资源与生态环境（文献资料）IGBP Science 4 - Global Change and the Earth System，A planet under pressure

GLOBAL International Geosphere-Biosphere Programme IGBP Science 4 CHANGE gas gases asulphate aerosols 20194019601980 YEAR modcation generaly more uding rangelands,open owent pst penuton areas, wetands: eed by humans for millennia: rjectories of change aconnt state of flux hgenety: landscape on important as poecies responses to changes in otes and policies, with ad o-oconomicrger ovent trom remot u oted by gobz ggobel interplay and diversi Global Change and the Earth System: A planet under pressure The Global Environmental Change Programmes

IGBP Science 4 The Global Environmental Change Programmes

ForewordTheworldfacessignificantenvironmentalproblems:shortagesof cleanandaccessiblefreshwater,degradation of terrestrial and aquaticecosystems,increasesin soil erosion,loss of biodiversity,changes in the chemistry of theatmosphere,declines in fisheries,and the possibility of significant changes in climate.Thesechanges are occurring over and above the stresses imposed by the naturalvariability of adynamic planet andareintersecting with the effects of past andexistingpatterns of conflict,poverty,disease,andmalnutrition.Thechanges taking place are,infact, changes in the human-naturerelationship. They are recent, they are profound, and many are accelerating.They are cascading through the Earth's environment in ways that are difficult tounderstandand often impossible to predict.Surprises abound.At least,thesehuman-driven changes to the global environment will require societies to developa multitudeof creative responseand adaptation strategies. Some are adaptingalready;most are not.At worst,they may drivethe Earth itself into a differentstatethatmaybemuch less hospitableto humans and otherforms of life.As global environmental changeassumes amore central place in humanaffairs,science is being thrust into the unfamiliar and uncomfortable role of a majorplayer in a heated and potentially divisive international debate about the natureand severity of global change and its implications for ways of life. Much is at stakeandthegame is beingplayedhard,Despitetherisks,sciencemust accepttheresponsibilityofdeveloping and communicating the essential knowledgebasethatsocieties can use to debate, consider and ultimately decide on how to respondto global change.Thepast decade of global changeresearch,summarised in this booklet,hasunveiled more and more about the complex and interrelated nature of the EarthSystem, and about the ways in which human activities are impacting the System.Much excitingsciencehasbeen carried outandmuchhasbeenachieved.Aboveall,weknowthattheEarthSystemhasmovedwelloutsidetherangeofnaturalvariability exhibited overthe last halfmillion years at least.Thenature of changesnowoccurringsimultaneouslyintheglobal environment,theirmagnitudes andrates,are unprecedented in human history,and probably in the history of theplanet. The Earth is now operating in a no-analogue state.On the other hand, we do not yet know where critical thresholds may lie.Nor can we sayif,when andhowthe increasing human enterprisewill propel theEarth Systemtowards and across theboundaries to different states of theglobalenvironment.We also do notknow the features or operating modes of the EarthSystem that are particularly robust, which when combined with human ingenuity-with creative technological, institutional and ethical development-might lead toasafetransition to sustainability.Global change science has contributed much to anunderstandingof theEarthSystem butthereismuchto bedone.The challenge of ensuring a sustainable future is daunting and it is immediateThechallengeCANbemet, but onlywithanewand evenmorevigorous approachtoanintegrated EarthSystem science.This summary represents a small but importantsteptowards confrontingthe future,towards building an integrated Earth Systemscience and towards meeting the great challenge of global sustainability.Arild UnderdalBerrienMooreIIIPeter LemkeMichel LoreauChair, IGBPChair, IHDPChair, WCRPCo-Chair, DIVERSITAS

The world faces signifi cant environmental problems: shortages of clean and accessible freshwater, degradation of terrestrial and aquatic ecosystems, increases in soil erosion, loss of biodiversity, changes in the chemistry of the atmosphere, declines in fi sheries, and the possibility of signifi cant changes in climate. These changes are occurring over and above the stresses imposed by the natural variability of a dynamic planet and are intersecting with the effects of past and existing patterns of confl ict, poverty, disease, and malnutrition. The changes taking place are, in fact, changes in the human-nature relationship. They are recent, they are profound, and many are accelerating. They are cascading through the Earth’s environment in ways that are diffi cult to understand and often impossible to predict. Surprises abound. At least, these human-driven changes to the global environment will require societies to develop a multitude of creative response and adaptation strategies. Some are adapting already; most are not. At worst, they may drive the Earth itself into a different state that may be much less hospitable to humans and other forms of life. As global environmental change assumes a more central place in human affairs, science is being thrust into the unfamiliar and uncomfortable role of a major player in a heated and potentially divisive international debate about the nature and severity of global change and its implications for ways of life. Much is at stake and the game is being played hard. Despite the risks, science must accept the responsibility of developing and communicating the essential knowledge base that societies can use to debate, consider and ultimately decide on how to respond to global change. The past decade of global change research, summarised in this booklet, has unveiled more and more about the complex and interrelated nature of the Earth System, and about the ways in which human activities are impacting the System. Much exciting science has been carried out and much has been achieved. Above all, we know that the Earth System has moved well outside the range of natural variability exhibited over the last half million years at least. The nature of changes now occurring simultaneously in the global environment, their magnitudes and rates, are unprecedented in human history, and probably in the history of the planet. The Earth is now operating in a no-analogue state. On the other hand, we do not yet know where critical thresholds may lie. Nor can we say if, when and how the increasing human enterprise will propel the Earth System towards and across the boundaries to different states of the global environment. We also do not know the features or operating modes of the Earth System that are particularly robust, which when combined with human ingenuity - with creative technological, institutional and ethical development - might lead to a safe transition to sustainability. Global change science has contributed much to an understanding of the Earth System but there is much to be done. The challenge of ensuring a sustainable future is daunting and it is immediate. The challenge CAN be met, but only with a new and even more vigorous approach to an integrated Earth System science. This summary represents a small but important step towards confronting the future, towards building an integrated Earth System science and towards meeting the great challenge of global sustainability. Berrien Moore III Arild Underdal Peter Lemke Michel Loreau Chair, IGBP Chair, IHDP Chair, WCRP Co-Chair, DIVERSITAS Foreword

