Changing Earth

G lobal change is the most fundamentalchallenge facing humanity today. As we

begin to understand more about the Earthas a system, it is clear that human activity ishaving a profound and negative impact on ourenvironment. For example, our understandingof carbon dioxide as a greenhouse gas and thestrong link between atmospheric carbon dioxideconcentrations and temperature both point tohuman activity leading to a warmer world,unlike anything seen over the last million years.A better knowledge of the Earth System and ofthe effect of increasing human activity iscrucially important for managing our environ-ment and our ability to derive sustainablebenefit.

IntroductionSince observing the Earth from spacebecame possible more than 40 years ago,satellite missions have become central tomonitoring and learning about how theEarth works. When ESA established itsLiving Planet Programme in the mid-1990s, a new approach to satelliteobservations for Earth science began,with focused missions defined,developed and operated in closecooperation with the scientific commun-

Volker Liebig, Einar-Arne Herland & Stephen Briggs Directorate of Earth Observation Programmes

Hartmut GrasslChairman of the Earth Science AdvisoryCommittee

esa bulletin 129 - february 2007 9

The Changing Earth

New ScientificChallenges for ESA’s

Living PlanetProgramme

Liebig 2/6/07 11:09 AM Page 8

Changing Earth

G lobal change is the most fundamentalchallenge facing humanity today. As we

begin to understand more about the Earthas a system, it is clear that human activity ishaving a profound and negative impact on ourenvironment. For example, our understandingof carbon dioxide as a greenhouse gas and thestrong link between atmospheric carbon dioxideconcentrations and temperature both point tohuman activity leading to a warmer world,unlike anything seen over the last million years.A better knowledge of the Earth System and ofthe effect of increasing human activity iscrucially important for managing our environ-ment and our ability to derive sustainablebenefit.

IntroductionSince observing the Earth from spacebecame possible more than 40 years ago,satellite missions have become central tomonitoring and learning about how theEarth works. When ESA established itsLiving Planet Programme in the mid-1990s, a new approach to satelliteobservations for Earth science began,with focused missions defined,developed and operated in closecooperation with the scientific commun-

Volker Liebig, Einar-Arne Herland & Stephen Briggs Directorate of Earth Observation Programmes

Hartmut GrasslChairman of the Earth Science AdvisoryCommittee

esa bulletin 129 - february 2007 9

The Changing Earth

New ScientificChallenges for ESA’s

Living PlanetProgramme

Liebig 2/6/07 11:09 AM Page 8

ity. A comprehensive strategy wasformulated for implementing theProgramme, which has resulted in theselection of six Earth Explorer missionscovering a broad range of science issues.Six candidates for the seventh missionhave been identified. At the same time,significant advances have been made inEarth science using data products andservices from the Agency’s ERS andEnvisat satellites.

At the Ministerial Council meeting inBerlin in December 2005, ESA MemberStates reconfirmed their commitment tothe concept of the Living PlanetProgramme by funding the third phasecovering the period 2008–2012. Inaddition, they approved the initiation ofthe space component of the GlobalMonitoring for Environment andSecurity (GMES), in close cooperationwith the European Commission.Although this programme is designed toprovide data that underpin operationalservices, it will also contribute signifi-cantly to Earth science, in particularthrough the collection of long time seriesof observations. In turn, the EarthExplorers will provide new understandingthat paves the way for new operationalservices. In this sense, the Living PlanetProgramme comprises complementaryelements of research and operations. This

user communities, in close cooperationwith our international partners.

Underpinning the new strategy is a setof ambitious objectives, which includes:

– launching a steady flow of missionsaddressing key issues in Earth science;

– providing an infrastructure to allowsatellite data to be quickly andefficiently exploited in areas ofresearch and applications;

– providing a unique contribution toglobal Earth observation capabilities,complementing satellites operated byother agencies and in situ observingsystems;

– providing an efficient and cost-effective process for rapidly transla-ting science priorities into spacemissions, adequately resourced withassociated ground support;

– developing innovative approaches toinstrumentation.

The overall vision for ESA’s Earthobservation activities is to play a centralrole in developing the global capabilityto understand our planet, predictchanges and mitigate the negative effectsof global change on its population.

The Challenges of a Changing WorldRecords show that the Earth has alwaysundergone major changes. Change is anatural property of the Earth System,but there is mounting evidence thatthose imposed on the system during thelast 150 years cannot be compared withany previous changes. In the lastcentury, mankind has driven thegreenhouse-gas concentrations farbeyond the maxima reached during thelast million years. It has becomeresponsible for 70% of the nitrogen and95% of the phosphorus cycle on Earth,and has reduced tropical forest areas by50%. To determine whether thesehuman-induced recent changes couldultimately destabilise the Earth System,both natural system variability and theconsequences of human activities haveto be fully understood and quantified.This is the scientific basis required forthe sustainable future management ofthe Earth System as a whole.

While the large-scale processes ofglobal change are increasingly stressingthe biosphere, other less wholesalechanges may have equally seriousconsequences for the viability ofecosystems. The loss and fragmentation

of habitat, forest degradation and lossof wetlands all remove ecological nichesoccupied by species. Over-exploitationof the natural world, as by over-fishingand over-grazing, will lead to loss ofrenewable resources and biodiversity.Still more stress, and even a healthhazard, is placed on populations bywater and air pollution, either throughcatastrophic events such as oil-spills andexplosions at chemical plants, or moreinsidious effects from the long-term useof insecticides, run-off of nitrogen-based fertilisers and air pollution inmetropolitan areas. In addition to thesethreats to the natural world, managedsystems are also subject to processessuch as loss of fertility, desertification,water stress and erosion.

Two issues are at stake here. The firstis sustainability. Human life drawsheavily on resources provided by theliving world: clean air, fresh water, food,clothing and building materials. In theinterest of future generations, we have tofind ways to guarantee that thefunctioning of the life-support systemand the ability of the ecosystems todeliver goods and services aremaintained.

Earth Observation

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1110

Changing Earth

The strategy report is available as ESA publication SP-1304 In 2005 a committee of six external scientists and six EarthScience Advisory Committee members undertook a thoroughreview of the scientific value of ESA’s Earth Observation EnvelopeProgramme. The review report was overall extremely positive inevaluating the science output of the Programme and contained11 recommendations to the Agency. These are all beingimplemented

Selected aspects of global change (atmospheric composition, land cover, temperature, biodiversity, nitrogen fixation and human population) based on information compiled by the International Geosphere-Biosphere Programme

The ESA SP-1304 report emphasises thedifferent components

synergy has long been demonstrated bythe development and scientific exploit-ation of meteorological satellites, whichcontinue to be an important part of theLiving Planet Programme.

