Additional Reading 17 many aspects of.hydrology.imatol rainfall,soil carbon,consumption of plants ge m.Man ninlega the state factors tht co th nd rates of of tems?What are the str roaches,process understanding,and global of the state factor appro this Most ecosystems ultimately acquire their d What is the difference between state factors energy from the sun and their materials from and interactive controls?If you were asked the atmosphere and rock minerals.The energy to write a management plan for a region, and materials are transferred among compo- why would you treat a state factor and nents within the ecosystem and are ther an interactive control differently in your released to the environment.The essential plan? biotic components of ecosystems include 5.Using a forest or a lake as an example plants,which bring carbon and energy into the explain how climatic warming or the harvest ecosystem;decomposers, which break down of trees or fish by people might change the dead organic matter CO2 and nutri controls How might these ents, nges m trol alter the ials ses h sitive and neg tive f edbacks t responses o spher ses are controlled by set of rela tively independent state factors(climate.pa Additional reading and by a gre ing resource supply,modulators,disturbance Chapin.FS.III.M.S.Torn.and M.Tateno.1996.Prin regime.functional types of organisms.and human activities)that are the immediate con A Histo trols over ecosystem processes.The interactive e c controls both respond to and affect ecosystem ParBs.Yale University Press.New Haven.CT processes.The stability and resilience of eco- systems depend on the strength of negative eve intain the characteristics of 7 ecosystems】 current state. of Ecosystem Ecology.Rutgers University Press New Brunswick,NJ Jenny,H.1980. Review Questions n RL1942.The t ecology.Ecology 23:399-418. c-dynamic aspectsof Schlesinger,W.H.1997.Biogeochemistry:An Ana from a commu ysis of Global Change.Academic Press,San mental questions can be addressed by ecosystem ecology that are not readily Sousa.W.P.1985.The role of disturbance in natural addressed by population or community communities. Annual Review of Ecology and -391 ecology? 2.What is the difference between a pool and a ansley.A etational flux?Which of the following are pools and Vitousek.PM.1994.Beyond global warming which are fluxes:plants.plant respiration. Ecology and global change.Ecology 75:1861-1876
Additional Reading 17 many aspects of ecology, hydrology, climatology, and geology and contributes to current efforts to understand Earth as an integrated system. Many unresolved problems in ecosystem ecology require an integration of systems approaches, process understanding, and global analysis. Most ecosystems ultimately acquire their energy from the sun and their materials from the atmosphere and rock minerals. The energy and materials are transferred among components within the ecosystem and are then released to the environment. The essential biotic components of ecosystems include plants, which bring carbon and energy into the ecosystem; decomposers, which break down dead organic matter and release CO2 and nutrients; and animals, which transfer energy and materials within ecosystems and modulate the activity of plants and decomposers. The essential abiotic components of ecosystems are the atmosphere, water, and rock minerals. Ecosystem processes are controlled by a set of relatively independent state factors (climate, parent material, topography, potential biota, and time) and by a group of interactive controls (including resource supply, modulators, disturbance regime, functional types of organisms, and human activities) that are the immediate controls over ecosystem processes. The interactive controls both respond to and affect ecosystem processes. The stability and resilience of ecosystems depend on the strength of negative feedbacks that maintain the characteristics of ecosystems in their current state. Review Questions 1. What is an ecosystem? How does it differ from a community? What kinds of environmental questions can be addressed by ecosystem ecology that are not readily addressed by population or community ecology? 2. What is the difference between a pool and a flux? Which of the following are pools and which are fluxes: plants, plant respiration, rainfall, soil carbon, consumption of plants by animals? 3. What are the state factors that control the structure and rates of processes in ecosystems? What are the strengths and limitations of the state factor approach to answering this question. 4. What is the difference between state factors and interactive controls? If you were asked to write a management plan for a region, why would you treat a state factor and an interactive control differently in your plan? 5. Using a forest or a lake as an example, explain how climatic warming or the harvest of trees or fish by people might change the major interactive controls. How might these changes in controls alter the structure of or processes in these ecosystems? 6. Use examples to show how positive and negative feedbacks might affect the responses of an ecosystem to climatic change. Additional Reading Chapin, F.S. III, M.S. Torn, and M. Tateno. 