ContentsIGBPSCIENCENo.4Foreword2·ScienceHighlights4·AnIntegratedEarthSystemThe human-nature relationshipThe Earth as a systemGlobal Change7.PlanetaryMachineryRole of the biosphereTemporal variabilityLinkagesand connectivitiesAbrupt changes and critical thresholds11·TheAnthropoceneEraThe nature of global changeDrivers of changeAn Earth System perspective15·Reverberations of ChangeLong-term perspectivesCascading impactsInteracting processes and feedbacks19·LivingwithGlobal ChangeAnticipating the consequencesMultiple,interacting effectsRisks for the Earth System23·MakingEarthSystem ScienceThe dawn of a new eraQuestions at the frontierCoping with complexity and irregularityThe Earth System toolkit27TowardsGlobalSustainability?Good management of the Earth SystemAdvancing sectoral wisdomGlobal science for global sustainability30·Challenges of a changing Earth31 ·Appendix:About the Global Enviromental Change Programmes1IGBP SCIENCE No. 4

IGBP SCIENCE No. 4 1 • Foreword 2 • Science Highlights 4 • An Integrated Earth System The human-nature relationship The Earth as a system Global Change 7 • Planetary Machinery Role of the biosphere Temporal variability Linkages and connectivities Abrupt changes and critical thresholds 11 • The Anthropocene Era The nature of global change Drivers of change An Earth System perspective 15 • Reverberations of Change Long-term perspectives Cascading impacts Interacting processes and feedbacks 19 • Living with Global Change Anticipating the consequences Multiple, interacting effects Risks for the Earth System 23 • Making Earth System Science The dawn of a new era Questions at the frontier Coping with complexity and irregularity The Earth System toolkit 27 • Towards Global Sustainability? Good management of the Earth System Advancing sectoral wisdom Global science for global sustainability 30 • Challenges of a changing Earth 31 • Appendix: About the Global Enviromental Change Programmes IGBP SCIENCE No. 4 Contents

ScienceHighlightsIGBPSCIENCE No.4Somewhatmore than a decade ago it was recognised that the Earthbehavesas a system in which the oceans, atmosphere and land, and the living andnon-living parts therin, were all connected.While accepted by many, thisworkinghypothesis seldomformed the basis forglobal changeresearch.Littleunderstandingexisted of howthe Earth worked as a system,how the partswereconnected,or even abouttheimportance ofthevarious componentpartsof the system.Feedback mechanisms were not always clearly understood,norwerethedynamicscontrollingthesystemOvertheinterveningyearsmuchhasbeenlearned.Inmanyrespectsformeruncertaintiesaboutthenatureandfuturecourseofglobalchangehavebeenreduced.In others,the realisation that uncertaintyis an inherentpart of thesystemhasgainedcredence.Overthelast10yearstheunderstandingofhowhumans are bringing aboutglobal change has undergone a quantum jumpAttempts to separate natural and anthropogenicallyinduced variabilityin theEarthSystemhaveprovedtobesuccessfulinmanyrespects.Thedecadehasbeenoneof scientificchallenge.achievementandexcitementThe scientific landscapeis very different nowfrom that of the late1980sIn general,global change research has confirmed many of thehypothesesand much of the sketchy understanding of a decade ago, adding a wealth ofquantitative detail and process-level understanding at all scales.Largely througha significant increase in the ability to unravel the past,the understanding of thenatural dynamics of the Earth System has advanced greatly.It is now clear thatglobal change is one oftheparamount environmental issuesfacinghumankindatthebeginningofthenewmillennium.Thetaskof synthesisingadecadeofglobalchangeresearchhasbeendaunting, but the rewards have been great. Detailed results and individualreferencescannotbepresented here.Thesemustbesoughtfromtheindividualcore project syntheses and the IGBP-wide synthesis, soon to be publishedby SpringerVerlag intheIGBPbook series.Inthis summaryonlygeneralisedhighlights are presented, the so-called big-picture findings.They are based ondetailed,quantitativesciencethathasbeen published by a multitudeofscientistsworking worldwide over the past 1o years and longer.Major research findings:The Earth is a system that life itself helps to control. Biologicalprocesses interact strongly with physical and chemical processes tocreatethe planetary environment, but biology plays a much strongerrole than previously thought in keeping Earth's environment withinhabitable limits.Global change is much more than climate change. It is real, it ishappening nowand it is accelerating.Human activities are significantlyinfluencingthefunctioningoftheEarthSysteminmanyways;anthropogenicchanges are clearly identifiable beyond natural variability and are equal tosome of thegreat forces of naturein theirextent andimpact.IGBP SCIENCE No. 4Science Highlights

