How does human activity create an enhanced greenhouse effect?

Greenhouse gases, such as CO2, increase trapped heat in the earths atmosphere leading to a global warming effect. Human activities can cause an increase in greenhouse gases in a number of ways.
The burning of fossil fuels for energy, transport or industry releases the greenhouse gas of CO2, enhancing the greenhouse effect. Deforestation is another activity that enhances the greenhouse effect. When trees are cut down they no longer act as carbon sinks, the process of photosynthesis is stopped and therefore there will be less CO2 taken out of the atmosphere. Furthermore some of the deforested trees will be burned in industry or for fires leading to the release of more CO2.