In the past one hundred and forty years, the average temperature of the globe has increased by approximately 0.6°C. (Zwiers, 200) More recently, the 1990s was the hottest decade that has been recorded during this one hundred and forty year period. At first glance, this change may not appear to be significant. However, this seemingly small increase in global mean temperatures has caused some important changes in our earth's landscape, in the 20th Century alone. Mean sea levels have increased by two millimeters annually, putting many low-lying nations in increasing danger during tropical storms. The incidence of tropical storms and other extreme weather events have dramatically increased. Temperature and precipitation shifts have forced many plants and animals to adjust their ranges upward in elevation and towards their respective poles. (Cunningham, 2000) Glaciers have been retreating at an alarming rate, and lake ice covers in the higher latitudes of the Northern Hemisphere last fourteen fewer days than they did at the beginning of the century. In the Northern Hemisphere, warming has caused earlier migration of birds, earlier breeding seasons, earlier plant flowering, and earlier emergence of insects. Growing seasons in the northern latitudes have been extended since the 1960s, and coral reefs in the southern latitudes have been bleached by the increased temperatures. (Cunningham, 200).
Many of these observations correlated with global climate change are projected continue into the next century. In fact, the Intergovernmental Panel on Climate Change, the world's authority on climate change, predicts that the 21st Century will see a warming much more drastic than that seen during the 20th Century. Global mean temperatures are projected to increase (depending on various scenarios) by a range of 1.4°C to 5.8°C, with a corresponding rise in sea levels of 9 millimeters to 880 millimeters.