2 IGBP SCIENCE No. 4 Science Highlights Science Highlights IGBP SCIENCE No. 4 Somewhat more than a decade ago it was recognised that the Earthbehaves as a system in which the oceans, atmosphere and land, and the living and non-living parts therin, were all connected. While accepted by many, this working hypothesis seldom formed the basis for global change research. Little understanding existed of how the Earth worked as a system, how the parts were connected, or even about the importance of the various component parts of the system. Feedback mechanisms were not always clearly understood, nor were the dynamics controlling the system. Over the intervening years much has been learned. In many respects former uncertainties about the nature and future course of global change have been reduced. In others, the realisation that uncertainty is an inherent part of the system has gained credence. Over the last 10 years the understanding of how humans are bringing about global change has undergone a quantum jump. Attempts to separate natural and anthropogenically induced variability in the Earth System have proved to be successful in many respects. The decade has been one of scientifi c challenge, achievement and excitement. The scientifi c landscape is very different now from that of the late 1980s. In general, global change research has confi rmed many of the hypotheses and much of the sketchy understanding of a decade ago, adding a wealth of quantitative detail and process-level understanding at all scales. Largely through a signifi cant increase in the ability to unravel the past, the understanding of the natural dynamics of the Earth System has advanced greatly. It is now clear that global change is one of the paramount environmental issues facing humankind at the beginning of the new millennium. The task of synthesising a decade of global change research has been daunting, but the rewards have been great. Detailed results and individual references cannot be presented here. These must be sought from the individual core project syntheses and the IGBP-wide synthesis, soon to be published by Springer Verlag in the IGBP book series. In this summary only generalised highlights are presented, the so-called big-picture fi ndings. They are based on detailed, quantitative science that has been published by a multitude of scientists working worldwide over the past 10 years and longer. Major research fi ndings: • The Earth is a system that life itself helps to control. Biological processes interact strongly with physical and chemical processes to create the planetary environment, but biology plays a much stronger role than previously thought in keeping Earth’s environment within habitable limits. • Global change is much more than climate change. It is real, it is happening now and it is accelerating. Human activities are signifi cantly infl uencing the functioning of the Earth System in many ways; anthropogenic changes are clearly identifi able beyond natural variability and are equal to some of the great forces of nature in their extent and impact. 4 glacial cycles recorded in the Vostok ice core J.R. Petit et al., Nature, 399, 429–36, 1999. Age (kyr BP) inferred temperature °C ppmv CO2 ppbv CH2 280 260 240 220 200 700 600 500 400 -8 -6 -4 -2 0 2 4 400 300 200 100 350 250 150 50 0 Northern Hemisphere Average Surface Temperature 1000 1200 1400 1600 1800 2000 Year Temperature Anomaly (°C) 1.0 0.5 0.0 -0.5 -1.0 1998 Mann et al. 1999: Geo. Res. Let.,26, 6, 759 reconstruction (AD 1000-1980) raw data (AD 1902-1998) calibration period (AD 1902-1980) mean reconstruction (40 year smooothed) linear trend (AD 1000-1850) Nitrogen Year "Natural" N fixation Anthropogenic N fixation Global N fixation (Tg/yr) 150 100 50 0 1920 1940 1960 1980 2000 Human Population Billions of people 7000 5000 3000 1000 1000 8 B.C. A.D. 4 6 2 0 Species Extinctions Years Number of extinct species Mammal species Birds 60 20 0 50 40 0 1600 -1649 1650 -1699 1700 -1749 1750 -1799 1800 -1849 1850 -1899 1900 -1959 CO2 Year AD CO2 concentration (µL/L) 0 500 1000 1500 2000 350 300

Science HighlightsIGBPSCIENCENo.4The human enterprise drives multiple,interacting effects thatcascade throughthe Earth System in complex ways.Global changecannotbeunderstood interms ofa simplecause-effectparadigm.Cascadingeffects of human activities interact witheach other and with local-andregional-scale changes in multidimensional ways.The Earth's dynamics are characterised by critical thresholdsand abrupt changes. Human activities could inadvertently triggerchanges with catastrophic consequences for the Earth System.Indeed,itappearsthat sucha changewas narrowlyavoided inthecaseofdepletion of the stratospheric ozonelayer.TheEarth System has operatedin different quasi-stable states, with abrupt changes occurring betweenthem overthelasthalf millionyears.Human activitiesclearlyhavetheApotential to switch theEarth System to alternative modes of operationthatmayproveirreversible.4oThe Earth is currently operating in a no-analogue state. In terms ofkey environmental parameters,the Earth System has recentlymoved welloutsidetherangeofthenaturalvariabilityexhibitedoveratleastthelasthalfmillion years.Thenature of changesnow occurringsimultaneouslyin theEarth System,their magnitudes and rates of cbange areunprecedentedThese scientific results lead directly to two important conclusions, one forthenatureofthesocietalresponserequiredtoaddressglobalenvironmentalchange andthe otherforthetypeof science neededto understandtheEarth System.Ethics of global stewardship and strategies for Earth Systemmanagement are urgently needed. The inadvertent anthropogenictransformationoftheplanetaryenvironmentis,ineffect,alreadyaformofmanagement, or rather mismanagement.It is not sustainable.Therefore,thebusiness-as-usual way ofdealingwiththe Earthhastobereplaced-as soonas possible -by deliberate strategies of good management.A novel system of global environmental science is emerging. The0largely independent efforts of various international research programmes andnumerous national projects create thebasisfor an Earth System sciencethatis capable of tackling thecognitivetasks suggested by the research findingsatabove.Thisnewsciencewill employinnovativeintegrationmethodologiesorganize itself intoa global system with transnational infrastructures, andembark on a continuing dialoguewith stakeholders around theworld3Science HighlightsIGBP SCIENCE No. 4