1996. Principles of ecosystem sustainability. American Naturalist 148:1016–1037. Golley, F.B. 1993. A History of the Ecosystem Concept in Ecology: More Than the Sum of the Parts. Yale University Press, New Haven, CT. Gorham, E. 1991. Biogeochemistry: Its origins and development. Biogeochemistry 13:199–239. Hagen, J.B. 1992. An Entangled Bank: The Origins of Ecosystem Ecology. Rutgers University Press, New Brunswick, NJ. Jenny, H. 1980. The Soil Resources: Origin and Behavior. Springer-Verlag, New York. Lindeman, R.L. 1942.The trophic-dynamic aspects of ecology. Ecology 23:399–418. Schlesinger, W.H. 1997. Biogeochemistry: An Analysis of Global Change. Academic Press, San Diego. Sousa, W.P. 1985. The role of disturbance in natural communities. Annual Review of Ecology and Systematics 15:353–391. Tansley,A.G. 1935.The use and abuse of vegetational concepts and terms. Ecology 16:284–307. Vitousek, P.M. 1994. Beyond global warming: Ecology and global change. Ecology 75:1861–1876
2 Earth's Climate System Climate is the state factor that most strongly governs the global distribution of terrestrial biomes.This chapte vides a ral backe nd on the funct of the climate system and and land. Introduction Climate exerts a key control over the distri- bution of Earth's ecosystems. lemperature Earth's Energy Budget gical The ates ntrol The balan e bet s the ween in pro e es m energy a d organi rth's cli m. of ocks and the ergy det 0p四 of soils nd I ate Th sses (see Chapter 3).Under- sun is the s all of Earth standing the causes of temporal and spa erature of a body dete variation in climate is therefore critical to the wavelengths of energy emitted.The high understanding the global pattern of ecosystem temperature of the sun(6000K)results in emis. processes. sions of high-energy shortwave radiation with Climate and climate variability are deter- wavelengths of 300 to 3000nm(Fig.2.1).These mined by the amount of incoming solar radia- include visible(39%of the total),near-infrared tion,the chemical composition and dynamics of (53%),and ultraviolet (UV)radiation (8%) he surface characteristics On average,about 31%of the incoming short ea bac K to space,due to oceans innue the tran d m 10o片a1 ture a the and (7% This nty in (Fig.2.2) er 2 ese the b nd lan uds energy to pr mospher
Introduction Climate exerts a key control over the distribution of Earth’s ecosystems. Temperature and water availability determine the rates at which many biological and chemical reactions can occur. These reaction rates control critical ecosystem processes, such as the production of organic matter by plants and its decomposition by microbes. Climate also controls the weathering of rocks and the development of soils, which in turn influence ecosystem processes (see Chapter 3). Understanding the causes of temporal and spatial variation in climate is therefore critical to understanding the global pattern of ecosystem processes. Climate and climate variability are determined by the amount of incoming solar radiation, the chemical composition and dynamics of the atmosphere, and the surface characteristics of Earth.The circulation of the atmosphere and oceans influences the transfer of heat and moisture around the planet and thus strongly influences climate patterns and their variability in space and time. This chapter describes the global energy budget and outlines the roles that the atmosphere, oceans, and land surface play in the redistribution of energy to produce observed patterns of climate and ecosystem distribution. Earth’s Energy Budget The balance between incoming and outgoing radiation determines the energy available to drive Earth’s climate system. An understanding of the components of Earth’s energy budget provides a basis for determining the causes of recent and long-term changes in climate. The sun is the source of virtually all of Earth’s energy. The temperature of a body determines the wavelengths of energy emitted. The high temperature of the sun (6000 K) results in emissions of high-energy shortwave radiation with wavelengths of 300 to 3000 nm (Fig. 2.1). These include visible (39% of the total), near-infrared (53%), and ultraviolet (UV) radiation (8%). On average, about 31% of the incoming shortwave radiation is reflected back to space, due to backscatter (reflection) from clouds (16%); air molecules, dust, and haze (7%); and Earth’s surface (8%) (Fig. 2.2). Another 20% of the incoming shortwave radiation is absorbed by the atmosphere, especially by ozone in the upper atmosphere and by clouds and water vapor in the lower atmosphere. The remaining 2 Earth’s Climate System Climate is the state factor that most strongly governs the global distribution of terrestrial biomes. This chapter provides a general background on the functioning of the climate system and its interactions with atmospheric chemistry, oceans, and land. 18
