Answer;
This is because greenhouse gases prevent heat which is received from the sun from being radiated out into space. 

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. 

Answer 2

Greenhouse gases are the gases in the atmosphere that keep the air in the atmosphere.  It traps the sun's sunlight.  Since the heat is trapped in here, it would contribute to higher temperatures.