Science Highlights IGBP SCIENCE No. 4 3 IGBP SCIENCE No. 4 Science Highlights • The human enterprise drives multiple, interacting effects that cascade through the Earth System in complex ways. Global change cannot be understood in terms of a simple cause-effect paradigm. Cascading effects of human activities interact with each other and with local- and regional-scale changes in multidimensional ways. • The Earth’s dynamics are characterised by critical thresholds and abrupt changes. Human activities could inadvertently trigger changes with catastrophic consequences for the Earth System. Indeed, it appears that such a change was narrowly avoided in the case of depletion of the stratospheric ozone layer. The Earth System has operated in different quasi-stable states, with abrupt changes occurring between them over the last half million years. Human activities clearly have the potential to switch the Earth System to alternative modes of operation that may prove irreversible. • The Earth is currently operating in a no-analogue state. In terms of key environmental parameters, the Earth System has recently moved well outside the range of the natural variability exhibited over at least the last half million years. The nature of changes now occurring simultaneously in the Earth System, their magnitudes and rates of change are unprecedented. These scientifi c results lead directly to two important conclusions, one for the nature of the societal response required to address global environmental change and the other for the type of science needed to understand the Earth System. • Ethics of global stewardship and strategies for Earth System management are urgently needed. The inadvertent anthropogenic transformation of the planetary environment is, in effect, already a form of management, or rather mismanagement. It is not sustainable. Therefore, the business-as-usual way of dealing with the Earth has to be replaced – as soon as possible – by deliberate strategies of good management. • A novel system of global environmental science is emerging. The largely independent efforts of various international research programmes and numerous national projects create the basis for an Earth System science that is capable of tackling the cognitive tasks suggested by the research fi ndings above. This new science will employ innovative integration methodologies, organize itself into a global system with transnational infrastructures, and embark on a continuing dialogue with stakeholders around the world. -450 -400 -350 -300 -250 -2000 -150 -100 -50 0 50 400 350 300 250 200 150 Thousands of years atmospheric C02 (ppmV) Human perturbation 1960 1970 1980 1990 2000 360 310 320 330 340 350 b) Atmospheric CO2 Concentration (ppm) Total ozone (Dobson units) Year 1950 1960 1970 1980 1990 2000 2010 300 250 200 150 100 50 0 60 90 120 150 180 -150 -120 90 120 150 180 -150 -120 50 Generated by NCAR/ACD 2001/4/9 Binned 1.0° Lon by 1.0° Lat 60 50 0 0 -12 -10 -8 0.0020 0.0024 0.0028 1/[CO2], ppmV-1 Carbon isotope ratio, % δ 13CR=-26.9‰ δ 13CR=-24.9‰ δ 13CR=-26.3‰ δ 13CR=-22.9‰ δ 13CR=-24.1‰ δ 13CR=-25.2‰ δ 13CR=-17.8‰ δ 13CR=-19.6‰

An Integrated Earth SystemOver the last two decades a newimperative has come to dominateenvironmental concerns.Witha rapidlyincreasingunderstandingofthe nature of Earth's life support system,a growing awareness hasemerged that human activities are exerting an ever acceleratinginfluence on aspects of Earth System functioning upon which thewelfare and the future of human societies depend.Thehuman-nature relationshipcomponent.Intermsofasportinganalogy,lifeisaplayer,not a spectator.Second,human activities areTHEINTERACTIONS BETWEEN ENVIRONMENTALChangEandnowsopervasiveandprofoundintheirconsequen-human societieshavealongandcomplexhistory,ces that they affect the Earth at a global scalespanning many millennia.They vary greatly throughin complex,interactive and acceleratingways;time and fromplacetoplace.Despitethese spatialhumans nowhavethe capacity to alter the Earthand temporal differences, in recent years a globalSystem in ways thatthreaten thevery processes andperspective has begun to emerge that forms thecomponents,both biotic and abiotic,upon whichframeworkforagrowingbodyofresearchwithinthehumansdependenvironmentalsciences.CrucialtotheemergenceofthisperspectivehasbeenthedawningawarenessofSystems thinkingand its application tothetwofundamental aspectsofthenatureoftheplanet.environment are not new.However,until veryThe first is that the Earth itself is a single system,recently,much of the understanding about howwithin which the biosphere is an active, essentialthe Earth operates was applied to only piecesIGBP SCIENCE No. 4An Integrated Earth System