Recent developments and advancesalready made in the Earth sciences have

emphasised the need for an updatedscience strategy. The recent Stern report( h t t p : / / w w w. h m - t r e a s u r y. gov. u k /independent_reviews/stern_review_economics_climate_change/stern_review_report.cfm)assesses the impact of climate change onthe global economy and concludes thatwhile ‘business as usual’ might have veryhigh costs, preventive measuresimplemented from today would have arelatively minor impact on the economy.Another recent study, on the socio-economic benefits of GMES, performedby Pricewaterhouse Coopers, concludedthat the benefits of GMES arepotentially very large, but they requirepolitical will in order to be efficientlyimplemented.

The updating of the strategy wasrecently undertaken under the guidanceof the Agency’s Earth Science AdvisoryCommittee and in wide consultationwith the scientific community.

Looking to the future, the newstrategy aims to assess the mostimportant Earth science questions to beaddressed in the years to come. Itoutlines the observational challengesthat these raise, and the contributionthat the Agency can make through theprogramme. These challenges will guideESA’s efforts in providing essentialEarth observation information to the

Liebig 2/6/07 11:09 AM Page 10

ity. A comprehensive strategy wasformulated for implementing theProgramme, which has resulted in theselection of six Earth Explorer missionscovering a broad range of science issues.Six candidates for the seventh missionhave been identified. At the same time,significant advances have been made inEarth science using data products andservices from the Agency’s ERS andEnvisat satellites.

At the Ministerial Council meeting inBerlin in December 2005, ESA MemberStates reconfirmed their commitment tothe concept of the Living PlanetProgramme by funding the third phasecovering the period 2008–2012. Inaddition, they approved the initiation ofthe space component of the GlobalMonitoring for Environment andSecurity (GMES), in close cooperationwith the European Commission.Although this programme is designed toprovide data that underpin operationalservices, it will also contribute signifi-cantly to Earth science, in particularthrough the collection of long time seriesof observations. In turn, the EarthExplorers will provide new understandingthat paves the way for new operationalservices. In this sense, the Living PlanetProgramme comprises complementaryelements of research and operations. This

user communities, in close cooperationwith our international partners.

Underpinning the new strategy is a setof ambitious objectives, which includes:

– launching a steady flow of missionsaddressing key issues in Earth science;

– providing an infrastructure to allowsatellite data to be quickly andefficiently exploited in areas ofresearch and applications;

– providing a unique contribution toglobal Earth observation capabilities,complementing satellites operated byother agencies and in situ observingsystems;

– providing an efficient and cost-effective process for rapidly transla-ting science priorities into spacemissions, adequately resourced withassociated ground support;

– developing innovative approaches toinstrumentation.

The overall vision for ESA’s Earthobservation activities is to play a centralrole in developing the global capabilityto understand our planet, predictchanges and mitigate the negative effectsof global change on its population.

The Challenges of a Changing WorldRecords show that the Earth has alwaysundergone major changes. Change is anatural property of the Earth System,but there is mounting evidence thatthose imposed on the system during thelast 150 years cannot be compared withany previous changes. In the lastcentury, mankind has driven thegreenhouse-gas concentrations farbeyond the maxima reached during thelast million years. It has becomeresponsible for 70% of the nitrogen and95% of the phosphorus cycle on Earth,and has reduced tropical forest areas by50%. To determine whether thesehuman-induced recent changes couldultimately destabilise the Earth System,both natural system variability and theconsequences of human activities haveto be fully understood and quantified.This is the scientific basis required forthe sustainable future management ofthe Earth System as a whole.

While the large-scale processes ofglobal change are increasingly stressingthe biosphere, other less wholesalechanges may have equally seriousconsequences for the viability ofecosystems. The loss and fragmentation

of habitat, forest degradation and lossof wetlands all remove ecological nichesoccupied by species. Over-exploitationof the natural world, as by over-fishingand over-grazing, will lead to loss ofrenewable resources and biodiversity.Still more stress, and even a healthhazard, is placed on populations bywater and air pollution, either throughcatastrophic events such as oil-spills andexplosions at chemical plants, or moreinsidious effects from the long-term useof insecticides, run-off of nitrogen-based fertilisers and air pollution inmetropolitan areas. In addition to thesethreats to the natural world, managedsystems are also subject to processessuch as loss of fertility, desertification,water stress and erosion.

Two issues are at stake here. The firstis sustainability. Human life drawsheavily on resources provided by theliving world: clean air, fresh water, food,clothing and building materials. In theinterest of future generations, we have tofind ways to guarantee that thefunctioning of the life-support systemand the ability of the ecosystems todeliver goods and services aremaintained.

Earth Observation

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1110

Changing Earth

The strategy report is available as ESA publication SP-1304 In 2005 a committee of six external scientists and six EarthScience Advisory Committee members undertook a thoroughreview of the scientific value of ESA’s Earth Observation EnvelopeProgramme. The review report was overall extremely positive inevaluating the science output of the Programme and contained11 recommendations to the Agency. These are all beingimplemented

Selected aspects of global change (atmospheric composition, land cover, temperature, biodiversity, nitrogen fixation and human population) based on information compiled by the International Geosphere-Biosphere Programme

The ESA SP-1304 report emphasises thedifferent components

synergy has long been demonstrated bythe development and scientific exploit-ation of meteorological satellites, whichcontinue to be an important part of theLiving Planet Programme.

Recent developments and advancesalready made in the Earth sciences have

emphasised the need for an updatedscience strategy. The recent Stern report( h t t p : / / w w w. h m - t r e a s u r y. gov. u k /independent_reviews/stern_review_economics_climate_change/stern_review_report.cfm)assesses the impact of climate change onthe global economy and concludes thatwhile ‘business as usual’ might have veryhigh costs, preventive measuresimplemented from today would have arelatively minor impact on the economy.Another recent study, on the socio-economic benefits of GMES, performedby Pricewaterhouse Coopers, concludedthat the benefits of GMES arepotentially very large, but they requirepolitical will in order to be efficientlyimplemented.