Earth's Energy Budget 19 transfer of heat to the air from the warm surtace to the cooler overlying atmosphere (sen energ 1os)(g2 2).Heat abso rbeaemt from the sur evapor tes pr Although the atmosnhere transmits abou half of the incoming shortwave radiation to Earth's surface,it absorbs 90%of the longwave Terrestrial outgoing radiation (infrared)radiation emitted by the surface (Fig.2.2).Water vapor,carbon dioxide (CO2) 15 20 methane (CH),nitrous oxide (N2O),and Visible region industrial products like chlorofluorocarbons (CFCs)effectively absorb longwave radiation CH4 (Fig.2.1).The energy absorbed by thes N2O radiatively active gases is reradiated in all a longwave radiation (Fig. O2 and O3 e portio that is direc back to CO2 ming th P gree H20 ph longwave-abs Atmosphere than it is 5 10 20 2 today and would probably not rt life Wavelength(um) Radiation absorbed by clouds and radiatively FiGURE 2.1.The strial rad the major radiatively active gases and of the total (Fig.2.2). atmosphere.These spectra show that the atmosphere Long-term records of atmospheric gases. effectively thar obtained from atmospheric measurements made since the 1950s and from air bubbles heated from below (Sturman and Tapper 1996.Barry trapped in glacial ice,demonstrate large in- and Chorley 1970.) creases in the major radiatively active gases (Co CH.N.O.and FCs)since 5.31 str anin d fe y,a tilized es of in a state of radiativ of the lo it rolo as it absorbs.On ation emitted by Earth is tra ed hy the at average.Earth emits 79%of the absorbed phere,enhancing the greenhouse effect and energy as low-energy longwave radiation (3000 causing the surface temperature of Earth to to 30,000nm),due to its relatively low surface increase temperature (288K).The remaining energy is The globally averaged energy budget out- transferred from earth's surface to the atmos- lined above gives us a sense of the critical phere by the evaporation of water(latent heat factors controlling the global climate system. flux)(16%of terrestrial energy loss)or by the Regional climates,however,reflect spatial
Earth’s Energy Budget 19 49% reaches Earth’s surface as direct or diffuse radiation and is absorbed. Over time scales of a year or more, Earth is in a state of radiative equilibrium, meaning that it releases as much energy as it absorbs. On average, Earth emits 79% of the absorbed energy as low-energy longwave radiation (3000 to 30,000 nm), due to its relatively low surface temperature (288 K). The remaining energy is transferred from Earth’s surface to the atmosphere by the evaporation of water (latent heat flux) (16% of terrestrial energy loss) or by the transfer of heat to the air from the warm surface to the cooler overlying atmosphere (sensible heat flux) (5% of terrestrial energy loss) (Fig. 2.2). Heat absorbed from the surface when water evaporates is subsequently released to the atmosphere when water vapor condenses, resulting in formation of clouds and precipitation. Although the atmosphere transmits about half of the incoming shortwave radiation to Earth’s surface, it absorbs 90% of the longwave (infrared) radiation emitted by the surface (Fig. 2.2). Water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and industrial products like chlorofluorocarbons (CFCs) effectively absorb longwave radiation (Fig. 2.1). The energy absorbed by these radiatively active gases is reradiated in all directions as longwave radiation (Fig. 2.2). The portion that is directed back toward the surface contributes to the warming of the planet, a phenomenon know as the greenhouse effect. Without a longwave-absorbing atmosphere, the mean temperature at Earth’s surface would be about 33°C lower than it is today and would probably not support life. Radiation absorbed by clouds and radiatively active gases is also emitted back to space, balancing the incoming shortwave radiation (Fig. 2.2). Long-term records of atmospheric gases, obtained from atmospheric measurements made since the 1950s and from air bubbles trapped in glacial ice, demonstrate large increases in the major radiatively active gases (CO2, CH4, N2O, and CFCs) since the beginning of the Industrial Revolution 150 years ago (see Fig. 15.3). Human activities such as fossil fuel burning, industrial activities, animal husbandry, and fertilized and irrigated agriculture contribute to these increases.As concentrations of these gases rise, more of the longwave radiation emitted by Earth is trapped by the atmosphere, enhancing the greenhouse effect and causing the surface temperature of Earth to increase. The globally averaged energy budget outlined above gives us a sense of the critical factors controlling the global climate system. Regional climates, however, reflect spatial Energy (W m-2) Solar incoming radiation Terrestrial outgoing radiation 0 5 10 15 20 25 Visible region Wavelength (µm) Absorptivity 0 0 0 0 0 0 0 1 1 1 1 1 1 CH4 N2O O2 and O3 H2O 5 10 15 20 25 CO2 Atmosphere Figure 2.1. The spectral distribution of solar and terrestrial radiation and the absorption spectra of the major radiatively active gases and of the total atmosphere.These spectra show that the atmosphere absorbs terrestrial radiation more effectively than solar radiation, explaining why the atmosphere is heated from below. (Sturman and Tapper 1996, Barry and Chorley 1970.)