4 IGBP SCIENCE No. 4 An Integrated Earth System Over the last two decades a new imperative has come to dominate environmental concerns. With a rapidly increasing understanding of the nature of Earth’s life support system, a growing awareness has emerged that human activities are exerting an ever accelerating infl uence on aspects of Earth System functioning upon which the welfare and the future of human societies depend. An Integrated Earth System The human-nature relationship THE INTERACTIONS BETWEEN ENVIRONMENTAL change and human societies have a long and complex history, spanning many millennia. They vary greatly through time and from place to place. Despite these spatial and temporal differences, in recent years a global perspective has begun to emerge that forms the framework for a growing body of research within the environmental sciences. Crucial to the emergence of this perspective has been the dawning awareness of two fundamental aspects of the nature of the planet. The fi rst is that the Earth itself is a single system, within which the biosphere is an active, essential component. In terms of a sporting analogy, life is a player, not a spectator. Second, human activities are now so pervasive and profound in their consequen￾ces that they affect the Earth at a global scale in complex, interactive and accelerating ways; humans now have the capacity to alter the Earth System in ways that threaten the very processes and components, both biotic and abiotic, upon which humans depend. Systems thinking and its application to the environment are not new. However, until very recently, much of the understanding about how the Earth operates was applied to only pieces

(subcomponents) of the Earth. What is really newThe Vostok ice core recordabout the understanding of the Earth System over4glacial cyclesrecorded intheVostokicecorethe last 10-15 years is a perspective that embracestheSystemasawbole.Severaldevelopmentshave蛋品服店led tothis significant change inperception:The view of Earth from a spaceship, a blue-8green sphere floating in blackness, triggersemotional feelings of a hometeeming with lifeset in a lifeless void, as well as more analytical#品perceptions of a materially limited and self-contained entity.GlobalobservationsystemsallowtheapplicationAge (kyr BP)ofconceptsthatwereonlypreviouslyapplicableJ.R.PetitetaL.Not399,429-36,1999atsubsystemlevel,orregional orlocal scales,toFigure The 420,000 year Vostok ice core record, showingthe Earth as a whole.the regular pattern of atmosphere CO, and CH,Globaldatabases allowglobal scalephenomenaconcentrationsandinferredtemperaturethroughfourtobe addressed with consistently acquired dataglacial-interglacial cycles. The upper and lower bounds ofthat have the potential for harmonization andall three variables are tightly constrained. These featurescomparison at aglobal scale.are typical of a self-regulating system.Dramaticadvances inthepowertoinfercharacAdapted from Petit et al. (1999) Nature 399,429-436 by the PAGESteristics of Earth System processes in thepast(PastGlobal Changes)International ProjectOffice.allow contemporary observationstobeviewedin a coherent time continuum.Enhancedcomputingpowermakespossiblenotonly essential data assimilation,but increasinglycarbon dioxide(CO,)and methane(CH),aresophisticatedmodels improveunderstanding oftightly coupled and show very similar patternsfunctionalinteractionsandsystemsensitivities.throughout the record.The main maxima and minima of temperatureScience has crossed the threshold of a profoundand atmospherictracegasconcentrationfollowshift in the perception of the human-environmenta regular pattern through time, each cyclerelationship,operating across humanity as a wholespanning approximately100,000 years.and at the scale of the Earth as a single systemThe range over which temperature and tracegasconcentrations varied is bounded at upper andTheEarthasasystemlowerlimits:thevaluesfallrecurrentlywithinthesame envelope through four cycles of the EarthThe fact that the Earth behaves as a single,interlinked,self-regulating system was put into dramatic focusSystem over the last half million years.in 1999withthe publicationof the420,000-yearThis systemic behaviour of Earth's environment isrecord from the Vostok ice core (Fig.1).These data,duetoa combination ofexternal forcing-primarilyarguablyamongthemostimportantproduced byvariations in solar radiation levels near the Earth'sthescientificcommunityinthe2ohcentury,providesurface-andalargeand complex arrayoffeedbacksa powerful temporal context and dramatic visualand forcings witbin Earth's environment itself.Theevidencefor an integrated planetaryenvironmentalinternal dynamics ofthe System,ratherthan externalsystem.forcings,undoubtedlykeep theplanethabitableTheVostok ice coredatagiveawealthofinsightsfor life.For example, without the thin layer ofintotheEarthSystem.Threestrikingcharacteristicsozoneintheupperatmosphere,muchmoreharmfuldemonstrate beyond any doubt that the Earth isultraviolet radiation would penetrate to the Earth'sa system,with properties and behaviour that aresurface;and without the thin layer of heat-absorbingcharacteristic of the System as a whole.greenhouse gases in the lower atmosphere,the.The temporal dynamicsof global temperatureand oftheglobalcarboncycle,as representedbyplanet's mean surface temperature would be about33°Clower than itisnow.the atmosphericconcentration ofthetracegases5IGBP SCIENCE No. 4An Integrated Earth System

