GRAND CHALLENGES IN EARTH ANDENVIRONMENTAL SCIENCE

So what are the big environmental problems, the grandchallenges of the coming decades? Here are six, characterized on a process level rather than a discipline or theme basis:

▲ Recognizing the signal within the natural variability

▲ Defining mass flux and energy balance in natural systems

▲ Identifying feedback between natural and perturbed systems

▲ Determining proxies for biodiversity and ecosystem health

▲ Quantifying consequences, impacts, and effects

▲ Effectively communicating uncertainty and relative risk

Each of these challenges will require creative attacks involvingintegration of efforts in all the disciplines mentioned above. Foran alternative view of grand challenges in environmental sciencefrom a topical perspective, see National Research Council (2001).

Recognizing the Signal Within the Natural Variability

This first challenge is, of course, at the crux of the globalwarming conundrum. Are steady increases in global temperature(and accompanying climate changes) in the past 150 yearssimply an expression of natural variability, or are they a directresult of mankind’s activities that have resulted in an increase ingreenhouse gases? The weight of the scientific evidence suggeststhe latter, however the debate on global warming has turned intoa high-stakes, international issue with potentially multibillion-dollar implications.

Documenting and understanding natural variability is a vexingtopic in almost every environmental problem: How do werecognize and understand changes in natural systems if we don’tunderstand the range of baseline levels? Our geologic perspectiveallows us to view the short interval of historical records with ahealthy skepticism. Figure 1 shows a 350 year record ofprecipitation in California (1600–1950), determined using 52 tree-ring chronologies as proxies for precipitation (Fritts, 1984). I haveadded two important historical dates to this chronology: 1769,the founding of the first of the Spanish missions in California andthe inception of written records; and 1849, the beginning of theCalifornia gold rush that within years increased the number and

2000 Presidential Address:

Grand Challenges in Earth and Environmental Sciences:Science, Stewardship, and Service for the Twenty-First CenturyMary Lou Zoback, U.S. Geological Survey, MS 977, 345 Middlefield Road, Menlo Park, CA 94025, USA

INTRODUCTIONA measure of our future success as earth scientists will dependon our ability to help our global society find and implementeffective solutions to environmental problems. In its mostinclusive sense, environmental science could be consideredto be “the” earth science. As used here, environmentalscience is defined to be a broadly integrative study ofprocesses occurring at or near the surface of Earth andinvolving interactions between the uppermost lithosphere, theatmosphere, the hydrosphere, and the biosphere (whichincludes mankind). It encompasses a broad range oftraditional disciplines including biology, ecology,meteorology, atmospheric sciences, hydrology, oceanography,geology, and geophysics.

Broad agreement exists within the scientific community thatwe must employ an integrated systems approach to solvingcomplex environmental problems. Our long-term goal forenvironmental science should be to understand natural andperturbed systems well enough to predict outcomes,consequences, and impacts.

The effects of a number of important drivers of environmentalscience must be factored into our approaches to solvingenvironmental problems: population growth, concentration ofpopulation into huge urban centers (many of which aresituated in areas subject to natural hazards), an acceleratingneed for resources, mankind as a significant agent of changein the earth system, and unrealistic expectations for absoluteguarantees from science. This final driver is a purelysociopolitical factor, but a critical one in seeking societallyacceptable solutions to environmental problems.

Rapid technological developments in information science,telecommunications, and sensor development in the past fewdecades have greatly increased our ability to tackle complexenvironmental problems. In the earth sciences, we are onlybeginning to harness the power of broad bandwidthobservational systems and real-time data delivery to probeactive natural systems and processes on spatial scales andtime scales never before possible. For example, we now havethe capability to globally monitor physical properties daily(e.g., see www.ssec.wisc.edu/data/sst.html for daily seasurface temperature maps). Fifty years ago, the concept ofhaving daily global snapshots of direct measurements of avariety of earth properties freely available on home computerswas unthinkable. These advances will enable increasinglysophisticated numerical modeling of natural systems, but inmany cases our scientific understanding of the interconnectedphysics, geology, chemistry, and biology of these naturalsystems is still at the infancy stage.