The updating of the strategy wasrecently undertaken under the guidanceof the Agency’s Earth Science AdvisoryCommittee and in wide consultationwith the scientific community.

Looking to the future, the newstrategy aims to assess the mostimportant Earth science questions to beaddressed in the years to come. Itoutlines the observational challengesthat these raise, and the contributionthat the Agency can make through theprogramme. These challenges will guideESA’s efforts in providing essentialEarth observation information to the

Liebig 2/6/07 11:09 AM Page 10

The second is biodiversity. On ourown planet, we are pursuing a coursethat is reducing the richness of life, anddiminishing the world that we will handon to future generations. The fact thatlife on Earth has existed continuouslyfor several billion years is due to itsdiversity. It is very likely that in thecourse of the present reduction ofbiodiversity, the Earth System’sextraordinary stability in the face ofexternal forcing is also being reduced.

Global variations in the Earth Systemdisplay very large regional differences.The human inputs to the system alsoshow widely different patterns of changeacross the globe, be it deforestation,manipulation of hydrological resources,occurrence of fires, fossil-fuel burningor land-use management. What seemsclear is that these highly variable localand regional types of environmentalmanagement sum together to produceglobal changes with major influences onthe Earth System. We are only justbeginning to understand the relatedfeedbacks and consequences for theEarth as a living planet, with humanityas one of its life-forms. Measurementsof the Earth’s properties provided bysatellites are critical in providing accessto many of the key elements of theEarth System.

The Rationale of Earth System ScienceThe latter half of the 20th century sawthe full emergence of the concept thatthe behaviour of planet Earth can onlybe understood in terms of the couplingbetween the dynamic processes in theatmosphere, solid Earth, hydrosphere,cryosphere, biosphere and anthropo-sphere. All of these components areinterlinked by a network of forcing andfeedback mechanisms that affect theother components. Global-scale effectscan arise from regional processes, andglobal-scale behaviour can have widelydifferent regional manifestations. Inaddition, processes acting at one timescale can have consequences across awide range of longer time scales. Thisparadigm, in which the Earth is seen asa coupled set of dynamical systems,

spheric concentrations of these tracegases lie naturally within well-definedbounds.

A primary lesson learned is thatunderstanding the strongly nonlinearbehaviour of the Earth System requiresatmospheric, ocean, land, cryosphericand Earth-interior processes all to beconsidered, in addition to the externalsolar driver. The Earth needs to bethought of as a system that naturallyregulates itself through a complex webof interactions and feedbacks betweenprocesses.

At the same time as we began tounderstand better the Earth as a system,it became clear that recent humanactivities are having a profound impacton this system, pushing it into stateswith unknown consequences for theplanet and mankind. An unequivocalindicator of this is the atmospheric CO2

concentration, which, since theIndustrial Revolution and the mass useof fossil fuels, has risen far beyond itsnatural limits. Our understanding ofCO2 as a greenhouse gas, and the stronglink between its concentration andtemperature, both point to humanactivity leading to a warming world,unlike anything seen over at least the lastmillion years.

constitutes the scientific disciplineknown as ‘Earth System Science’.

Major progress in many Earth sciencedisciplines has revealed that traditionallyseparated disciplines, such as oceano-graphy and atmospheric dynamics, are infact intimately connected on a range oftime and spatial scales. For example, theirregular El Niño Southern Oscillation(ENSO) shows strong coupling ofatmospheric and oceanic processes,which are in turn strongly connected to

Our perception of the Earth as asystem finds its scientific expression in amodelling spectrum running from theconceptual to the highly computational.These models encapsulate our under-standing of the Earth’s processes, theirdynamic behaviour, their relations andtheir feedbacks. Quantitative models, bytheir very nature, consist of equationswhose solution requires input data, and

the spatial patterns and overall mean ofglobal vegetation productivity.Spectacular new evidence from Antarcticice cores has shown that, over long timescales driven by orbital fluctuations, theEarth’s mean atmospheric temperature isintimately connected to the atmosphericcomposition, notably the greenhousegases carbon dioxide (CO2), methane(CH4) and nitrous oxide (N2O). It is verystriking that over at least six periods ofabout 100 000 years duration the atmo-

Earth Observation

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1312

Changing Earth

Information that can be acquired from space relevant to Solid Earth and Earth System Science

The mean tropospheric nitrogen dioxide content for 2003 as measured by Envisat’s SCIAMACHY instrument. Hot spots are theindustrialised areas of Europe, China, the USA and South Africa. Many mega-cities elsewhere can also be identified as localised spotswith enhanced concentrations. (KNMI/BIRA-IASB/ESA)

Envisat SCIAMACHY measurements of column-averaged methane volume mixing ratio (VMR), in parts per billion, averaged over theperiod August – November 2003 on a 1 x 1º horizontal grid. At least five (and up to 150) measurements are taken for each grid cell.Only a few observations are available over the ocean, since low ocean reflectivity substantially reduces the retrieval quality.Occasionally, Sun-glint or clouds at low altitudes do allow measurements over the ocean. (University of Heidelberg/ESA)

Strike probability of Typhoon Matsa, starting from the European Centre for Medium-range Weather Forecasts ECMWF) analysis of4 August 2005 00:00 UT. The ECMWF operates an ‘Ensemble Plotting System’ in which, in addition to the operational high-resolutionforecast, alternative forecasts are made at a lower resolution. (ECMWF)

evaluating the models also requires data.Hence our total knowledge about thesystem is contained in our models, ourmeasurements and how we put themtogether. Improved understanding ofhow to represent the dynamics of theEarth processes, together with theexplosion in computing power, hasallowed the construction of ever morepowerful computer codes capable ofsolving the coupled equations that makeup an Earth System model with a spatialresolution as high as about 10 km. Anequally influential development has beenthe explosion in the size of databases,both from models and satellite data, andthe interconnectivity of computersystems and databases. Pinning thesetogether has led to enormous advances inthe methods of model-data fusion anddata assimilation. These have been drivenprimarily by the needs of NumericalWeather Prediction, but the methods arecascading down to encompass all aspectsof the Earth System.