An Integrated Earth System IGBP SCIENCE No. 4 5 Figure 1 The 420,000 year Vostok ice core record, showing the regular pattern of atmosphere CO2 and CH4 concentrations and inferred temperature through four glacial-interglacial cycles. The upper and lower bounds of all three variables are tightly constrained. These features are typical of a self-regulating system. Adapted from Petit et al. (1999) Nature 399, 429-436 by the PAGES (Past Global Changes) International Project Offi ce. The Vostok ice core record 4 glacial cycles recorded in the Vostok ice core J.R. Petit et al., Nature, 399, 429–36, 1999. Age (kyr BP) inferred temperature °C ppmv CO2 ppbv CH2 280 260 240 220 200 700 600 500 400 -8 -6 -4 -2 0 2 4 400 300 200 100 350 250 150 50 0 (subcomponents) of the Earth. What is really new about the understanding of the Earth System over the last 10 - 15 years is a perspective that embraces the System as a whole. Several developments have led to this signifi cant change in perception: • The view of Earth from a spaceship, a blue￾green sphere floating in blackness, triggers emotional feelings of a home teeming with life set in a lifeless void, as well as more analytical perceptions of a materially limited and self￾contained entity. • Global observation systems allow the application of concepts that were only previously applicable at subsystem level, or regional or local scales, to the Earth as a whole. • Global databases allow global scale phenomena to be addressed with consistently acquired data that have the potential for harmonization and comparison at a global scale. • Dramatic advances in the power to infer charac￾teristics of Earth System processes in the past allow contemporary observations to be viewed in a coherent time continuum. • Enhanced computing power makes possible not only essential data assimilation, but increasingly sophisticated models improve understanding of functional interactions and system sensitivities. Science has crossed the threshold of a profound shift in the perception of the human-environment relationship, operating across humanity as a whole and at the scale of the Earth as a single system. The Earth as a system The fact that the Earth behaves as a single, interlinked, self-regulating system was put into dramatic focus in 1999 with the publication of the 420,000-year record from the Vostok ice core (Fig.1). These data, arguably among the most important produced by the scientifi c community in the 20th century, provide a powerful temporal context and dramatic visual evidence for an integrated planetary environmental system. The Vostok ice core data give a wealth of insights into the Earth System. Three striking characteristics demonstrate beyond any doubt that the Earth is a system, with properties and behaviour that are characteristic of the System as a whole. • The temporal dynamics of global temperature and of the global carbon cycle, as represented by the atmospheric concentration of the trace gases carbon dioxide (CO2 ) and methane (CH4 ), are tightly coupled and show very similar patterns throughout the record. • The main maxima and minima of temperature and atmospheric trace gas concentration follow a regular pattern through time, each cycle spanning approximately100,000 years. • The range over which temperature and trace gas concentrations varied is bounded at upper and lower limits; the values fall recurrently within the same envelope through four cycles of the Earth System over the last half million years. This systemic behaviour of Earth’s environment is due to a combination of external forcing – primarily variations in solar radiation levels near the Earth’s surface – and a large and complex array of feedbacks and forcings within Earth’s environment itself. The internal dynamics of the System, rather than external forcings, undoubtedly keep the planet habitable for life. For example, without the thin layer of ozone in the upper atmosphere, much more harmful ultraviolet radiation would penetrate to the Earth’s surface; and without the thin layer of heat-absorbing greenhouse gases in the lower atmosphere, the planet’s mean surface temperature would be about 33°C lower than it is now

The recent human influence on the carbon cycle360b)350400133403308Human perturbation350(d) o asone320W31019601970198019902000300250200150-450-400-350-300-250-2000-150-100-50050Thousands of yearsFigureAtmospheric Co,concentration from the Vostok ice core record with therecent human perturbation superimposed.Theinsetshows the observed contemporary increase in atmospheric co, concentration from the Mauna Loa (Hawai) Observatory.Sources: Petit et al. (1999) Nature 399, 429-436 and National Oceanic and Atmospheric Administration (NOAA), USAGlobal Changestrong.It is increasingly clear that the Earth Systemis being subjected to an ever-increasing diversity ofOverthepastfewdecades,evidencehasmountednew planetary-scale forces that originate in humanthat planetary-scale changes are occurring rapidly.activities,ranging from the artificial fixation ofThese are, in turn, changing the patterns of forcingsnitrogen and the emission of greenhouse gasesandfeedbacksthatcharacterisetheinternaldynamicsto the conversion and fragmentation of naturalof theEarthSystem (Figs.2.3).Keyindicators,suchvegetation and the loss of biological species.It isas the concentrations of cO,inthe atmosphere,these activities and others like them that give rise toare changing dramatically,and in many cases thethe phenomenon of global cbange.linkages of these changes to human activities areBox 1:Global change is more than climate change1000 years of climate changeTheterm Earth System refers to the suite of interactingphysical,chemical,biological and human processesthatNorthern Hemispheretransport and transform materials and energy and thusAverage Surface Temperatureprovide the conditions necessary for life on the planet.Climate refers to the aggregation of components ofweather-precipitation,temperature,cloudiness,forexample-buttheclimatesystemincludesprocessesinvolving ocean,land and seaiceinaddition to theatmosphere.TheEarthSystemencompassestheclimatesystem,and many changes in Earth Systemfunctioning200n1600800directlyinvolvechangesin climate.However,thetion (AD 1000-1980)calibration period (AD 1902-1980) mew data (AD 1902-1998)Earth System includes othercomponents and processes,reconstruction(40yearsmooothed)..lineartrend (AD1000-1850)biophysical and human,important for its functioning.Mann et al.,1999:Geo. Res. Let.,26, 6, 759Some EarthSystemchanges,naturalorhuman-driven,can have significant consequences without involving anychanges in climate.Global change should not be confusedFigure Mean annual temperature variations over the northernwith climate chanqe,itis significantlymore.hemisphere for the last 1000 years.IGBP SCIENCE No.4An Integrated EarthSystem

