A Virtual Field Trip Through Earth’s Dynamic Systems A01_CHRI5019_WT.indd 1 05/12/14 5:24 PM Exploring Earth’s Dynamic Systems Elemental Geosystems is organized around the natural flow of energy, materials, and in- formation, presenting subjects in the same sequence in which they occur in nature—an organic, holistic Earth systems approach that is unique in this discipline. Offering current examples and modern science, Elemental Geosystems combines a structured learning path, student-friendly writing, current applications, outstanding visuals, and a strong multi- media program for a truly unique physical geography experience. NEW! Chapter 8: Climate Change. Incorporating the latest climate change science and data, this new chapter covers paleoclimatology and mechanisms for past climatic change, climate feedbacks and the global carbon budget, the evidence and causes of present climate change, climate forecasts and models, and actions that we can take to moderate Earth’s changing climate. 244 Elemental Geosystems GEOSYSTEMSnow Climate Change 8 Greenhouse Gases Awaken in the Arctic n the subarctic and tundra climate re- A Positive Feedback Loop As sum- Igions of the Northern Hemisphere, per- mers become warmer in the Arctic, ennially frozen soils and sediment, known heat radiating through the ground as permafrost, cover about 24% of the land thaws the permafrost layers. Micro- area. With Arctic air temperatures curren- bial activity in these layers increases, tly rising at a rate more than two times that enhancing the breakdown of organ- of the midlatitudes, ground temperatures ic matter and releasing CO2 into the are increasing, causing permafrost thaw. atmosphere in a process known as This results in changes to land surfaces, microbial respiration. In anaerobic primarily sinking and slumping, that dam- (oxygen-free) environments, such age buildings, forests, and coastlines (Fig- as lakes and wetlands, the pro- ure GN 8.1). Permafrost thaw also leads to cess releases methane. Studies the decay of soil material, a process that show that thousands of methane releases vast amounts of carbon—in the seeps can develop under a single form of the greenhouse gases carbon di- lake, a huge amount when multi- oxide (CO2) and methane (CH4)—into the plied by hundreds of thousands of atmosphere. lakes across the northern latitudes (Figure GN 8.2). Carbon in Permafrost Soils Permafrost Carbon dioxide and methane is, by definition, soil and sediment that re- are major greenhouse gases, which main frozen for two or more consecutive absorb outgoing longwave radia- ▲Figure GN 8.2 Methane lies under years. It lies under a thin “active layer,” tion and radiate it back toward Earth, en- Arctic lakebeds and, like natural gas, is seasonally frozen ground that thaws every hancing the greenhouse effect and lead- highly flammable. [Todd Paris/Fairbanks/ summer to provide substrate for seasonal ing to atmospheric warming. Methane is University of Alaska/AP Images.] grasses and other plants that absorb especially important because, although CO from the atmosphere. In winter, the 2 its relative percentage in the atmosphere rate faster than Arctic air temperatures, active layer freezes, trapping plant and is small, it is far more effective than CO2 releasing vast amounts of “ancient” car- animal material before it can decompose at trapping atmospheric heat. Thus, a bon into the atmosphere. Scientists are completely. Over hundreds of thousands positive feedback loop forms: As tem- actively researching the locations and of years, this carbon-rich material has peratures rise, permafrost thaws, causing amounts of vulnerable permafrost, the become incorporated into permafrost a release of CO2 and CH4 into the atmo- current and projected rates of thaw, and and now makes up roughly half of all the sphere, which causes more warming, the potential impacts to the permafrost– A February 2014 storm caused large waves and flooding along the southern coast of England, near Newhaven. Ongoing research shows that organic matter stored in Earth’s soils— leading to more permafrost thaw. carbon positive feedback. The thawing the frequency of intense weather events is increasing with climate change. [Toby Melville/Reuters/Corbis.] twice the amount of carbon that is stored Arctic is one of many immediate concerns in the atmosphere. The latest estimate Melting Ground Ice In addition to frozen we discuss in this chapter regarding the of the amount of carbon stored in Arctic soil and sediment, permafrost contains causes and impacts of changing climate KEYLEARNINGconcepts permafrost soils is 1700 gigatonnes (or ground ice, which melts as the permafrost on Earth systems. 