Global climate involves cycles of matter across the biosphere and everything modern humans do—from cutting and burning forests to manufacturing, driving cars, and generating electricity. The most reliable current information available on this subject comes from the 2007 report of the Intergovernmental Panel On Climate Change (IPCC). The IPCC is an international organization established in 1988 to provide the best possible scientific information on climate change. IPCC reports contain data and analyses that have been agreed upon and accepted by 2500 climate scientists from around the world and the governments participating in the study.
Recognizing a Problem: Global Warming The IPCC report confirms earlier observations that global temperatures are rising. This increase in average temperature is called global warming. Remember that winds and ocean currents, which are driven by differences in temperature across the biosphere, shape climate. Given this link between temperature and climate, it isn't surprising that the IPCC report discusses more than warming. The report also discusses climate change—changes in patterns of temperature, rainfall, and other physical environmental factors that can result from global warming. There are many lines of evidence, both physical and biological, that have contributed to our current understanding of the climate change issue.
• Physical Evidence Physical evidence of global warming comes from several sources. The graphs in Figure 6–30, taken from data in the 2007 IPCC report, show that Earth's temperatures are getting warmer, its sea ice is melting, and its sea levels are rising. Eleven of the twelve years between 1995 and 2006 were among the warmest years since temperature recording began in 1850. Between 1906 and 2005, Earth's average global temperature rose 0.74°C. The largest changes are occurring in and near the Arctic Circle. Average temperatures in Alaska, for example, increased 2.4°C over the last 50 years. Sea level has risen since 1961 at a rate of 1.8 mm each year. This increase is caused by warmer water expanding and by melting glaciers, ice caps, and polar ice sheets. Satellite data confirm that arctic sea ice, glaciers, and snow cover are decreasing.
FIGURE 6–30 A Warming Earth