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distribution of population manyfoldthroughout the state. These two datesroughly bracket a significant 80–90 yearinterval of apparent drought relative tothe 1901–1961 average precipitationvalue. While this extended dry periodoccurred during a period of historicalrecords, it was probably not noteworthysince the mission padres had no baselineagainst which to judge the climate.Clearly, a repeat of a similar extended dryperiod in California today due to naturalvariability would be devastating to thevast agricultural enterprise that provides~50% of the vegetables, fruits, and nutsfor the entire nation (California AgricultureStatistics Service, 1999) and feeds a thirstypopulation with one of the fastest growthrates in the country.

Natural variability is important on bothspatial and temporal scales. In an attemptto establish natural geochemical back-ground baselines to monitor environ-mental change, Davenport et al. (1993)analyzed samples of organic sediment inmore than 40,000 lakes in Newfoundlandand Labrador. They concluded thatcompared to the regional background,there was no evidence of enrichment ofarsenic levels in the vicinity of the majorurban center of St. John’s. In contrast, thelead levels they measured near St. John’swere above the ninety-ninth percentile ofvalues found in all Newfoundland,including areas of lead mineralization,suggesting an anthropogenic source nearSt. John’s. The regional baseline data thusprovide the range of natural variability toassess the geochemical signals within theurban areas.

Defining Mass Flux andEnergy Balance in Natural Systems

This second challenge requires athorough quantitative understanding ofthe physics, chemistry, geology, andbiology of natural systems. Understandingbiogeochemical cycles such as the carbonor nitrogen cycle is fundamental to

understanding how larger natural systems,such as the global climate system,function. The name itself—biogeochemical cycles—implies complex,interconnected processes, which involvewater, air, soil, biological, and sometimeshuman pathways (Fig. 2).

Figure 1. Average annual precipitation in California for 1600–1950 as determined using tree-ring chronology from 52 trees as a proxy forprecipitation (Fritts, 1984). Horizontal line represents 1901–1961 average precipitation value from instrumental records.

Figure 2. Major fluxes and storage associated with carbon cycle. Image courtesy of NASAEcology Program. Fluxes and storages from Intergovernmental Panel on Climate Change,1995 Special Assessment Report on Climate Change. See www.unep.ch/ipcc/pub/sarsum1.htm.

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A practical example of a natural systemthat we have a critical need to understandis the vadose or unsaturated zone: thenear-surface zone in Earth where waterexists but does not fill interconnected porespace. As indicated in Figure 3, interactionof climate, rock properties, hydrology, andbiology through evapotranspiration areessential in producing the net upwardflux of moisture within the near surface toassure that the zone remains unsaturated.The vadose zone in fractured rock in thearid west is where we plan to store (andin fact are already inadvertently storing)high-level radioactive waste (e.g., theproposed repository at Yucca Mountain,Nevada, and the Hanford Reserve, aformer nuclear weapons facility locatedalong the Columbia River in southeasternWashington). However, quantitativeunderstanding of the myriad of criticalinterconnected atmospheric, hydrologic,geochemical, and biological processesacting on and within this zone remainselusive. As indicated by former under-secretary of energy, Ernest Moniz, in aNew York Times article on the myriad ofproblems with tanks leaking high-levelwaste at the Hanford Reserve (“AdmittingError at a Weapons Plant,” March 23, 1998),“There has not been enough science forvadose zone assessment. …The vadosezone is intellectually virgin territory.”

Moniz, a former chair of the PhysicsDepartment at the Massachusetts Instituteof Technology, recognized the need tounderstand the entire system in order tobe able to assess human impacts upon it.

A lack of understanding of this naturalsystem has led to solutions that couldexacerbate existing environmentalproblems at the Hanford Reserve, whichis currently under U.S. Department ofEnergy (DOE) control for maintenanceand cleanup. On the central plateau ofthe Hanford site, ~55 million gallons ofliquid, high-level radioactive waste isstored in 177 below-ground tanks. Thetanks, 148 of which are single walled,were filled with the waste beginning inthe 1940s. Not surprisingly, at least one-third of the tanks are believed to haveleaked, and more than one milliongallons of the liquid waste (with anestimated more than 1.8 million curies) isnow in the subsurface (National ResearchCouncil, 2000). DOE engineers initiallybelieved that the unsaturated zone wouldact as a barrier to contaminant migration,and that transit times to deep aquifersbelow the vadose zone would be on theorder of tens of thousands of years.However, large plumes of radioactive andchemical contaminants have already beendetected in the aquifer underlyingHanford and indicate transit times

through the vadose zone of somecontaminants of tens of years, not tens ofthousands of years (National ResearchCouncil, 2000).

