Greenhouse Gas Emissions and Climate ChangeCarbon dioxide and other "greenhouse gases" trap heat in the atmosphere and raise average global surface temperatures. Emissions of carbon dioxide grew 12-fold between 1900 and 2000, from 534 million metric tons per year in 1900 to 6.59 billion metric tons in 1997.58 In the same period, human population nearly quadrupled, from 1.6 billion to 6.1 billion, progressively consuming greater quantities of fossil fuels—oil, gas and coal. Expanded agriculture, destruction of forests and increased production of certain chemicals also increase greenhouse gases in the atmosphere. It is unlikely that the human population could ever have reached its present size without the energy provided by fossil fuels. Conversely, the needs of the growing population have provided an ever-expanding market for exploration and production.59
Climate change will have a serious impact. The Intergovernmental Panel on Climate Change (IPCC) estimates that the earth's atmosphere will warm by as much as 5.8 degrees Celsius over the coming century, a rate unmatched over the past 10,000 years.60 The IPCC's "best estimate" scenario projects a sea-level rise of about half a metre by 2100 (with a range of 15 to 95 centimetres), substantially greater than the increase over the last century.61 The human and ecological impacts of rising oceans include increased flooding, coastal erosion, salinization of aquifers, and loss of coastal cropland, wetlands and living space. The intensity and frequency of hurricanes and other hazardous weather may also increase, endangering the growing human population in coastal areas.62 Rising global surface temperatures and changes in precipitation magnitude, intensity and geographical distribution may well redraw the world renewable resources map. Whether or not these climatic changes affect net global agricultural production, they are almost certain to shift productivity among regions and countries, and within nations.63 For example, recent projections suggest that while total U.S. agriculture production may not diminish, certain regions of the country are likely to suffer substantially relative to others, as a result of changes in precipitation and temperature.64 Climate change policy will have to address changing regional and national fortunes, as well as the global economic and biological impact.65 A warming climate also poses a significant public health threat. The redistribution of precipitation would markedly increase the number of people living in regions under extreme water stress—a problem compounded by increasing population.66 The geographical range of temperature-sensitive tropical diseases, such as malaria and dengue fever, would also expand.67 Higher average temperatures mean longer and more-intense heat waves, with a corresponding rise in heat-related health problems. The combined effects of population growth and climate change could produce regional resource shortages, which in turn could result in the exploitation of environmentally sensitive areas such as hillsides, flood plains, coastal areas and wetlands.68 These conditions may also increase environmental refugees, international economic migration and associated socio-political challenges.69 Climate and environmental policy should address the geographical distribution and movement of people in the 21st century, as well as their absolute numbers.70 |
