CARBON CYCLE

Human Impact

Like all other animals, humans participate in the natural carbon cycle, but there are also important differences. By burning coal, oil, and natural gas, humans are adding carbon dioxide (CO₂) to the atmosphere much faster than the carbon in rocks is released through natural processes. And clearing and burning forests to create agricultural land converts organic carbon to carbon dioxide gas. The oceans and land plants are absorbing a portion, but not nearly all of the CO₂ added to the atmosphere by human activities.

HUMAN IMPACT ON THE CARBON CYCLE
The red arrow, representing rapid fossil fuel burning, indicates the main way in which humans affect the natural carbon cycle. Carbon dioxide (CO2) levels are increasing because the natural system cannot keep pace with this new emission source. The natural processes that permanently remove this additional carbon - ocean uptake and sedimentation - work extremely slowly.	OCEAN UPTAKE - Dissolving of CO2 gas into the oceans and inflow of carbon carried from land by rivers. OCEAN RELEASE - Return of carbon in the oceans directly back to the atmosphere as CO2 gas. SEDIMENTATION - Slow burial of plant and animal matter on land and on the ocean floor, which eventually becomes limestone, coal, gas, and oil. RESPIRATION - Slow combustion of carbon compounds, producing energy within organisms and releasing CO2. PHOTOSYNTHESIS - Conversion of CO2 into energy-rich carbon compounds by plants.

Human Impact On The Carbon Cycle

The red arrow, representing rapid fossil fuel burning, indicates the main way in which humans affect the natural carbon cycle. Carbon dioxide (CO₂) levels are increasing because the natural system cannot keep pace with this new emission source. The natural processes that permanently remove this additional carbon – ocean uptake and sedimentation – work extremely slowly.

Time

Natural changes to the carbon cycle have been very slow compared to the rate at which humans are adding CO₂ to the atmosphere. The redistribution of the added CO₂ between the atmosphere, oceans, and biosphere takes hundreds of years, and the removal of the added carbon from the short-term cycle by the long-term cycle takes thousands of years.

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