Global Warming

            Global warming is a critical issue that concerns many people. The greatest problem that we have is that we are uncertain about the effects that global warming will cause. We are not sure what will happen to the climate and how things will be able to adapt to it. The uncertainty is due to the fact we cannot tell if global warming has had any direct environmental impact, because human activity has been largely responsible for the environmental destruction.
             The average surface air temperature has increased by about 0.6 degrees Celsius in the last century. Interestingly, this occurred in three phases: a relatively rapid rise of 0.4 degrees between about 1910 and 1940, a surprising plateau between 1940 and 1975, and another rise of about 0.2 degrees Celsius between 1975 and the 1990's. Nine of the eleven hottest years in the twentieth century have occurred in the last ten years. In addition, studies done on tree rings, corals, ice cores, and historical data prove that the 1990's are the warmest decade in at least the last 1000 years. The Intergovernmental Panel on Climate Change foresees an increase of one degree Celsius to 3.5 degrees Celsius in the global mean temperature by the year 2100. They have also forecasted a rise of about forty centimeters in the sea level by the year 2100.
             Not only do temperature readings show that the temperature is rising but also environmental signals have occurred. The migration of plants to higher altitudes has been documented on numerous peaks in the European Alps, Alaska, Sierra Nevada and New Zealand. Also, since 1970 the lowest level at which freezing occurs has ascended about 150 meters higher in mountains in tropical latitudes. Many glaciers have been melting, such as the montane glaciers in Alaska.
             If the greenhouse effect did not take place, the surface temperature would be near negative eighteen degrees Celsius, instead of the normal fifteen degrees Celsius.