The Wider ContextFrom the outset, ESA’s Living PlanetProgramme had the ambition tofacilitate international cooperation anduse existing facilities and competenceswithin the ESA Member States and

Liebig 2/6/07 11:09 AM Page 12

The second is biodiversity. On ourown planet, we are pursuing a coursethat is reducing the richness of life, anddiminishing the world that we will handon to future generations. The fact thatlife on Earth has existed continuouslyfor several billion years is due to itsdiversity. It is very likely that in thecourse of the present reduction ofbiodiversity, the Earth System’sextraordinary stability in the face ofexternal forcing is also being reduced.

Global variations in the Earth Systemdisplay very large regional differences.The human inputs to the system alsoshow widely different patterns of changeacross the globe, be it deforestation,manipulation of hydrological resources,occurrence of fires, fossil-fuel burningor land-use management. What seemsclear is that these highly variable localand regional types of environmentalmanagement sum together to produceglobal changes with major influences onthe Earth System. We are only justbeginning to understand the relatedfeedbacks and consequences for theEarth as a living planet, with humanityas one of its life-forms. Measurementsof the Earth’s properties provided bysatellites are critical in providing accessto many of the key elements of theEarth System.

The Rationale of Earth System ScienceThe latter half of the 20th century sawthe full emergence of the concept thatthe behaviour of planet Earth can onlybe understood in terms of the couplingbetween the dynamic processes in theatmosphere, solid Earth, hydrosphere,cryosphere, biosphere and anthropo-sphere. All of these components areinterlinked by a network of forcing andfeedback mechanisms that affect theother components. Global-scale effectscan arise from regional processes, andglobal-scale behaviour can have widelydifferent regional manifestations. Inaddition, processes acting at one timescale can have consequences across awide range of longer time scales. Thisparadigm, in which the Earth is seen asa coupled set of dynamical systems,

spheric concentrations of these tracegases lie naturally within well-definedbounds.

A primary lesson learned is thatunderstanding the strongly nonlinearbehaviour of the Earth System requiresatmospheric, ocean, land, cryosphericand Earth-interior processes all to beconsidered, in addition to the externalsolar driver. The Earth needs to bethought of as a system that naturallyregulates itself through a complex webof interactions and feedbacks betweenprocesses.

At the same time as we began tounderstand better the Earth as a system,it became clear that recent humanactivities are having a profound impacton this system, pushing it into stateswith unknown consequences for theplanet and mankind. An unequivocalindicator of this is the atmospheric CO2

concentration, which, since theIndustrial Revolution and the mass useof fossil fuels, has risen far beyond itsnatural limits. Our understanding ofCO2 as a greenhouse gas, and the stronglink between its concentration andtemperature, both point to humanactivity leading to a warming world,unlike anything seen over at least the lastmillion years.

constitutes the scientific disciplineknown as ‘Earth System Science’.

Major progress in many Earth sciencedisciplines has revealed that traditionallyseparated disciplines, such as oceano-graphy and atmospheric dynamics, are infact intimately connected on a range oftime and spatial scales. For example, theirregular El Niño Southern Oscillation(ENSO) shows strong coupling ofatmospheric and oceanic processes,which are in turn strongly connected to

Our perception of the Earth as asystem finds its scientific expression in amodelling spectrum running from theconceptual to the highly computational.These models encapsulate our under-standing of the Earth’s processes, theirdynamic behaviour, their relations andtheir feedbacks. Quantitative models, bytheir very nature, consist of equationswhose solution requires input data, and

the spatial patterns and overall mean ofglobal vegetation productivity.Spectacular new evidence from Antarcticice cores has shown that, over long timescales driven by orbital fluctuations, theEarth’s mean atmospheric temperature isintimately connected to the atmosphericcomposition, notably the greenhousegases carbon dioxide (CO2), methane(CH4) and nitrous oxide (N2O). It is verystriking that over at least six periods ofabout 100 000 years duration the atmo-

Earth Observation

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1312

Changing Earth

Information that can be acquired from space relevant to Solid Earth and Earth System Science

The mean tropospheric nitrogen dioxide content for 2003 as measured by Envisat’s SCIAMACHY instrument. Hot spots are theindustrialised areas of Europe, China, the USA and South Africa. Many mega-cities elsewhere can also be identified as localised spotswith enhanced concentrations. (KNMI/BIRA-IASB/ESA)

Envisat SCIAMACHY measurements of column-averaged methane volume mixing ratio (VMR), in parts per billion, averaged over theperiod August – November 2003 on a 1 x 1º horizontal grid. At least five (and up to 150) measurements are taken for each grid cell.Only a few observations are available over the ocean, since low ocean reflectivity substantially reduces the retrieval quality.Occasionally, Sun-glint or clouds at low altitudes do allow measurements over the ocean. (University of Heidelberg/ESA)

Strike probability of Typhoon Matsa, starting from the European Centre for Medium-range Weather Forecasts ECMWF) analysis of4 August 2005 00:00 UT. The ECMWF operates an ‘Ensemble Plotting System’ in which, in addition to the operational high-resolutionforecast, alternative forecasts are made at a lower resolution. (ECMWF)

evaluating the models also requires data.Hence our total knowledge about thesystem is contained in our models, ourmeasurements and how we put themtogether. Improved understanding ofhow to represent the dynamics of theEarth processes, together with theexplosion in computing power, hasallowed the construction of ever morepowerful computer codes capable ofsolving the coupled equations that makeup an Earth System model with a spatialresolution as high as about 10 km. Anequally influential development has beenthe explosion in the size of databases,both from models and satellite data, andthe interconnectivity of computersystems and databases. Pinning thesetogether has led to enormous advances inthe methods of model-data fusion anddata assimilation. These have been drivenprimarily by the needs of NumericalWeather Prediction, but the methods arecascading down to encompass all aspectsof the Earth System.

The Wider ContextFrom the outset, ESA’s Living PlanetProgramme had the ambition tofacilitate international cooperation anduse existing facilities and competenceswithin the ESA Member States and

Liebig 2/6/07 11:09 AM Page 12

Canada. This cooperation takes severalforms, from direct cooperation on theimplementation of specific missions,through joint science activities inconnection with ESA’s and otheragencies’ missions, to interaction withinternational scientific researchprogrammes, in order to ensure thatESA’s activities have an optimum impactfrom a global point of view.

