Sample Overhead


	Life on earth depends on the cycling of carbon and energy. Plants take carbon dioxide from the atmosphere, lakes, and oceans to manufacture their food using water and energy from light. Plants - and animals - use that carbon carrying food as an energy source. Humans have learned how to recover fossil fuels. We are recycling them by burning them in power plants, planes, trains, and automobiles to release carbon dioxide and water vapor to the atmosphere. Their carbon content is thus returned to the cycle of life. The whole complex process is driven by flows of energy.
	This figure from the United Nations Intergovernmental Panel on Climate Change (IPCC) provides a quantitative overview of the carbon cycle.
	The greenhouse gas “problem” is boldly stated here in the red boxes and circles as driven by fossil fuels. 3.3 billion tonnes of carbon are added to the atmosphere annually.
	Note that the atmosphere contains some 700 billion tonnes of carbon. Living plants store about 500 billion tonnes. The fossil fuel total 3300 billion tonnes. Soils hold about 2000 billion tonnes and oceans some 40,000 billion tonnes. Some 100 million billion tonnes is incorporated in sedimentary rocks. These stores are all products of earth’s life.
	We need to look at the cycle in some more detail to see if there might be clues to useful action.