The fossil fuels, CO2, greenhouse effect, and climate change are all things that are connected with each other and contribute for each successive one to occur. The fossil fuels are heavily used by the humans. Through their burning, the fossil fuels release lot of CO2 into the atmosphere. The CO2 is the most common greenhouse gas, thus it is a gas that manages to trap the heat into the atmosphere. So as the CO2 from the burning of the fossil fuels increases in the atmosphere, the greenhouse effect also increases. The greenhouse effect is the one that manages to keep the Earth warm, which is good, but it can also pass the limit and make the whole planet much warmer, resulting in rise of the sea levels because of the melting of the ice caps and glaciers. That will cause significant climate changes all over the globe because the sea currents will change, the atmosphere will keep more heat, and the water surface will increase.