1700 billion tons). thaws. When the supporting structure provided by the ice is After reading the chapter, you should be able to: QUESTION AND EXPLORE: To learn about ▼Figure GN 8.1 Blocks of melting permafrost collapse removed, land surfaces • scientific tools used to study NASA’s Carbon in Arctic Reservoirs Vul- Describe into the Beaufort Sea, Alaska. [USGS Alaska Science Center.] collapse and slump. nerability Experiment (CARVE), which paleoclimatology. Subsurface soils are measures CO and CH gas emissions in then exposed to sun- 2 4 • Discuss several natural factors that influence Earth’s permafrost regions, go to http://science1. light, which speeds up climate and describe climate feedbacks, using nasa.gov/missions/carve/ (the mission microbial processes, examples. website) or http://www.nasa.gov/topics/ and to water erosion, earth/features/earth20130610.html#. • List the key lines of evidence for present global climate which moves organic UhwYVj_pxXJ (mission background and change and summarize the scientific evidence for carbon into streams early results). anthropogenic forcing of climate. and lakes, where it is • Discuss climate models and summarize some climate mobilized into the at- mosphere. Research projections. suggests that this pro- • Describe several mitigation measures to slow rates of cess may release bursts climate change. of CO2 and CH4 into the atmosphere, in contrast to the slower top-down melting of permafrost. 212 Elemental Geosystems Permafrost soils are now warming at a Water Use THEhumanDENOMINATOR 6 245 WATER RESOURCES IMPACT HUMANS HUMANS IMPACT WATER RESOURCES • Freshwater, stored in lakes, rivers, and groundwater, is a critical • Climate change affects lake depth, thermal structure, and resource for human society and life on Earth. associated organisms. M08_CHRI5019_08_SE_C08.indd 244 03/12/14• Drought 1:51 PM M08_CHRI5019_08_SE_C08.inddresults in water deficits, 245 decreasing regional water supplies • Water projects (dams and diversions) redistribute03/12/14 1:51 PMwater over and causing declines in agriculture. space and time. • Groundwater overuse and pollution depletes and degrades the 6a Desalination is an important resource, with side effects such as collapsed aquifers and saltwater supplement to water supplies in regions with large variations contamination. in rainfall throughout the year 6b The third largest reservoir and declining groundwater in the world, Lake Nasser reserves. This plant in is formed by the Aswan Barcelona, Spain, uses the High Dam on the Nile River process of reverse osmosis to in Egypt. Its water is used remove salts and impurities. for agricultural, industrial, and domestic purposes, as well as for hydropower. c NEW! The Human Denominator summarizes Human-Earth relationships, interactions, and challenges for the 21st century through dynamic visuals, including maps, photos, graphs, and diagrams. Blue Marble–Next Generation image shows December land surface topography and bathymetry. 6c Quadishaya Quadishaya Reservoir Reservoir 6d 0 5 10 MILES Euphrates 0 5 10 MILES Euphrates River River 0 5 10 KILOMETERS 0 5 10 KILOMETERS 160 150 140 September 7, 2006 130 The Itaipu Dam and power plant on the Paraná River bordering Brazil and Paraguay produces more 120 Reservoir level (m) electricity annually than the Three Gorges Dam in September 15, 2009 China. Itaipu Reservoir displaced over 10,000 people 2003 2004 2005Year 2006 2007 2008 2009 and submerged Guaira Falls, formerly the world’s Data from GRACE reveal a rapid decline in reservoir levels from 2006 to 2009 along the largest waterfall by volume. Euphrates River in the Middle East; Quadishaya Reservoir is an example. The graph shows the surface-level decline, with dates of the images marked. About 60% of the volume loss is attributed to groundwater withdrawals in the region. ISSUES FOR THE 21ST CENTURY • Maintaining adequate water quantity and quality will be a major issue. Desalination will increase to augment freshwater supplies. • Hydropower is a renewable energy resource; however, drought-related streamflow declines and drops in reservoir storage interfere with production. • Drought in some regions will intensify, with related pressure on ground- water and surface water supplies. A01_CHRI5019_WT.indd 2 M06_CHRI5019_08_SE_C06.indd 212 03/12/14 1:44 PM 05/12/14 5:24 PM Visualizing Processes & Landscapes . NEW! Geosystems in Action provide highly-visual presentations of core physical processes and critical chapter concepts. 386 Elemental Geosystems Chapter 12 River Systems 387 eandering channels curveeandering from side channels to side in curve a snakelike from side pattern to side and in usually a snakelike occur pattern where andlow-gradient usually occur streams where flow low-gradient through streams flow through Stream MeanderingStream Process Meandering Process Stream valley landscape: Stream valley