6 IGBP SCIENCE No. 4 An Integrated Earth System Global Change Over the past few decades, evidence has mounted that planetary-scale changes are occurring rapidly. These are, in turn, changing the patterns of forcings and feedbacks that characterise the internal dynamics of the Earth System (Figs. 2,3). Key indicators, such as the concentrations of CO2 in the atmosphere, are changing dramatically, and in many cases the linkages of these changes to human activities are Figure 2 Atmospheric CO2 concentration from the Vostok ice core record with the recent human perturbation superimposed. The inset shows the observed contemporary increase in atmospheric CO2 concentration from the Mauna Loa (Hawaii) Observatory. Sources: Petit et al. (1999) Nature 399, 429-436 and National Oceanic and Atmospheric Administration (NOAA), USA The recent human infl uence on the carbon cycle -450 -400 -350 -300 -250 -2000 -150 -100 -50 0 50 400 350 300 250 200 150 Thousands of years atmospheric C02 (ppmV) Human perturbation 1960 1970 1980 1990 2000 360 310 320 330 340 350 b) Atmospheric CO2 Concentration (ppm) Mean annual temperature variations over the northern hemisphere for the last 1000 years. 1000 years of climate change Northern Hemisphere Average Surface Temperature 1000 1200 1400 1600 1800 2000 Year Temperature Anomaly (°C) 1.0 0.5 0.0 -0.5 -1.0 1998 Mann et al. 1999: Geo. Res. Let.,26, 6, 759 reconstruction (AD 1000-1980) raw data (AD 1902-1998) calibration period (AD 1902-1980) mean reconstruction (40 year smooothed) linear trend (AD 1000-1850) Figure 3 The term Earth System refers to the suite of interacting physical, chemical, biological and human processes that transport and transform materials and energy and thus provide the conditions necessary for life on the planet. Climate refers to the aggregation of components of weather - precipitation, temperature, cloudiness, for example - but the climate system includes processes involving ocean, land and sea ice in addition to the atmosphere. The Earth System encompasses the climate system, and many changes in Earth System functioning directly involve changes in climate. However, the Earth System includes other components and processes, biophysical and human, important for its functioning. Some Earth System changes, natural or human-driven, can have signifi cant consequences without involving any changes in climate. Global change should not be confused with climate change; it is signifi cantly more. Box 1: Global change is more than climate change strong. It is increasingly clear that the Earth System is being subjected to an ever-increasing diversity of new planetary-scale forces that originate in human activities, ranging from the artificial fixation of nitrogen and the emission of greenhouse gases to the conversion and fragmentation of natural vegetation and the loss of biological species. It is these activities and others like them that give rise to the phenomenon of global change

Planetary MachineryAn understanding of the nature of the Earth System before human activitiesbecameanimportantfactorprovidesthebackdrop of naturalcyclesandof processes,patterns and variabilityagainst whichcurrentandfutureanthropogenic changes must be evaluated.Over the past decade research hasidentified manykey characteristics of the ways in which the Earth Systemoperates to keep the global environment within limits suitable for life.of the carbon fixed by phytoplankton in the upperRoleofthebiospherelayers sinks to the interior, where it is stored awayBIOLOGICALPROCESSESINTERACTSTRONGLYWithphVSiCalfromcontactwiththeatmosphereforhundredsonandchemicalprocessatetheenvironmentthousandsofyears.Thisbiologicalpump,alongwiththatkeepsEarthhabitablefor life.Themore thatnicalconstraintsonthesolubilityofthefunctioningoftheEarthSysteninedinphysico-chemcO,controlthepatternofCO,exchangebetweendetail,theeroleplavedaancnondtheatmosphere.Intriguingly,thebylifeitsHofthephytoplanktonspeciesinvolvedintheexamDle10l09antimayhold a keyto therate of andDiologito thecarbonstorage (Fig.4)otentialfotlerrestrialbiotaarealsoanimportantcomponenttiminEarthSystemfunctioninginanumberofways.Forbyphytoplanin.theexample,thetypeofvegetationpresentonthelandsurfacettherebsurface influences the amount of watertranspiredCO,todissolefromtheatm24 Planetary MachineryIGBP SCIENCE No. 4

Planetary Machinery IGBP SCIENCE No. 4 7 Role of the biosphere BIOLOGICAL PROCESSES INTERACT STRONGLY with physical and chemical processes to create the environment that keeps Earth habitable for life.The more that the functioning of the Earth System is examined in detail, the greater is the realisation of the role played by life itself in helping to control the System. For example, biological processes contribute signifi cantly to the absorption of atmospheric CO2 by the oceans, which in turn controls atmospheric CO2 concentration on long time scales. Photosynthesis by phytoplankton reduces the amount of CO2 in the surface layer of the ocean, thereby allowing more CO2 to dissolve from the atmosphere. About 25% of the carbon fi xed by phytoplankton in the upper layers sinks to the interior, where it is stored away from contact with the atmosphere for hundreds or thousands of years. This biological pump, along with physico-chemical constraints on the solubility of CO2 , control the pattern of CO2 exchange between the oceans and the atmosphere. Intriguingly, the nature of the phytoplankton species involved in the biological pump may hold a key to the rate of and potential for carbon storage (Fig. 4). Terrestrial biota are also an important component in Earth System functioning in a number of ways. For example, the type of vegetation present on the land surface infl uences the amount of water transpired An understanding of the nature of the Earth System before human activities became an important factor provides the backdrop of natural cycles and of processes, patterns and variability against which current and future anthropogenic changes must be evaluated. Over the past decade research has identifi ed many key characteristics of the ways in which the Earth System operates to keep the global environment within limits suitable for life. Planetary Machinery

