Image above obtained from  http://www.cotf.edu/ete/modules/carbon/earthfire.html
 

            Facts:
                - Carbon (C) enters the biosphere during photosynthesis:
                                 CO2 + H2O ---> C6H12O6 + O2 + H2O
               - Carbon is returned to the biosphere in cellular respiration:
                             O2 +H2O + C6H12O6 ---> CO2 +H2O + energy

               Amount of CO2 during the year:
              - Every year there is a measurable difference in the
                concentration of atmospheric CO2 in phase with the seasons.
                For example, in winter there is almost no photosynthesis
                therefore there is a high concentration of CO2.
                - During the growing season there is a measurable differnece in the
                concentration of atmospheric CO2  over parts of each day. For
                example, at sunrise photosynthesis begins with the uptake of CO2,
                by afternoon plant respiration increases, at sunset photosynthesis
                stops so the concentration of CO2 in the atmosphere increases.

              Human induced changes in the global carbon cycle:
               - The Earth is getting warmer.
                - The 20th century has been the warmest in the last 600 years.
                - This century is about 1 degree Fahrenheit warmer than last
                century.
                - The balance of evidence suggests that burning of fossil fuel
                (eg. coal, oil, natural gas), which emits CO2 as a waste, is the
                 cause.
                - CO2 is a "Green House" gas - it traps heat at the Earth's surface.
                (H2O vapor and methane are also examples of green house gases)

            Signs that the climate is warming:
                - Plants start blooming 8 days earlier in spring than 11 years ago.
                - Birds from the United Kingom lay eggs earlier.
                - Buds on trees appear earlier and leaves fall later in the Northern
                  Hemisphere.
                - Alaska, North West Canada, and Siberia have warmed up as
                  much as 5 degrees Fahrenheit in the last 30 years.
 

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