Over the years, European countrieshave developed a strong leadership inEarth System Science. The developmentof fully coupled Earth System models iswell underway at the Hadley Centre andthe University Global AtmosphericModelling Programme (UGAMP; UK),at the Max Planck Institute forMeteorology in Hamburg (D) and at theInstitut Pierre Simon Laplace andMeteo-France (F), to cite but a few.Many other European organisations areworking in the same direction. Europealso holds a strong position in other keyareas of Earth System Science, such asoceanography and glaciology. Further-more, several European organisationswith an interest in Earth Systemmodelling have grouped together withinthe European Network for Earth SystemModelling (ENES).

Earth System models are developedthrough a complex and systematicprocess of comparison with observa-tions at the relevant scale. Systematicdifferences between model simulationsand observations, called ‘biases’, pointto the incorrect representation of someprocess that must be improved in themodels, or to systematic observationalerrors that must be corrected. Once thebiases are reduced to a minimum, theremaining random differences betweenthe models and the observations can beexploited to improve further themodel’s formulation, or to create a setof model variables representing thereality at a specific point in time. Themodel can then be used for predictions.This whole process is called ‘dataassimilation’ and lies at the heart ofEarth System Science. Europe hasdeveloped a very strong leadership inpioneering the variational approach to

data assimilation. This approach wasfirst successfully developed inmeteorology, where the EuropeanCentre for Medium-Range WeatherForecasts, together with partnerEuropean meteorological centres, hasacquired an undisputed lead. Similardata-assimilation techniques are alsobeing developed in the other fields ofEarth science.

An important benefit of EarthScience satellite missions and otheractivities is the well-established potentialthey provide for developing new Earth

observation applications, the develop-ment of operational systems formeteorology being a prime example.Other areas are also progressing, andpolitical decisions like internationaltreaties on, for example, ozone andcarbon, emphasise and formalise theneed for related applications. The linkbetween science and applications worksboth ways. On the one hand, scientificprogress forms the basis for thedevelopment of new applications, butoperational systems also makeimportant contributions to scientific

Earth Observation

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Changing Earth

Key characteristics of satellitemeasurementsThey are global, enabling us to dealmeaningfully with the overall properties ofthe system, while also providingobservations of spatial heterogeneity.

They are repetitive and homogeneous,so that time-varying phenomena can bediscriminated. In many cases, long time-series are available, so that oscillationsand trends can be recognised, andsignatures of anthropogenic change canbe distinguished from natural fluctuations.

Near-simultaneous observations ofmany different variables can be made,allowing the state of the whole system tobe diagnosed, and interrelations withinthe system to be identified.

Near-realtime data delivery (within afew hours) can be ensured, whichfacilitates assimilation of satellite data intocomplex models of the behaviour of theEarth System.

The Challenges of the OceansChallenge 1: quantify the interaction

between variability in ocean dynamics,thermohaline circulation, sea level, andclimate.

Challenge 2: understand physical and bio-chemical air/sea interaction processes.

Challenge 3: understand internal wavesand the mesoscale in the ocean, itsrelevance for heat and energy transportand its influence on primary productivity.

Challenge 4: quantify marine-ecosystemvariability, and its natural and anthropo-genic physical, biological and geo-chemical forcing.

Challenge 5: understand land/oceaninteractions in terms of natural andanthropogenic forcing.

Challenge 6: provide reliable model- anddata-based assessments and predictionsof the past, present and future state ofthe oceans.

The Challenges of the AtmosphereChallenge 1: understand and quantify the

natural variability and the human-induced changes in the Earth’s climatesystem.

Challenge 2: understand, model andforecast atmospheric composition andair quality on adequate temporal andspatial scales, using ground-based andsatellite data.

Challenge 3: better quantification of thephysical processes determining the lifecycle of aerosols and their interactionwith clouds.

Challenge 4: observe, monitor and under-stand the chemistry-dynamics coupling of

the stratospheric and upper tropo-

spheric circulations, and the apparentchanges in these circulations.Challenge 5: contribute to sustainable

development through interdisciplinaryresearch on climate circulation patternsand extreme events.

The Challenges of the CryosphereChallenge 1: quantify the distribution of

sea-ice mass and freshwater equivalent,assess the sensitivity of sea ice toclimate change, and understandthermodynamic and dynamic feedbacksto the ocean and atmosphere.

Challenge 2: quantify the mass balance ofgrounded ice sheets, ice caps and glaciers, partition their relativecontributions to global eustatic sea-levelchange, and understand their futuresensitivity to climate change throughdynamic processes.

Challenge 3: understand the role of snowand glaciers in influencing the globalwater cycle and regional waterresources, identify links to theatmosphere, and assess likely futuretrends.

Challenge 4: quantify the influence of iceshelves, high-latitude river run-off andland ice melt on global thermohalinecirculation, and understand thesensitivity of each of these fresh-watersources to future climate change.

Challenge 5: quantify current changestaking place in permafrost and frozen-ground regimes, understand theirfeedback to other components of theclimate system, and evaluate theirsensitivity to future climate forcing.

The Challenges of the Land SurfaceChallenge 1: understand the role of

terrestrial ecosystems and theirinteraction with other components of theEarth System for the exchange of water,carbon and energy, including thequantification of the ecological,atmospheric, chemical and anthropogenicprocesses that control these bio-chemical luxes.

Challenge 2: understand the interactionsbetween biological diversity, climatevariability and key ecosystem character-istics and processes, such asproductivity, structure, nutrient cycling,water redistribution and vulnerability.

Challenge 3: understand the pressurecaused by anthropogenic dynamics onland surfaces (use of natural resources,and land-use and land-cover change)and their impact on the functioning ofterrestrial ecosystems.

Challenge 4: understand the effect ofland-surface status on the terrestrial

carbon cycle and its dynamics byquantifying their control and feedbackmechanisms for determining futuretrends.

The Challenges of the Solid EarthChallenge 1: identification and quantific-ation of physical signatures associatedwith volcanic and earthquake processesfrom terrestrial and space-based observ-ations.Challenge 2: improved knowledge of

physical properties and geodynamicprocesses in the deep interior, and theirrelationship to Earth-surface changes.

Challenge 3: improved understanding ofmass transport and mass distribution inthe other Earth System components,which will allow the separation of theindividual contributions and a clearerpicture of the signal due to solid-Earthprocesses.

Challenge 4: an extended understandingof core processes based on comple-mentary sources of informationand the impact of core processes onEarth System science.

Challenge 5: the role of magnetic-fieldchanges in affecting the distribution ofionised particles in the atmosphere andtheir possible effects on climate.

