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 CO2 from the atmosphere during photosynthesis, also called primary production, and release O2 back into the atmosphere.

CO2 CO2

The ocean is the largest sink of Carbon Dioxide. Another major exchange of CO2 occurs between the oceans and the atmosphere. The dissolved CO2 in the oceans is used by marine biota in photosynthesis. The ocean is the largest sink of Carbon Dioxide. CO2

THE CARBON CYCLE Photosynthesis – producers take in CO2 from atmosphere. Respiration – aerobic organisms release CO2 into atmosphere. Decay – as a result of decay CO2 released into atmosphere. Combustion – Burning of fossil fuels release CO2 into atmosphere.

The uptake and return of CO2 are not in balance The carbon dioxide content of the atmosphere is gradually and steadily increasing. The increase in CO2 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 CO2 content until 300 years ago.

THE CARBON CYCLE Since measurements of atmospheric CO2 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 CO2 CO2

The Complete Carbon Cycle

THE GREENHOUSE EFFECT & GLOBAL WARMING Despite these "sinks" for our greatly increased CO2 production, the concentration of atmospheric CO2 continues to rise? Should we be worried? Carbon dioxide is transparent to light but rather opaque (not clear) to heat rays. Therefore, CO2 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. -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 CO2 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.