Environmental Problems, Their Causes, and Sustainability 1

Average surface temperature (°C)Average temperature over past 900,000 years17161514131211109900 800700 600 500 400 300 200 100 PresentThousands of years agoTemperature change (°C)210−1−2−3−4−5Temperature change over past 22,000 yearsAgriculture establishedEnd oflast iceage20,000 10,000Average temperature over past10,000 years = 15°C (59°F)2,000 1,000 200 100 NowYears agoTemperature change (°C)Temperature change over past 1,000 years1.00.50.0−0.5−1.01000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2101YearAverage surface temperature (°C)15.014.814.614.414.214.013.813.61860 1880Average temperature over past 130 years1900 1920 1940 1960 1980 2000 2020YearFigure 21-2 Estimated changes in the average global temperature of the atmosphere near the earth’ssurface over different periods of time. Past temperature changes are estimated by analysis of radioisotopes inrocks and fossils, plankton and radioisotopes in ocean sediments, ice cores from ancient glaciers, temperaturemeasurements at different depths in boreholes drilled deep into the earth’s surface, pollen from lake bottomsand bogs, tree rings, historical records, and temperature measurements (since 1861). (Data from GoddardInstitute for Space Studies, Intergovernmental Panel on Climate Change, National Academy of Sciences,National Aeronautics and Space Agency, National Center for Atmospheric Research, and National Oceanicand Atmospheric Administration)ical Organization established the IntergovernmentalPanel on Climate Change (IPCC) to document pastclimate change and project future climate change. TheIPCC is a network of over 2,000 leading climate expertsfrom 70 nations.Panels of scientists from the U.S. National Academyof Sciences and the American Geophysical Union(AGU) have also evaluated possible future climatechanges. In addition, the U.S. Congress created theU.S. Global Change Research Program (USGCRP ) in1990 to project future climate changes and the potentialimpacts.Recall that science can never give us absolute certaintyor proof. Instead, it establishes levels of certaintyor probability that a scientific model or theory istrue. The IPCC expresses its conclusions and projectionsin probabilities using several levels of certainty:virtually certain (more than 99% probability), very likely(90–99% probability), and likely (66–90% probability).Throughout this chapter I use these categories to describeIPCC conclusions and projections about atmospherictemperature changes and their possible affectson climate.Figure 21-3 Ice cores such as this one extracted by drillingdeep holes in ancient glaciers at various sites in antarctica andGreenland can be analyzed to obtain information about past climates.http://biology.brookscole.com/miller14463