The Kiruna ground station, in Sweden, used for datareception and processing

Melting duration for the Greenland ice-sheet surface for theyears shown, estimated using ERS Scatterometer imagedata. The conclusion is that melting is increasing.(I. Ashcraft, Brigham Young University)

The Major Challenges for Understanding the Earth System – the Scientific Direction for ESA’s Living Planet Programme

1992

1995 1996 1997

1998 1999

0 120Days

2000

1993 1994

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Canada. This cooperation takes severalforms, from direct cooperation on theimplementation of specific missions,through joint science activities inconnection with ESA’s and otheragencies’ missions, to interaction withinternational scientific researchprogrammes, in order to ensure thatESA’s activities have an optimum impactfrom a global point of view.

Over the years, European countrieshave developed a strong leadership inEarth System Science. The developmentof fully coupled Earth System models iswell underway at the Hadley Centre andthe University Global AtmosphericModelling Programme (UGAMP; UK),at the Max Planck Institute forMeteorology in Hamburg (D) and at theInstitut Pierre Simon Laplace andMeteo-France (F), to cite but a few.Many other European organisations areworking in the same direction. Europealso holds a strong position in other keyareas of Earth System Science, such asoceanography and glaciology. Further-more, several European organisationswith an interest in Earth Systemmodelling have grouped together withinthe European Network for Earth SystemModelling (ENES).

Earth System models are developedthrough a complex and systematicprocess of comparison with observa-tions at the relevant scale. Systematicdifferences between model simulationsand observations, called ‘biases’, pointto the incorrect representation of someprocess that must be improved in themodels, or to systematic observationalerrors that must be corrected. Once thebiases are reduced to a minimum, theremaining random differences betweenthe models and the observations can beexploited to improve further themodel’s formulation, or to create a setof model variables representing thereality at a specific point in time. Themodel can then be used for predictions.This whole process is called ‘dataassimilation’ and lies at the heart ofEarth System Science. Europe hasdeveloped a very strong leadership inpioneering the variational approach to

data assimilation. This approach wasfirst successfully developed inmeteorology, where the EuropeanCentre for Medium-Range WeatherForecasts, together with partnerEuropean meteorological centres, hasacquired an undisputed lead. Similardata-assimilation techniques are alsobeing developed in the other fields ofEarth science.

An important benefit of EarthScience satellite missions and otheractivities is the well-established potentialthey provide for developing new Earth

observation applications, the develop-ment of operational systems formeteorology being a prime example.Other areas are also progressing, andpolitical decisions like internationaltreaties on, for example, ozone andcarbon, emphasise and formalise theneed for related applications. The linkbetween science and applications worksboth ways. On the one hand, scientificprogress forms the basis for thedevelopment of new applications, butoperational systems also makeimportant contributions to scientific

Earth Observation

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1514

Changing Earth

Key characteristics of satellitemeasurementsThey are global, enabling us to dealmeaningfully with the overall properties ofthe system, while also providingobservations of spatial heterogeneity.

They are repetitive and homogeneous,so that time-varying phenomena can bediscriminated. In many cases, long time-series are available, so that oscillationsand trends can be recognised, andsignatures of anthropogenic change canbe distinguished from natural fluctuations.

Near-simultaneous observations ofmany different variables can be made,allowing the state of the whole system tobe diagnosed, and interrelations withinthe system to be identified.

Near-realtime data delivery (within afew hours) can be ensured, whichfacilitates assimilation of satellite data intocomplex models of the behaviour of theEarth System.

The Challenges of the OceansChallenge 1: quantify the interaction

between variability in ocean dynamics,thermohaline circulation, sea level, andclimate.

Challenge 2: understand physical and bio-chemical air/sea interaction processes.

Challenge 3: understand internal wavesand the mesoscale in the ocean, itsrelevance for heat and energy transportand its influence on primary productivity.

Challenge 4: quantify marine-ecosystemvariability, and its natural and anthropo-genic physical, biological and geo-chemical forcing.

Challenge 5: understand land/oceaninteractions in terms of natural andanthropogenic forcing.

Challenge 6: provide reliable model- anddata-based assessments and predictionsof the past, present and future state ofthe oceans.

The Challenges of the AtmosphereChallenge 1: understand and quantify the

natural variability and the human-induced changes in the Earth’s climatesystem.

Challenge 2: understand, model andforecast atmospheric composition andair quality on adequate temporal andspatial scales, using ground-based andsatellite data.

Challenge 3: better quantification of thephysical processes determining the lifecycle of aerosols and their interactionwith clouds.

Challenge 4: observe, monitor and under-stand the chemistry-dynamics coupling of

the stratospheric and upper tropo-

spheric circulations, and the apparentchanges in these circulations.Challenge 5: contribute to sustainable

development through interdisciplinaryresearch on climate circulation patternsand extreme events.

The Challenges of the CryosphereChallenge 1: quantify the distribution of

sea-ice mass and freshwater equivalent,assess the sensitivity of sea ice toclimate change, and understandthermodynamic and dynamic feedbacksto the ocean and atmosphere.

Challenge 2: quantify the mass balance ofgrounded ice sheets, ice caps and glaciers, partition their relativecontributions to global eustatic sea-levelchange, and understand their futuresensitivity to climate change throughdynamic processes.

Challenge 3: understand the role of snowand glaciers in influencing the globalwater cycle and regional waterresources, identify links to theatmosphere, and assess likely futuretrends.

Challenge 4: quantify the influence of iceshelves, high-latitude river run-off andland ice melt on global thermohalinecirculation, and understand thesensitivity of each of these fresh-watersources to future climate change.

Challenge 5: quantify current changestaking place in permafrost and frozen-ground regimes, understand theirfeedback to other components of theclimate system, and evaluate theirsensitivity to future climate forcing.

The Challenges of the Land SurfaceChallenge 1: understand the role of

terrestrial ecosystems and theirinteraction with other components of theEarth System for the exchange of water,carbon and energy, including thequantification of the ecological,atmospheric, chemical and anthropogenicprocesses that control these bio-chemical luxes.

Challenge 2: understand the interactionsbetween biological diversity, climatevariability and key ecosystem character-istics and processes, such asproductivity, structure, nutrient cycling,water redistribution and vulnerability.

