Human Alteration of the Carbon Cycle
Recently, scientists have studied both short- and long-term measurements of atmospheric CO2 levels. Their data revealed that human activities are significantly altering the natural carbon cycle. Since the beginning of the industrial revolution, human activities such as the burning of fossil fuels and deforestation have accelerated, and both have contributed to a long-term rise in atmospheric CO2. Burning oil and coal releases carbon into the atmosphere far more rapidly than it is being removed, and this imbalance causes atmospheric carbon dioxide concentrations to increase. In addition, by clearing forests, we reduce the ability of photosynthesis to remove CO2 from the atmosphere, also resulting in a net increase. Because of these human activities, atmospheric carbon dioxide concentrations are higher today than they have been over the last half-million years or longer. Because CO2 increases the atmosphere’s ability to hold heat, it has been called a “greenhouse gas.” Without substantive changes in global patterns of fossil fuel consumption and deforestation, warming trends are likely to continue. The best scientific estimate is that global mean temperature will increase between 1.4 and 5.8 degrees C over the next century as a result of increases in atmospheric CO2 and other greenhouse gases. This kind of increase in global temperature would cause significant rise in average sea-level (0.09-0.88 meters), exposing low-lying coastal cities or cities located by tidal rivers. Even without the changes in climate, however, increased concentrations of CO2 could have an important impact on patterns of plant growth worldwide. Because some species of plants respond more favourably to increases in CO2 than others, scientists believe we may see distinct shifts in plant species as a result of increasing atmospheric CO2 concentrations, even without any change in temperature. For example, under elevated CO2 conditions, shrubs are thought...
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