20 2.Earth's Climate System Space sohcoai8o diation Shortwave Longwave Convectio 100 102 by Atmosphere 14 Net lon Earth (102%)and latent plus sensible heat flux(30%)are per f the energ ongwave surface (95%).At th phere the incomins solar radiation ( m)is balanced by reflected shortwave radiation balanced by outgoing longwave radiation (114%) andenble heat flux (30raede Sturman and lapper 1990,Bacd variability in energy exchange transport by the ere an more oroug anding o t igaltheedais.Is and the fate consequences for the sing ofe ded t ad and oceanic chem
20 2. Earth’s Climate System variability in energy exchange and in heat transport by the atmosphere and oceans. Earth experiences greater heating at the equator than at the poles, and it rotates on a tilted axis. Its continents are spread unevenly over the surface, and its atmospheric and oceanic chemistry and physics are dynamic and spatially variable. A more thorough understanding of the atmosphere and oceans is therefore needed to understand the fate and processing of energy and its consequences for the ecosystems of the planet. Atmosphere Earth Space Outgoing radiation Shortwave Incoming solar radiation Absorption by H2O, dust, O3 Absorption by clouds Absorption of direct solar radiation Absorption of diffuse sky and cloud radiation Reflected by surface Backscatter by clouds Backscatter by air Net absorption by clouds, CO2,O3 Emission by H2O, CO2, O3 Emission by clouds Convective mixing Longwave Convection Latent heat flux Sensible heat flux Net longwave reradiation 100 17 3 7 16 23 114 102 12 95 7 23 69 9 48 8 26 31 Figure 2.2. The average annual global energy balance for the Earth–atmosphere system. The numbers are percentages of the energy received as incoming solar radiation. At the top of the atmosphere, the incoming solar radiation (100% or 342 W m-2 ) is balanced by reflected shortwave radiation (31%) and emitted longwave radiation (69%). Within the atmosphere, the absorbed shortwave radiation (20%) and absorbed longwave radiation (102%) and latent plus sensible heat flux (30%) are balanced by longwave emission to space (57%) and longwave emission to Earth’s surface (95%). At Earth’s surface the incoming shortwave radiation (49%) and incoming longwave radiation (95%) are balanced by outgoing longwave radiation (114%) and latent plus sensible heat flux (30%) (Graedel and Crutzen 1995, Sturman and Tapper 1996, Baede et al. 2001)
The Atmospheric System 21 The Atmospheric System reactive and have residence times of days to months Reactive species occu Atmospheric Composition amount ma e up les n0.001 and Chemistry h The chemical composition of the atmosphere vity,th are quite variable f th determines its role in Earth's energy budget. Think of the atmosphere as a giant reaction fask,containing thousands of different chemi- tainability of ecological systems(Graedel and cal compounds in gas and particulate forms, Crutzen 1995) undergoing slow and fast reactions,dissolutions Some atmospheric gases are critical for life. th thes reactions contro Photosynthetic organisms use CO,in the pres e atm of its phy ence of light to produce organic matter that eventually becomes the basic food source for all ma mical mo stribution rucial for animals and microbes (see Chapters 5 to 7) ergy Most organisms also require oxygen for meta bolic respiration.Dinitrogen (N2)makes up More than 99.9%by volume of Earth's 78%of the atmosphere.It is unavailable to ed of nitrogen.oxve and argon.Carbon dioxide.the next most abun- most organis convert it to bi ogically avar dant gas accounts for only 00367%of the y atmosnhere (Table 2 1)These percentages are pro ins (see quite constant around the world and up to CH O).nitri oxide(NO).N.( 80km in height above the surface.That homo- an geneity refects the fact that the have and i e ar long mean residence time (MRTs)in the nlant me like t MRT alculated as the total pheric ozone().are produced in the atr out of the nhere as products of chemical react time perr 1060 involving both hio enic (hiologi ically produced) th and anthropogenic gases and can.at high In concentrations.damage plants.microbes and nly ab humans the atr The atmosphere also contains aerosols which are small particles evan horizontal suspended in air nd transport of water vapor.Some of the most Some aeroso cles arise from owing dust and sea salt important radiatively active gases,such as CO, gas N2O.CH.and CFCs,react relatively slowly in and biom the atmosphere and have residence times of years to decades.Other gases are much more are ate e gase which TABLE 2.1.Maior chemical constituents of the to form cloud droplets atmosphere. Together with gases and clo erosols deter Compound Formula Concentration(%) mine the reflectivity (albedo)of the atm Nitrogen N 78.084 phere and therefore exert maior control over Oxyge the energy budget of the atmosphere.The scat- tering (reflection)of incoming shortwave 0.037 radiation by aerosols reduces the radiation Data from Schlesinger(1997)and Prentice et al(2001). reaching Earth's surface,which tends to cool