To protect workers from possiblehazards associated with the leaking tanks,site engineers decided to cover theground surface above the tanks withgravel to prevent the spread ofcontamination by wind, rootingvegetation, and burrowing animals. Thissolution, of course, reduced the risk ofsurface contaminant transport as well asfire hazards, but may have increasedinfiltration, thereby providing a potentialdriving force to carry already leakedcontamination to the groundwater. Inaddition, by destroying the vegetation, acritical biological pathway for upwardflux of water through evapotranspirationin the vadose zone was destroyed.

Identifying FeedbackBetween Natural andPerturbed Systems

As the vadose zone exampledemonstrates, this third challenge islinked to the previous challenge butincludes the recognition that actions ofman have deliberately or inadvertentlyperturbed natural systems. A dramaticexample of such feedback affecting localurban weather has been suggested nearAtlanta, Georgia. A comparison of satelliteinfrared imagery taken over a 19 yearperiod indicates the extensive urbansprawl in the vicinity of that city over thepast two decades (Fig. 4). The imageryindicates the ground is actually hotter andemitting more heat at night even thoughevening air temperatures are cooler(Quattrochi et al., 2000). Bornstein andLin (2000) have suggested that eveningthunderstorms southwest of Atlanta arecaused by the effects of an urban heatisland created by the urban sprawl.

Probably nowhere has mankind had abigger impact than on the water cycle. Inaddition to the natural components of thiscycle, we must also understand the effectsof irrigation, flood control, pollution,reclamation, urban use, and agriculturaluse, among others. For millennia,mankind has been a victim of the watercycle. Today, while we fundamentallycontrol a great deal of the water cycle, wehave only a nascent understanding of thefull impact of our control on this system.The water cycle is, of course, just onecomponent of the global climate cycle,the one natural system for which we arefurthest along in developing complexcomputer models that incorporate notonly the significant physics and chemistry

Figure 3. Block diagram showing processes acting within proposed vadose (unsaturated) zonerepository at Yucca Mountain (Office of Civilian Radioactive Waste Management, 1998).

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of the system but also attempt to incorporatesome of the complex feedbacks induced by theactivities of man.

Identifying Proxies forBiodiversity or Ecosystem Health

Identifying geologic, chemical, or biologic parameters or asuite of parameters that can indicate the health or biodiversity ofan ecosystem represents a substantial challenge for allpractitioners of environmental science. This challenge gets at thecrux of solving environmental problems. Once we think wehave found solutions for environmental problems, how do wemonitor or measure (one hopes remotely) parameters thatindicate the effectiveness of our corrective actions or efforts atrestoration or remediation?

Some tools for remote monitoring of ecosystem health alreadyexist. A National Aeronautics and Space Administration (NASA)sensor currently being tested, the Vegetation Canopy LIDAR(light detection and ranging), or VCL tool, can measure thedensity and structure of forest vegetation (NASA, no date). Byanalyzing multiple bounces within the reflecting radar signal,this sensor is able to map the areal distribution of tree height,the vertical structure within the forest, and the subcanopy topog-raphy at very high resolution. NASA plans to launch a satellite-based VCL system to do forest biomass monitoring on a globalscale in 2003. Interestingly, geologists in the U.S. GeologicalSurvey (USGS) Earthquake Program have used LIDAR obtainedfrom aircraft to map the topography under the dense tree coverand discover young thrust fault scarps in the Seattle,Washington, region (Haugerud et al., 2001; Blakely et al., 2002).In this case, the vegetation canopy information is simply noise!

