Environmental Problems, Their Causes, and Sustainability 1

These possibilities were affirmed by a 2003 analysiscarried out by Peter Schwartz and Doug Randallfor the Department of Defense. They also projectedwidespread rioting and regional conflict in some countriesfaced with dwindling food, water, and energysupplies. The authors concluded that global warmingmust “be viewed as a serious threat to global stabilityand should be elevated beyond a scientific debate to aU.S. national security concern.”21-5 FACTORS AFFECTING THEEARTH’S TEMPERATUREScientists have identified a number of natural and human-influencedfactors that might amplify (positivefeedback) or dampen (negative feedback) projectedchanges in the average temperature of the troposphere.The fairly wide range of projected future temperaturechanges shown in Figure 21-11 results fromincluding what is known about these factors in climatemodels. Let us examine some possible wildcards that could help or make matters worse or betterduring this century.Can the Oceans Store More CO 2 and Heat?We Do Not KnowThere is uncertainty about how much CO 2and heat the oceans can remove from thetroposphere and how long they might remainin the oceans.The oceans help moderate the earth’s average surfacetemperature by removing about 29% of the excess CO 2we pump into the atmosphere as part of the global car-bon cycle. They also absorb heat from the atmosphereand slowly transfer some of it to the deep ocean, whereit is removed from the climate system for long but unknownperiods of time (Figure 21-9).Oocean currents on the surface and deep down areconnected and act like a gigantic conveyor belt to storeCO 2 and heat in the deep sea and to transfer hot andcold water from the tropics to the poles (Figure 21-12and Figure 6-6, p. 106).Scientists do not know how rapidly heat absorbedby the ocean from the troposphere can be transferredto the deep ocean by such currents and other mixingprocesses. They also do not know whether, over thenext few decades, the oceans will release some of theirstored heat and dissolved CO 2 into the troposphere,thereby amplifying its global warming.Evidence suggests that large changes in the speedof the ocean currents in this conveyor belt, and itsstopping and starting, contributed to wild swings innorthern hemisphere temperatures during past iceages. Scientists are trying to learn more about howthese currents operate to evaluate the likelihood of theloop slowing down or stalling during this century andthe effects this might have on regional and global atmospherictemperatures.In 2003 a group of physical oceanographers, includingSydney Levitus of the National Oceanic andAtmospheric Administration (NOAA) and Ruth Curryof the Woods Hole Oceanographic Institute, announcedthe results of a compilation of millions of observationsand measurements of the Atlantic Ocean from pole topole. Their analysis indicated that tropical oceans arenow much saltier and oceans closer to the poles are lesssalty than they were 40 years ago. In other words, duringthis period fresh water has been lost from the lowlatitudes and added at high latitudes.Figure 21-12 Natural capital: a connected loop of shallowand deep ocean currents stores CO 2 in thedeep sea and transmits warm and cool water tovarious parts of the earth. It occurs whenocean water in the North Atlantic near Icelandis dense enough (because of itssalt content and cold temperature) tosink to the ocean bottom, flow southward,and then eastward to well upin the warmer Pacific. Then a shallowerreturn current aided by windsbrings warmer and less salty—andthus less dense—water to the Atlantic,which can then cool and sinkto begin the cycle again. A warmerplanet would be a rainier one, which,coupled with melting glaciers, would increasethe amount of fresh water flowing intothe North Atlantic. This could slow or even jamthe loop by diluting the salt water and making it morebuoyant (less dense) and less prone to sinking.GreenlandCold WaterAntarcticaWarm Water472 CHAPTER 21 Climate Change and Ozone Loss