Global warming

There is concern that humans may be influencing the biosphere in other ways. You have probably heard of the greenhouse effect; this is a process that traps heat in the atmosphere. Without this process it would be too cold on Earth to live. In lesson 3 you learned about Venus. Do you remember that Venus' atmosphere is very thick and hot? This is because the atmosphere on Venus is made mostly of carbon dioxide. Carbon dioxide is particularly good at trapping heat and is a major factor in producing the greenhouse effect.

Many scientists are worried because burning products such as coal, natural gas, and oil adds carbon dioxide to the atmosphere. Since carbon dioxide absorbs heat, the atmosphere may become warmer and disrupt the normal climate and weather patterns. Since the late 1800s the level of carbon dioxide in the earth's atmosphere has increased by 30 percent. During the past century, the average temperature of the earth has increased by 1° F. If the increase continues, some scientists fear that there could be serious and permanent consequences. The warmer weather could cause polar caps to melt , which would cause sea levels to raise. During the last hundred years it is estimated that warmer temperatures have caused the sea level rise four to eight inches. The warmer water may cause other problems too. As you learned earlier, tropical storms begin over warm ocean water. Scientists worry that warmer oceans could result in more frequent and stronger tropical storms. In the U.S. that could mean more hurricanes.

Some scientists believe that there has always been a natural cycle of global warming and cooling, and they are not convinced that human activities can alter the cycle. Scientists are working to determine exactly what the consequences might be if we continue to add large amounts of carbon dioxide to the atmosphere.

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