We also need to explore new types of land-based monitoringtechniques and capabilities to measure the health of natural orperturbed systems. Restoration of wetlands is an issue currentlyreceiving a great deal of political and economic attention.Ecologically, wetlands provide numerous critical functions,including: filtering sediments and chemicals from water washedthrough them, providing flood control, helping regulateatmospheric gases, and providing habitat and food that attract

and support abundant fish and wildlife (Constanza et al., 1997).The state of California alone has lost 90%–95% of its wetlandssince the middle of the nineteenth century (Natural ResourcesConservation Service, 1999; California Habitat ProtectionDivision, Wetlands, no date). Louisiana has requested federalfunding for a $14 billion plan to restore its coastal wetlands,which are disappearing at a record pace (Bourne, 2000). Howcan we monitor the progress of such a massive restorationeffort? Perhaps by deploying millions of low-cost, low-powersensors to monitor and report back in real-time criticalparameters such as temperature, humidity, salinity, and waterchemistry, which are then continuously processed and analyzed.Of course, to do useful monitoring, we need to understand thesystem being monitored. Maybe it is time for a grand experimentto make a big step forward.

Quantifying Consequences, Impacts, and Effects

This fifth challenge is directly related to the long-term goal of understanding natural systems well enough to quantify theirconsequences and impacts in response to changes in natural or anthropogenic forcings. We need to build complex computermodels of natural systems that can forecast impending disastersand predict their likely effects or can predict the consequencesof a given societal decision or the trend or change in a naturalsystem.

Figure 5 illustrates such a prediction for the change inDouglas fir growth range corresponding to a doubling in CO2

over pre-industrial levels, a level we might experience sometimethis century if current emission rates of greenhouse gasescontinue. Thompson et al. (1998) used knowledge of the factorscontrolling Douglas fir growth and the results of climatemodeling to predict a significant contraction of the range ofDouglas fir in western North America in a 2 × CO2 climate.

Figure 4. Urban heat island created by urban sprawl in vicinity of Atlanta, Georgia. A: Comparison of infrared images taken in 1973 and1992 indicating extensive growth of development in this 20 year period. B: Comparison of daytime (left) and nighttime (right) surface temperaturesaround Atlanta inferred from thermal infrared data. Images courtesy of Dale Quattrochi, Project ATLANTA (ATlanta Land use ANalysis:Temperature and Air quality), at NASA Marshall Space Flight Center. See www.ghcc.msfc.nasa.gov/urban/urban_news.html.

A

B

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For most systems, however, we will notbe able to predict absolutely, but mustforecast probabilistically. We can predictthe most likely outcome and assign alevel of certainty to that prediction—orgive a range of the most likely outcomesat a given confidence level. Probabilisticforecasting is widely applied in my ownfield, the study of earthquakes andearthquake hazards. We are currentlyunable to scientifically predictearthquakes, and even if we could, thatwould not prevent the damage tobuildings and infrastructure. A recentstudy led by the USGS in the SanFrancisco Bay area assigned a 70%likelihood of a damaging earthquake(≥6.7 M) striking the region during thenext 30 years (Working Group forNorthern California EarthquakeProbabilities, 1999). The 30 year timeframe of this forecast was selected aslarge enough to represent a significantfraction of the earthquake cycle for majorevents on any given fault (typicallyseveral hundreds of years) and shortenough to have some societal reference(e.g., the length of a typical homemortgage). The high likelihood indicatesmitigation measures might be costeffective.

This forecast gives only a likelihood ofthe occurrence of a future earthquake andnot its likely effects. The forecastinformation can be combined withtheoretical models of earthquake rupturesand seismic wave propagation to giveannual likelihoods of exceeding a givenlevel of ground motion. The USGS NationalSeismic Hazards maps (http://geohazards.cr.usgs.gov/eq/) are probabilistic maps ofannual exceedance of ground-motionlevels over different time periods.Exceedance maps are used to developand upgrade seismic design criteria in theUnified Building Codes.

Effectively CommunicatingUncertainty and RelativeRisk

Perhaps our biggest challenge as earthscientists is to refocus society’s desire forabsolute guarantees from science andreplace it with an acceptance that mostsolutions are uncertain and will carrysome level of risk and also some level ofenvironmental consequences. We mustframe the questions and explain thechoices so that decision makers can makebetter-informed decisions. Forcing onecorrect, “ultimate” solution will rarely besocially acceptable.

