The earth is surrounded with a layer of gases, and energy from the sun enters the earth’s atmosphere by passing through this layer. The earth land and water absorb much of this energy but some is reflected back away from the earth. The rest of the energy remains close to the earth.
Since the industrial revolution, the concentration of these gases including carbon dioxide has increased through out use of fossil fuels and these are becoming trapped in this layer of gas.
This has caused an increase in temperature and scientists agree the average temperature increase must be kept to no more than 20C to avoid the most dramatic and far reaching impacts. This process is generally known as climate change.