Challenge 3: understand the pressurecaused by anthropogenic dynamics onland surfaces (use of natural resources,and land-use and land-cover change)and their impact on the functioning ofterrestrial ecosystems.

Challenge 4: understand the effect ofland-surface status on the terrestrial

carbon cycle and its dynamics byquantifying their control and feedbackmechanisms for determining futuretrends.

The Challenges of the Solid EarthChallenge 1: identification and quantific-ation of physical signatures associatedwith volcanic and earthquake processesfrom terrestrial and space-based observ-ations.Challenge 2: improved knowledge of

physical properties and geodynamicprocesses in the deep interior, and theirrelationship to Earth-surface changes.

Challenge 3: improved understanding ofmass transport and mass distribution inthe other Earth System components,which will allow the separation of theindividual contributions and a clearerpicture of the signal due to solid-Earthprocesses.

Challenge 4: an extended understandingof core processes based on comple-mentary sources of informationand the impact of core processes onEarth System science.

Challenge 5: the role of magnetic-fieldchanges in affecting the distribution ofionised particles in the atmosphere andtheir possible effects on climate.

The Kiruna ground station, in Sweden, used for datareception and processing

Melting duration for the Greenland ice-sheet surface for theyears shown, estimated using ERS Scatterometer imagedata. The conclusion is that melting is increasing.(I. Ashcraft, Brigham Young University)

The Major Challenges for Understanding the Earth System – the Scientific Direction for ESA’s Living Planet Programme

1992

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1998 1999

0 120Days

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research, particularly by providing longtime-series of global data, somethingthat is notoriously difficult to justify inresearch-oriented space activities. Agood example in this respect are themissions of Eumetsat and similarorganisations.

During the last decade, the IntegratedGlobal Observing Strategy Partnership(IGOS-P) has formulated global observ-ing needs for a number of themes. Othermore recent developments are the GMESintiative by the European Union, ESAand other partners, and the Global EarthObservation System of Systems(GEOSS), to which GMES is Europe’splanned contribution. Although theseinitiatives go well beyond the scientificneeds, these are also included and theseintiatives therefore provide a natural linkbetween science and applications.

Development of specific collaborationswith major science initiatives through, forexample, the Earth Systems SciencePartnership and with international userorganisations such as the United NationsConventions, have also been a feature ofthe Programme. In all its aspects, it hasalso been a major contributor to thedevelopment of European industry in thetechnology-development, manufacturingand service sectors.

Living Planet ContributionsESA’s primary contribution to EarthScience is the provision of data productsand associated services from theAgency’s Earth observation satellites. Inaddition to data from its own satellites,ESA also facilitates the provision ofdata from other organisations’ satellites.

Earth observation satellites for Earthscience are identified, selected anddeveloped in close cooperation with thescientific community. Identification ofcandidate missions or mission conceptsis regularly conducted via open calls forproposals to the scientific community,where the newly identified challengesguide future calls. New concepts usuallyrequire a stepwise approach, wherestudies and campaigns are undertakenin order to advance the concepts. TheAgency undertakes preparatory activities

in order to ensure that the conceptsfinally selected for implementationcorrespond to the highest priority userneeds and have the broadest possiblescientific impact.

The goals of the science strategy willbe achieved only if the data gathered arevalidated and exploited thoroughly byall the research communities concerned.To achieve the envisaged scale of impactwithin the science community and insociety at large, a strong European role,innovation and commitment in the areaof data exploitation must be main-tained. Data exploitation under theLiving Planet Programme should, interms of its prime objectives, maximiseadvances and achievements in Europeanscientific understanding of the EarthSystem, develop new applications thatcan benefit society and contribute toimproved quality of life, and demon-strate new techniques and technologiesthat can strengthen European industry’scompetitiveness. Specific attentionshould be given to stimulating andfacilitating the use of Earth observationdata by research communities that donot specialise in remote sensing.

Manifested in ESA’s day-to-daycontacts with the science community,the requirements associated with Earthobservation mission operations, groundsegments, data and information hand-ling can be summarised as:

– easiest possible data access, continu-ously adapting to the latest technology;

– coherent access to many (ideally all)sources of Earth observation data andeven other geo-data;

– fast access, ideally in near-realtime;– long-term access over many (tens of)

years;– adaptation of mission, acquisition

planning and operations strategies touser demand.

Today’s users can handle and process,and therefore request, substantiallyhigher volumes of Earth observationdata than ever before. This trend isincreasing exponentially. Payload groundsegments must anticipate such an

exponential increase in the demandduring the design phase, in order to meetthe actual demand at the start ofmission operations. Modelling and long-term trend monitoring have led to alarge increase in the demand for time-series and historical data, includingregular reprocessing.

The evolution in the scientific require-ments, where the science projectsrepresent large investments both finan-cially and in terms of manpower, meansthat operations and ground segments forscientific missions now have to:

– offer the same level of reliability andoperability as former ‘operational’missions;

– additionally provide a higher degree offlexibility in adjusting and tuning theoperations schemes to new projectsand technologies, and offer a muchcloser and intelligent dialogue with theuser community.

Science today relies on a multitude ofEarth observation data sources, whichcan no longer be characterised asscience-only missions. Data from public,operational or commercial missions, aswell as non-space data, are oftenindispensable inputs to science projects.A technically simple and coherent (andfinancially affordable) access mechanismneeds to be established.

It is essential for the success of thescience strategy that the technologydevelopments, scientific investigationsand applications developments carriedout under the Programme are accom-panied by a systematic and concertedeffort to communicate the achievementsto a much wider audience, both withinEurope and beyond. This effort shouldaddress the general public, politicaldecision-makers, schools and universities,all of whom need to be made aware of,kept regularly informed about and keptinterested in Europe’s achievements inEarth observation. They must beconvinced of the tangible benefits ofinvesting public funds in this effort. e

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1716

Changing Earth

This Envisat/MERIS image of 13 December 2003 is dominated by a dust and sand storm covering theGulf of Oman. The scene includes a large part of Baluchistan, a mountainous region with some desertsand barren plains, and parts of southwestern Pakistan and southeastern Iran (top right & top centre). Itshows the dust particles (aerosols) of a continental air-mass interacting with a humid marine boundarylayer (Somali jet), leading to cloud at the edge of the outbreak. (ESA)

Envisat ASAR image of the Scott Coast, Antarctica, showing the collision of the B15Aiceberg with the Drygalski ice tongue in April 2005. (ESA)

Banda Aceh as seen by Spot-5 before (2003; left) and after (30 December 2004) the devastating Indonesian tsunami. The damaged infrastructure and areas still under water are clearly visible.(CNES/SpotImage, 2004; processing SERTIT)

Global topography and bathymetry measured by space-basedradar altimetry. (ESA, using bathymetry data courtesy of:W. Smith, NOAA Geosciences Lab., USA, D. Sandwell, ScrippsInstitute of Oceanography, USA, and altimeter-correctedelevations from P. Berry, DeMontfort Univ., UK)

Liebig 2/6/07 11:09 AM Page 16

research, particularly by providing longtime-series of global data, somethingthat is notoriously difficult to justify inresearch-oriented space activities. Agood example in this respect are themissions of Eumetsat and similarorganisations.

