Environmental Problems, Their Causes, and Sustainability 1

Atmosphere(most carbon is in carbon dioxide)volcanic actionCombustionof fossilfuelsTerrestrialrocksLand food websProducers, consumers,decomposers, detritivoresSoil water(dissolved carbon)Peat,fossil fuelsally expose the limestone to the atmosphere and acidicprecipitation and make its carbon available to livingorganisms once again.How Are Human Activities Affectingthe Carbon Cycle? Messing with Nature’sThermostatCarbon dioxide produced by burning fossilfuels and clearing photosynthesizing vegetationfaster than it is replaced can increase theaverage temperature of the troposphere.Since 1800 and especially since 1950, we have been interveningin the earth’s carbon cycle in two ways thatadd carbon dioxide to the atmosphere. First, in someareas we clear trees and other plants that absorb CO 2through photosynthesis faster than they can growback. Second, we add large amounts of CO 2 by burningfossil fuels (Figure 4-30) and wood.Computer models of the earth’s climate systemssuggest that increased concentrations of atmosphericCO 2 and other gases we are adding to the atmospherecould enhance the planet’s natural greenhouse effect thathelps warm the lower atmosphere (troposphere) andthe earth’s surface (Figure 4-9). The resulting globalwarming could disrupt global food production andCO 2 emissions from fossil fuels(billion metric tons of caron equivalent)141312111098765432HighprojectionLowprojection101850 1900 1950 2000 2030YearFigure 4-30 Natural capital degradation: human interferencein the global carbon cycle from carbon dioxide emissions whenfossil fuels are burned, 1850 to 2001 and projections to 2030(dashed lines). (Data from UN Environment Programme, BritishPetroleum, International Energy Agency, and U.S. Departmentof Energy)http://biology.brookscole.com/miller1479