The difference between the greenhouse effect and global warming is that global warming is the greenhouse effect applied to the entire atmosphere and the greenhouse effect basically means how gases in an atmosphere affect the way that a closed system retains heat. Carbon dioxide plays a significant role in the greenhouse effect and global warming in a sense that plants need CO2 to survive. Also a great amount of CO2 is absorbed through natural processes. For example, the ocean absorbs C02 as well as plants. A source of greenhouse gas is a process or activity through which the gas is released into the atmosphere. Both natural processes and human activities release greenhouse gases. Carbon dioxide is released into the atmosphere when plants decay. Microorganisms that consume and break down dead plant material release carbon dioxide into the air as part of the process of breathing, just as we do. Plant decay is one of the largest sources of atmospheric carbon dioxide. Burning fossil fuels is a source of greenhouse gases. When the chemical energy in hydrocarbon-rich fossil fuel is converted into heat to drive an engine, a byproduct of this energy conversion is carbon dioxide. The cause of the seasonal fluctuation in atmospheric carbon dioxide levels is that Each spring, when the Northern Hemisphere's vegetation awakens from the dormancy of winter and begins to grow again, it removes enough carbon dioxide from the atmosphere to reduce the air's CO2 content by several parts per million. Then, in the fall, when much of this vegetation dies and decays, it releases huge quantities of carbon dioxide back to the atmosphere, raising the air's CO2 content by a small amount. In the last fifty years, the amount of carbon dioxide that has been released into the atmosphere has increased by 30% or more. This increase of C02 in the atmosphere is due to the increase of the burning of fossil fuels and increased industry over the last fifty years throughout the world.