The Atmospheric System 21 The Atmospheric System Atmospheric Composition and Chemistry The chemical composition of the atmosphere determines its role in Earth’s energy budget. Think of the atmosphere as a giant reaction flask, containing thousands of different chemical compounds in gas and particulate forms, undergoing slow and fast reactions, dissolutions and precipitations. These reactions control the composition of the atmosphere and many of its physical processes, such as cloud formation. These physical processes, in turn, generate dynamical motions crucial for energy redistribution. More than 99.9% by volume of Earth’s atmosphere is composed of nitrogen, oxygen, and argon. Carbon dioxide, the next most abundant gas, accounts for only 0.0367% of the atmosphere (Table 2.1). These percentages are quite constant around the world and up to 80 km in height above the surface. That homogeneity reflects the fact that these gases have long mean residence times (MRTs) in the atmosphere. MRT is calculated as the total mass divided by the flux into or out of the atmosphere over a given time period. Nitrogen has an MRT of 13 million years; O2, 10,000 years; and CO2, 4 years. In contrast, the MRT for water vapor is only about 10 days, so its concentration in the atmosphere is highly variable, depending on regional variations in surface evaporation, precipitation, and horizontal transport of water vapor. Some of the most important radiatively active gases, such as CO2, N2O, CH4, and CFCs, react relatively slowly in the atmosphere and have residence times of years to decades. Other gases are much more reactive and have residence times of days to months. Reactive species occur in trace amounts and make up less than 0.001% of the volume of the atmosphere. Because of their great reactivity, they are quite variable in time and place. Some of the consequences of reactions among these trace species, such as smog, acid rain, and ozone depletion, threaten the sustainability of ecological systems (Graedel and Crutzen 1995). Some atmospheric gases are critical for life. Photosynthetic organisms use CO2 in the presence of light to produce organic matter that eventually becomes the basic food source for all animals and microbes (see Chapters 5 to 7). Most organisms also require oxygen for metabolic respiration. Dinitrogen (N2) makes up 78% of the atmosphere. It is unavailable to most organisms, but nitrogen-fixing bacteria convert it to biologically available nitrogen that is ultimately used by all organisms in building proteins (see Chapter 8). Other gases, such as carbon monoxide (CO), nitric oxide (NO), N2O, CH4, and volatile organic carbon compounds like terpenes and isoprene, are the products of plant and microbial activity. Some, like tropospheric ozone (O3), are produced in the atmosphere as products of chemical reactions involving both biogenic (biologically produced) and anthropogenic gases and can, at high concentrations, damage plants, microbes, and humans. The atmosphere also contains aerosols, which are small particles suspended in air. Some aerosol particles arise from volcanic eruptions and from blowing dust and sea salt. Others are produced by reactions with gases from pollution sources and biomass burning. Some aerosols are hydroscopic—that is, they have an affinity for water. Aerosols are involved in reactions with gases and act as cloud condensation nuclei around which water vapor condenses to form cloud droplets. Together with gases and clouds, aerosols determine the reflectivity (albedo) of the atmosphere and therefore exert major control over the energy budget of the atmosphere. The scattering (reflection) of incoming shortwave radiation by aerosols reduces the radiation reaching Earth’s surface, which tends to cool Table 2.1. Major chemical constituents of the atmosphere. Compound Formula Concentration (%) Nitrogen N2 78.084 Oxygen O2 20.946 Argon Ar 0.934 Carbon dioxide CO2 0.037 Data from Schlesinger (1997) and Prentice et al. (2001)