The woman gathering fuelwood in the Sudan senses a difference. She has survived two extremely dry years and then, in only three days, sees a year's rain fall. The American, Australian, and African farmers who have seen deep droughts and big rains crush their crops again and again in the last 10 years, can feel a difference in the soil and smell a difference in the air. The Bangladeshi boatman, who sees the "once-in-a-century" typhoon surge out of the Bay of Bengal twice in twenty years senses that the weather has changed since his childhood. The South Pacific ecologist of coral reefs knows that something significant has disturbed the seabed; she sees large masses of dying coral. The Swiss ski resort owners, who wait through two long winters without sufficient snow on which to ski, all know something is different. But what is it? A string of random independent events? A passing phase? Or are the collective experiences of people all over the world an indicator of a profound and lasting change, a global climate change?

-taken from Confronting Climate Change: Risks, Implications, and Responses

Change is in the air. The warmest years on record have all occurred since 1990. Extreme climactic events are increasing in intensity and frequency. Glaciers are melting. Sea levels are rising. While we have yet to see plagues of frogs and locusts, it is clear to scientists, researchers, and policymakers that the earth is going through major climatic change. While this concept is not a new phenomenon--- climate on Earth has experienced natural variation many times in the last two billion years--- something is different this time. The composition of our atmosphere is changing at an unprecedented rate, and many researchers claim that human activities such as deforestation and the emission of "greenhouse gases" such as carbon dioxide and chloroflourocarbons (CFCs) into the atmosphere are to blame for these present and inevitably for the future changes in our climate. Skeptics argue that these activities enhance the greenhouse effect, a natural process that keeps the temperature of Earth warm and hospitable to humans, so as to cause an additional, human-induced, greenhouse (or 'global') warming. The reliability of the climate models that communicate this climate change has also been questioned by these skeptics. While the enhanced greenhouse effect cannot be definitively tied to greenhouse gas emissions just yet, the circumstantial evidence is overwhelming, and risk of further danger is severe. The causes and impacts of global climate change, human-induced or not, touch every aspect of human society, making the issue of global warming not merely a scientific, political, or economic concern, but a human issue requiring immediate action.