THE CARBON CYCLE THE CARBON CYCLE The movement

THE CARBON CYCLE

THE CARBON CYCLE The movement of carbon, in its many forms, between the biosphere, atmosphere, oceans, and geosphere is described by the carbon cycle. In the cycle there are various sinks, or stores, of carbon and processes by which the various sinks exchange carbon. These processes of exchange include respiration, burning, combustion, decomposition, erosion, etc.

THE CARBON CYCLE Over 300 million years ago (Carboniferous Period), large amounts of carbon accumulated in carbon sinks as coal, peat, oils and natural gas.

THE CARBON CYCLE Coal, peat, and natural gas are fossil fuels. It took millions of years to make these fuels, but we are burning them all up in a few hundred years.

THE CARBON CYCLE We are all familiar with how the atmosphere and vegetation exchange carbon (photosynthesis and respiration). Plants absorb CO 2 from the atmosphere during photosynthesis, also called primary production, and release O 2 back into the atmosphere.

CO 2

Another major exchange of CO 2 occurs between the oceans and the atmosphere. The dissolved CO 2 in the oceans is used by marine biota in photosynthesis. The ocean is the largest sink of Carbon Dioxide. CO 2

THE CARBON CYCLE Photosynthesis – producers take in CO 2 from atmosphere. Respiration – aerobic organisms release CO 2 into atmosphere. Decay – as a result of decay CO 2 released into atmosphere. Combustion – Burning of fossil fuels release CO 2 into atmosphere.

The uptake and return of CO 2 are not in balance The carbon dioxide content of the atmosphere is gradually and steadily increasing. The increase in CO 2 probably began with the start of the industrial revolution. Samples of air trapped over the centuries in the glacial ice of Greenland showed no change in CO 2 content until 300 years ago.

THE CARBON CYCLE Since measurements of atmospheric CO 2 began late in the nineteenth century, its concentration has risen over 20%. This increase is surely caused by human activities: burning fossil fuels (coal, oil, natural gas) returns carbon to the atmosphere, carbon that has been locked within the earth for millions of years. clearing and burning of forests, especially in the tropics. In recent decades, large areas of the Amazon rain forest have been cleared for agriculture and cattle grazing.

Human Activities Increasing Carbon Dioxide in the Atmosphere CO 2

The Complete Carbon Cycle CO 2 CO 2

THE GREENHOUSE EFFECT & GLOBAL WARMING Despite these "sinks" for our greatly increased CO 2 production, the concentration of atmospheric CO 2 continues to rise? Should we be worried? Carbon dioxide is transparent to light but rather opaque (not clear) to heat rays. Therefore, CO 2 in the atmosphere slows the radiation of heat from the earth back into space — the "greenhouse effect".

GLOBAL WARMING Has the increase in carbon dioxide led to global warming? Average temperatures do seem to have increased slightly (~0. 6°C) in the last century. Some evidence comes from: Careful monitoring of both ocean and land temperatures.

MORE EVIDENCE -Many glaciers and ice sheets are receding. -Woody shrubs are now growing in areas of northern Alaska that 50 years ago were barren tundra. -Many angiosperms in temperate climates are flowering earlier in the spring than they used to. -Many species of birds and butterflies are moving north and breeding earlier in the spring.

GLOBAL WARMING Will continued increase in carbon dioxide lead to more global warming and, if so, how much? At this point, the answer depends on what assumptions you plug into your computer models. But as the different models have been improved, they seem to be converging on a consensus: a doubling of the CO 2 concentration (expected by the end of this century) will cause the earth to warm somewhere in the range of 2. 5– 3. 5°C.

Assignment On page 35 of your booklet there are 5 questions. In groups answer these questions on chart paper and be prepared to present your group’s answers to the class.