During the last decade, the IntegratedGlobal Observing Strategy Partnership(IGOS-P) has formulated global observ-ing needs for a number of themes. Othermore recent developments are the GMESintiative by the European Union, ESAand other partners, and the Global EarthObservation System of Systems(GEOSS), to which GMES is Europe’splanned contribution. Although theseinitiatives go well beyond the scientificneeds, these are also included and theseintiatives therefore provide a natural linkbetween science and applications.

Development of specific collaborationswith major science initiatives through, forexample, the Earth Systems SciencePartnership and with international userorganisations such as the United NationsConventions, have also been a feature ofthe Programme. In all its aspects, it hasalso been a major contributor to thedevelopment of European industry in thetechnology-development, manufacturingand service sectors.

Living Planet ContributionsESA’s primary contribution to EarthScience is the provision of data productsand associated services from theAgency’s Earth observation satellites. Inaddition to data from its own satellites,ESA also facilitates the provision ofdata from other organisations’ satellites.

Earth observation satellites for Earthscience are identified, selected anddeveloped in close cooperation with thescientific community. Identification ofcandidate missions or mission conceptsis regularly conducted via open calls forproposals to the scientific community,where the newly identified challengesguide future calls. New concepts usuallyrequire a stepwise approach, wherestudies and campaigns are undertakenin order to advance the concepts. TheAgency undertakes preparatory activities

in order to ensure that the conceptsfinally selected for implementationcorrespond to the highest priority userneeds and have the broadest possiblescientific impact.

The goals of the science strategy willbe achieved only if the data gathered arevalidated and exploited thoroughly byall the research communities concerned.To achieve the envisaged scale of impactwithin the science community and insociety at large, a strong European role,innovation and commitment in the areaof data exploitation must be main-tained. Data exploitation under theLiving Planet Programme should, interms of its prime objectives, maximiseadvances and achievements in Europeanscientific understanding of the EarthSystem, develop new applications thatcan benefit society and contribute toimproved quality of life, and demon-strate new techniques and technologiesthat can strengthen European industry’scompetitiveness. Specific attentionshould be given to stimulating andfacilitating the use of Earth observationdata by research communities that donot specialise in remote sensing.

Manifested in ESA’s day-to-daycontacts with the science community,the requirements associated with Earthobservation mission operations, groundsegments, data and information hand-ling can be summarised as:

– easiest possible data access, continu-ously adapting to the latest technology;

– coherent access to many (ideally all)sources of Earth observation data andeven other geo-data;

– fast access, ideally in near-realtime;– long-term access over many (tens of)

years;– adaptation of mission, acquisition

planning and operations strategies touser demand.

Today’s users can handle and process,and therefore request, substantiallyhigher volumes of Earth observationdata than ever before. This trend isincreasing exponentially. Payload groundsegments must anticipate such an

exponential increase in the demandduring the design phase, in order to meetthe actual demand at the start ofmission operations. Modelling and long-term trend monitoring have led to alarge increase in the demand for time-series and historical data, includingregular reprocessing.

The evolution in the scientific require-ments, where the science projectsrepresent large investments both finan-cially and in terms of manpower, meansthat operations and ground segments forscientific missions now have to:

– offer the same level of reliability andoperability as former ‘operational’missions;

– additionally provide a higher degree offlexibility in adjusting and tuning theoperations schemes to new projectsand technologies, and offer a muchcloser and intelligent dialogue with theuser community.

Science today relies on a multitude ofEarth observation data sources, whichcan no longer be characterised asscience-only missions. Data from public,operational or commercial missions, aswell as non-space data, are oftenindispensable inputs to science projects.A technically simple and coherent (andfinancially affordable) access mechanismneeds to be established.

It is essential for the success of thescience strategy that the technologydevelopments, scientific investigationsand applications developments carriedout under the Programme are accom-panied by a systematic and concertedeffort to communicate the achievementsto a much wider audience, both withinEurope and beyond. This effort shouldaddress the general public, politicaldecision-makers, schools and universities,all of whom need to be made aware of,kept regularly informed about and keptinterested in Europe’s achievements inEarth observation. They must beconvinced of the tangible benefits ofinvesting public funds in this effort. e

esa bulletin 129 - february 2007esa bulletin 129 - february 2007 www.esa.intwww.esa.int 1716

Changing Earth

This Envisat/MERIS image of 13 December 2003 is dominated by a dust and sand storm covering theGulf of Oman. The scene includes a large part of Baluchistan, a mountainous region with some desertsand barren plains, and parts of southwestern Pakistan and southeastern Iran (top right & top centre). Itshows the dust particles (aerosols) of a continental air-mass interacting with a humid marine boundarylayer (Somali jet), leading to cloud at the edge of the outbreak. (ESA)

Envisat ASAR image of the Scott Coast, Antarctica, showing the collision of the B15Aiceberg with the Drygalski ice tongue in April 2005. (ESA)

Banda Aceh as seen by Spot-5 before (2003; left) and after (30 December 2004) the devastating Indonesian tsunami. The damaged infrastructure and areas still under water are clearly visible.(CNES/SpotImage, 2004; processing SERTIT)

Global topography and bathymetry measured by space-basedradar altimetry. (ESA, using bathymetry data courtesy of:W. Smith, NOAA Geosciences Lab., USA, D. Sandwell, ScrippsInstitute of Oceanography, USA, and altimeter-correctedelevations from P. Berry, DeMontfort Univ., UK)

Liebig 2/6/07 11:09 AM Page 16