Safe, long-term containment of high-level radioactive waste is an excellent

example of the dilemmas faced in findingacceptable solutions to environmentalproblems. Spent nuclear fuel and otherhigh-level radioactive waste is currentlystored at 72 commercial reactors in 33U.S. states as well as at an additional 86government sites around the country(Office of Civilian Radioactive WasteManagement, 1998; Fig. 6). Many of thenuclear reactors are along coastlines or inriver valleys. Typically, the spent fuel rodsare stored in cooling ponds located at thesurface of these sites. If we don’t comeup with a long-term solution forradioactive waste storage, we are optingfor the default solution of continuedstorage at the widely dispersed sites,many of which were never designed forvery long-term storage (>100 years, 30–50years of which have already passed) andare exposed to multiple hazards.

The nation is near the end of sitecharacterization for a potential high-levelradioactive waste underground storagerepository at Yucca Mountain, Nevada.Many of the geologic, geochemical, andhydrologic processes affecting the sitehave been carefully examined andquantified. However, the long-termsuitability of this site for a geologicrepository cannot be guaranteedabsolutely; only statements about thelikelihood of migration of radioactivecontaminants away from the site and

traveling through the aquifer can bemade. The “default” solution I mentionedand the risks associated with it have notbeen factored into our public discussionand dialogue on the suitability of YuccaMountain or any other site as the nation’sgeologic repository for high-levelradioactive waste, nor have the policychoices between Yucca Mountain andcontinued existing storage been properlyframed for decision makers.

WHAT CAN WE DO TO MEET THESECHALLENGES?

We, as earth scientists, can do a greatdeal to meet these grand challenges inenvironmental science. First, we need tolearn some biology and ecology. We needto aggressively exploit technologicaladvances in the area of monitoring activeprocesses, both in situ and remotely fromspace or aircraft. We need to work withinformation technology experts todevelop the means to process hugeamounts of data generated by thesemonitoring sensors in real time andassimilate this information into self-learning complex numerical models of

Figure 5. Distribution of Douglas fir in western North America at present and anticipatedchanges in range in 2 × CO2 environment (from Thompson et al., 1998).

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natural systems that incorporate feedbackand evolve in real time.

However, finding workable solutions tolarge-scale environmental problems willrequire more than first-rate integrativephysical and biological science. Implicitin its definition, environmental sciencehas a human and social aspect.Environmental scientists must work withsocial scientists and economists to gainsocietal acceptance of proposed solutionsthat utilize the best scientific andengineering judgment, but that willundeniably be associated withconsiderable uncertainty. Solutions forenvironmental problems will represent adelicate balancing act in which societymust weigh the level of risk they arewilling to live with as well as the level ofenvironmental consequences.

WHAT SHOULD WE DO?We should begin now to design grand,

bold, process-level experiments that fullyexploit modern technology to tackle these

challenges. We should acknowledge thatsolving these problems is every bit asdifficult and complex as building theatomic bomb that started the radioactivewaste problem.

For example, we should tackle safe,long-term isolation of high-levelradioactive waste as one of the grandestscientific, technological experiments ofthe twenty-first century. Globally, our lackof solutions to this problem will continueto affect our world’s energy future. DOEis now considering a staged approach torepository design, development, andoperation that recognizes that we do notyet understand many of the importantprocesses involved. In a 1999 letter to theNational Research Council, DOErequested a study on such an option,stating that they were interested in anapproach in which “decisions must bemade in a step-wise and reversiblefashion.” This is exactly the approach thescientific community has been advocatingfor more than a decade (NationalResearch Council, 1990). We, the earthscience community, should become active

participants in such a grand experiment.The challenges I’ve outlined are

daunting, but I think earth scientists areextremely well equipped and positionedto address them. I’m proud to be part of ascience and a scientific society that canhelp the nation and the world addressthese challenges.

REFERENCES CITEDBlakely, R.J., Wells, R.E., Weaver, C.S., and Johnson, S.Y.,2002, Location, structure, and seismicity of the Seattlefault zone, Washington: Evidence from aeromagneticanomalies, geologic mapping, and seismic-reflection data:Geological Society of America Bulletin, v. 114 (in press).

Bourne, J., 2000, Louisiana’s Vanishing Wetlands: Going,Going...: Science, v. 289, p. 1860–1863.

