According to the Intergovernmental Panel on Climate Change (2007), “Warming of the climate system is unequivocal” . That study concludes that most of the warming over the last 50 years is attributable to human activities. As the earth warms, extreme heat conditions are expected to affect both human health and ecosystems. Some damage to humans is caused directly by increased heat, as shown by the heat waves that resulted in thousands of deaths in Europe in the summer of 2003. Human health can also be affected by pollutants, such as smog, that are exacerbated by warmer temperatures. Rising sea levels (as warmer water expands and previously frozen sources such as glaciers melt), coupled with an increase in storm intensity, are expected to flood coastal communities. Ecosystems will be subjected to unaccustomed temperatures; some will adapt by migrating to new areas, but others may not be able to adapt in time. While these processes have already begun, they will intensify slowly throughout the century. 1 Sources: David Webster, Anncorinne Freter, and Nancy Golin. COPAN: THE RISE AND FALL OF AN ANCIENT MAYA KINGDOM. (Fort Worth: Harcourt Brace Publishers, 2000); and Brander, J. A. and M. S. Taylor (1998). “The Simple Economics of Easter Island: A Ricardo - Malthus Model of Renewable Resource Use,” THE AMERICAN ECONOMIC REVIEW, 88(1), pp. 119– 138.
5 Climate change also has an important moral dimension. Due to their more limited adaptation capabilities many Developing countries that have produced relatively small amounts of greenhouse gases are expected to be the hardest hit as the climate changes. Dealing with climate change will require a coordinated international response. That is a significant challenge to a world system where the nation-state reigns supreme and international organizations are relatively weak. 1.1.2 Water Accessibility Another class of threats is posed by the interaction of a rising demand for resources because it is vital to life. According to the United Nations about 40 percent of the world’s population lives in areas with moderate-to-high water stress. “ Moderate stress ” is defined in the U.N. Assessment of Freshwater Resources as “human consumption of more than 20 percent of all accessible renewable freshwater resources ,” whereas “ Severe stress ” denotes consumption greater than 40 percent.) By 2025, it is estimated that about two- thirds of the world’s population— about 5.5 billion people — will live in areas facing either moderate or severe water stress. This stress is not uniformly distributed around the globe . For example, in the United States, Mexico, China, and India, groundwater is being consumed faster than it is being replenished and aquifer levels are steadily falling. Some rivers, such as the Colorado in the western United States and the Yellow in China, often run dry before they reach the sea.