Environmental Problems, Their Causes, and Sustainability 1

City 10–15%Grass 15–25%Bare sand 30–60%Oceans 5%Clouds 50–55%Snow 80–90%Forest 5%Figure 21-7 The albedo, or reflectivity of incoming solar energy,of different parts of the earth’s surface varies greatly.(Data from NOAA)Height above or belowpresent sea level (meters)into space. Much less sunlight is reflected by darkersurfaces such as forests, grass, cities, and oceans. Thusthe world’s coldest regions are part of the earth’s airconditioningsystem.A rise in the earth’s temperature can cause gradualmelting of some of the earth’s ice caps, floating ice,and mountain glaciers to melt. This would exposedarker and less reflective surfaces of water and landand result in a warmer troposphere. As more ice melts,the troposphere can become warmer, which meltsmore ice and increases the tropospheric temperatureeven moreIt is not known whether this shrinkage and thinningof floating sea ice is the result of natural polarclimate fluctuations, global warming caused by human-causedincreases in greenhouse gases, or a combinationof both factors—the last being the most likelyexplanation, according to many climate scientists. Regardlessof the cause, such changes can affect theearth’s temperatures and climate.Because it is floating, large-scale melting of ArcticOcean ice will not raise global sea levels—just as an icecube in a glass of water does not raise the water levelwhen it melts. However, according to researchers at theUniversity of California at Santa Cruz, as much as halfof the Arctic sea ice could disappear by 2050. If thishappens, it would shift the course of the storm-guidingjet stream northward. The researchers estimate thiswould reduce wintertime rain and snowfall by nearly athird over an area stretching from southern BritishColumbia to Mexico. The resulting drop in the SierraNevada snow pack would sharply reduce the springand summer water supply for states such as California.Many scientists believe that the biggest long-termclimate danger comes from Greenland. They are especiallyconcerned about partial or eventually completemelting of the land-based glaciers or ice sheets thatcover Greenland.If this occurred, as it did in a previous interglacialwarm period 110,000–130,000 years ago (Figure 21-8),average sea levels would rise by 7 meters (23 feet). In2002, glaciologist Konrad Steffen reported that icecovering about a third of Greenland’s total area ismelting at a much faster rate than at any time sincerecords have been kept. Researchers have calculatedthat a 3°C (5°F) rise in the earth’s average atmospherictemperature—within the range projected during thiscentury—would be enough eventually to melt the entireGreenland ice sheet. They estimate this wouldtake about 1,000 years but partial melting could acceleratean increase in average sea level during this century.This is an area that scientists will be watchingclosely.Would you like a preview of some of the effects ofrapid atmospheric warming over the next 25–30 years?Visit Alaska, where average winter temperatures haveincreased by 4°C (8°F)—since 1960 and year-roundtemperatures have risen by 3°C (5°F). Most of this increaseoccurred since 1976. The hottest year in Alaskanhistory was 2002, and the winter of 2003 was the secondwarmest on record.These warmer temperatures are melting glaciersand snow in parts of Alaska. Some of the permafrostunder arctic tundra soils is warming and melting. Thisreleases large amounts of CO 2 and CH 4 into the troposphere,which can accelerate tropospheric warming.The melting permafrost has caused buildings, roads,telephone and utility lines, and parts of the Trans-Alaska pipeline (Figure 17-9, p. 357) to sink, shift, andin some cases break up. In some parts of Alaska trees0−130Today’s sea level0−426250,000 200,000 150,000 100,000 50,000 0Years before present PresentHeight above or belowpresent sea level (feet)Figure 21-8 Changes in average sea level over the past 250,000years based on data from cores removed from the ocean. The comingand going of glacial periods (ice ages) largely determine therise and fall of sea level. As glaciers melted and retreated since thepeak of the last glacial period about 18,000 years ago, the earth’saverage sea level has risen about 125 meters (410 feet). (Adaptedfrom Tom Garrison, Oceanography: An Invitation to Marine Science,3/E, © 1998. Brooks/Cole.)468 CHAPTER 21 Climate Change and Ozone Loss