continuously on all time-scales (Fig.5).A carefulWho's there mattersexamination of evidencefrom thepast shows that:variability is reflected not onlyintemperature-variabilityinthehydrologicalcvcle,whichisoften ofmuchgreaterimportancetohumanpopulations, has been quite extreme on alltime-scalesinthepast,no single variable orregion truly reflectsglobalvariability-globalmean conditions maskimmensevariationsinregionalresponses,during thelate Holocene.when the naturalforcings and boundary conditions were similartothoseoperatingtoday,thereisstrongevidencethattherangeofvariabilitysignificantlyexceededthat captured by instrumental records.RelianceFigureLife in the oceans plays an important role in maintainingon theveryshortperiod ofinstrumental recordsgeochemical balance in the Earth System and the fate ofthe carbon that is fixed by the ocean's phytoplanktongives a false sense of the true variability of theisverymuchafunctionofthesizeandtaxonomyofEarth System.the species present. For example, in addition to fixingVariability in theclimate systemcarbonviaphotosynthesis,onegroupofphytoplankton,thecoccolithophorids,suchas Emiltiania huxleyi (shownV11.0above) produces calcium carbonate platelets (liths).Each lith is only about 2.5 μm in lengthbut many0.8are produced every year. It is estimated that bloomsOON0.6of E.huxleyi cover about 1.4millionkm2of theaz.1Poceaneveryyear.Thus,overgeologicaltime,tremendousAntarctica1Oaccumulations of carbon fixed by coccolithophorids50-100150develop.The white cliffs of Dover are, for example,hofYearsRa5largely comprised of platelets from coccolithophorids.0.3Source: K.Richardson.P0.20.15back to the atmosphere and the absorption oreino.reflection of the sun's radiation.The vegetation's20rooting patterns and activity are also importantireenloncontrollersofbothcarbonandwaterstorageandof101520253035404550fluxes between the land and the atmosphere.The02biological diversity of terrestrial ecosystems affects0.16Ethe magnitude ofkey ecosystem processes such0.120.08as productivity,and plays a role in the long-termGreenland0.04stability of ecosystem functioning in the face of a12-1416changingenvironment.TemporalvariabilityVariability and change are realities of the EarthB-year changeSystem,and static,so-called equilibrium,conditions0.00are unlikely to be a part of the System on almostFigure Variability in the climate system.Ice accumulationany time scale.The notion that unusally stablerate history at four different time scales. Data fromconditions prevailed over the past several millenia,Antarctica(toppanel)andGreenland(bottomthreewhenhumancivilisationsdeveloped,andrepresentpanels).normal conditions isfalse.The record showsthatAdapted from Jacobson et al. (eds.)(2000) Earth System Science,the functioning of the Earth System has variedAcademic Press, p. 479.8IGBP SCIENCE No. 4Planetary Machinery

8 IGBP SCIENCE No. 4 Planetary Machinery Figure 4 Life in the oceans plays an important role in maintaining geochemical balance in the Earth System and the fate of the carbon that is fi xed by the ocean’s phytoplankton is very much a function of the size and taxonomy of the species present. For example, in addition to fi xing carbon via photosynthesis, one group of phytoplankton, the coccolithophorids, such as Emiliania huxleyi (shown above) produces calcium carbonate platelets (liths). Each lith is only about 2.5 µm in length but many are produced every year. It is estimated that blooms of E. huxleyi cover about 1.4 million km2 of the ocean every year. Thus, over geological time, tremendous accumulations of carbon fi xed by coccolithophorids develop. The white cliffs of Dover are, for example, largely comprised of platelets from coccolithophorids. Source: K. Richardson. Who’s there matters back to the atmosphere and the absorption or refl ection of the sun’s radiation. The vegetation’s rooting patterns and activity are also important controllers of both carbon and water storage and of fl uxes between the land and the atmosphere. The biological diversity of terrestrial ecosystems affects the magnitude of key ecosystem processes such as productivity, and plays a role in the long-term stability of ecosystem functioning in the face of a changing environment. Temporal variability Variability and change are realities of the Earth System, and static, so-called equilibrium, conditions are unlikely to be a part of the System on almost any time scale. The notion that unusally stable conditions prevailed over the past several millenia, when human civilisations developed, and represent normal conditions is false. The record shows that the functioning of the Earth System has varied continuously on all time-scales (Fig. 5). A careful examination of evidence from the past shows that: • variability is refl ected not only in temperature – variability in the hydrological cycle, which is often of much greater importance to human populations, has been quite extreme on all time-scales in the past, • no single variable or region truly refl ects global variability – global mean conditions mask immense variations in regional responses, • during the late Holocene, when the natural forcings and boundary conditions were similar to those operating today, there is strong evidence that the range of variability signifi cantly exceeded that captured by instrumental records. Reliance on the very short period of instrumental records gives a false sense of the true variability of the Earth System. Figure 5 Variability in the climate system. Ice accumulation rate history at four different time scales. Data from Antarctica (top panel) and Greenland (bottom three panels). Adapted from Jacobson et al. (eds.) (2000) Earth System Science, Academic Press, p. 479. Variability in the climate system Thousands of Years Before Present 0 150 50 100 Normalized Accumulation Rate 1.2 0.2 0.4 0.6 0.8 1.0 Antarctica Younger Dryas 0 50 5 40 10 45 15 20 25 35 30 Accumulation Rate (m/yr) 0.3 0.05 0 0.1 0.15 0.2 0.08 0.04 0.12 0.16 0.2 0.25 Greenland Greenland Greenland 0.1 0.0 0.2 0.3 10 16 12 14 3-year change