Bornstein, R., and Lin, Q., 2000, Urban heat islands andsummertime convective thunderstorms in Atlanta: Threecase studies: Atmospheric Environment, v. 34, p. 507–516.

California Agricultural Statistics Service, 1999, Agriculturaloverview: A ten-year history of California’s agriculture:Sacramento, California, U.S. Department of Agriculture,www.nass.usda.gov/ca/bul/agstat/indexcas.htm (October2001).

Constanza, R., d’Arge, R., de Groot, R., Farber, S., Grasso,M., Hannon, B., Limburg, K., Naeem, S., O’Neill, R.V.,Paruelo, J., Raskin, R.G., Sutton, P., and van den Belt, M.,1997, The value of the world’s ecosystem services andnatural capital: Nature, v. 387, p. 253–260.

Figure 6. Map showing approximate locations of surface storagesites for spent nuclear fuel from commercial reactors and for otherhigh-level waste and radioactive materials within continentalUnited States. Illustration courtesy of U.S. Department of Energy.

GSA TODAY, DECEMBER 2001 47

Davenport, P.H., Christopher, T.K., Vardu, S., and Nolan,L.W., 1993, Geochemical mapping in Newfoundland and Labrador: Its role in establishing geochemical base-lines for the measurement of environmental change:Journal of Geochemical Exploration, v. 49, p. 177–200.

Fritts, H.C., 1984, Discussion of Bredehoeft, J., PhysicalLimitations of Water Resources, in Engelbert, E.A., andScheuring, A.F., eds., Water scarcity impacts on westernagriculture: Berkeley, California, University of California,p. 44–48.

Haugerud, R.A., Weaver, C.S., and Harless, J., 2001,Finding faults with LIDAR in the Puget Lowland: Seismol-ogical Research Letters: v. 72, no. 2, p. 253; see alsowww.spacedaily.com/news/radar-00d.html (October2001).

National Aeronautics and Space Administration, no date,Vegetation Canopy LIDAR: http://essp.gsfc.nasa.gov/vcl/,www.geog.umd.edu/vcl/ (October 2001).

California Habitat Protection Division, Wetlands, no date,What’s happening with coastal wetlands?: NationalOceanic and Atmospheric Administration and U.S.Department of Commerce, www.nmfs.noaa.gov/habitat/habitatprotection/wetlands4.htm (October 2001).

National Research Council, 2001, Grand challenges inenvironmental sciences: Washington, D.C., NationalAcademy of Sciences, http://books.nap.edu/books/0309072549/html/index.html (October 2001), 106 p.

National Research Council, 2000, Research needs insubsurface science: Washington, D.C., National Academyof Sciences, http://books.nap.edu/books/0309066468/html/index.html (October 2001), 159 p.

National Research Council, 1990, Rethinking high-levelradioactive waste disposal, available online as Appendix A in National Resource Council, 1992, Radioactive wasterepository licensing: Synopsis of a symposium, http://books.nap.edu/books/0309046912/html/index.html (October 2001).

Natural Resources Conservation Service, 1999, CaliforniaWildlife Habitat Incentives Program: U.S. Department of Agriculture, http://www.wl.fb-net.org/whip/ca.htm(October 2001).

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Quattrochi, D.A., Luvall, J.C., Rickman, D.L., Estes, M.G.,Laymon, C.A., and Howell, B.F., 2000, A decision supportinformation system for urban landscape managementusing thermal infrared data: Photogrammetric Engineering& Remote Sensing, v. 66, p. 1195–1207.

Thompson, R.S., Hostetler, S.W., Bartlein, P.J., andAnderson, K.H., 1998, A strategy for assessing potentialfuture changes in climate, hydrology, and vegetation in thewestern United States: U.S. Geological Survey Circular1153, http://greenwood.cr.usgs.gov/pub/circulars/c1153/index.html (October 2001).

Working Group on California Earthquake Probabilities,1999, Earthquake probabilities in the San Francisco BayRegion: 2000 to 2030—A summary of findings: U. S.Geological Survey Open-File Report 99-517, http://geopubs.wr.usgs.gov/open-file/of99-517/ (October 2001).