The carbon cycle is a complex series of processes through which carbon atoms rotate between the living world, the atmosphere, oceans and the Earth's crust. In the carbon cycle there are various sinks, or stores, of carbon and processes by which the various sinks exchange carbon.
Each year, more than 120 billion tonnes of carbon is exchanged between all living things during photosynthesis and respiration. Plants absorb about 61 billion tonnes of carbon and respire about 60 billion tonnes.
The burning of fossil fuels by humans adds about 6.5 billion tonnes of carbon each year in the form of carbon dioxide. Land clearing, reduced soil humus and the erosion of topsoil account for 1 to 2 billion tonnes of carbon a year.
 | The amount of carbon dioxide that people add to the atmosphere may seem very small in comparison to the amounts being added and absorbed by natural processes, but it only takes a small change to upset the equilibrium. Human activities have added extra carbon to the atmosphere, putting the carbon cycle out of balance. This is expected to result in continuing increases in atmospheric carbon dioxide concentrations. The performance of the carbon cycle is linked to the temperature of the Earth. Scientists are working to understand how the carbon cycle operates and adjusts |
to the changing amount of carbon dioxide in the atmosphere. Greenhouse gases are a natural part of the atmosphere. They trap the sun's warmth, and maintain the Earth's surface temperature at a level necessary to support life. The problem we now face is that human actions-particularly burning fossil fuels (coal, oil and natural gas) to produce our energy and land clearing-are increasing the concentrations of these gases that trap more heat and change the climate. This is the enhanced greenhouse effect. |  |
The carbon cycle is a complex series of processes through which carbon atoms rotate between the living world, the atmosphere, oceans and the Earth's crust. In the carbon cycle there are various sinks, or stores, of carbon and processes by which the various sinks exchange carbon.
Each year, more than 120 billion tonnes of carbon is exchanged between all living things during photosynthesis and respiration. Plants absorb about 61 billion tonnes of carbon and respire about 60 billion tonnes.
The burning of fossil fuels by humans adds about 6.5 billion tonnes of carbon each year in the form of carbon dioxide. Land clearing, reduced soil humus and the erosion of topsoil account for 1 to 2 billion tonnes of carbon a year.
| The amount of carbon dioxide that people add to the atmosphere may seem very small in comparison to the amounts being added and absorbed by natural processes, but it only takes a small change to upset the equilibrium. Human activities have added extra carbon to the atmosphere, putting the carbon cycle out of balance. This is expected to result in continuing increases in atmospheric carbon dioxide concentrations. The performance of the carbon cycle is linked to the temperature of the Earth. Scientists are working to understand how the carbon cycle operates and adjusts |
to the changing amount of carbon dioxide in the atmosphere. Greenhouse gases are a natural part of the atmosphere. They trap the sun's warmth, and maintain the Earth's surface temperature at a level necessary to support life. The problem we now face is that human actions-particularly burning fossil fuels (coal, oil and natural gas) to produce our energy and land clearing-are increasing the concentrations of these gases that trap more heat and change the climate. This is the enhanced greenhouse effect. | |