Sustainability Engineering and Practice
Sustainability Engineering and Practice EE 80
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Review TRENDS in Ecology and Evolution Vol2 l No6 June 2006 Full text provided by wwwsciencedirectcom SCIENCEltdDIRECT39 Global change ecology William H Schlesinger The Nicholas School of the Environment and Earth Sciences Duke University Durham NC 27708 USA Ecology has expanded from its traditional focus on organisms to include studies of the Earth as an integrated ecosystem Aided by satellite technologies and computer models of the climate of the Earth global change ecology now records basic parameters of our planet including its net primary productivity biogeo chemical cycling and effects of humans on it As I discuss here this new perspective shows us what must be done to transform human behaviors to enable the persistence of life on Earth under human stewardship Introduction When I was a graduate student during the early 1970s ecology was about organisms The prestigious places to publish were Ecology and The American Naturalist and the focus was on the number of individuals or species found in nature their rates of reproduction and the marvelous adaptations that enabled them to persist in their native habitats The research was usually done at eld stations each of us chose an idyllic place to spend the summer studying how nature is put together Today we see a huge emphasis on a broader view what is the effect of life on Earth What changes are we as the dominant species on the planet forcing on the habitats of all other species and how are we affecting the future prospects for life on Earth What can we do about our rapidly changing planet All these questions comprise global change science which lls the pages of an explosion of new journals that focus on the past and future of our planet Early studies of Earth system function There were harbingers to the birth of this new discipline During the late 1950s Roger Revelle commented that humans were performing an unreplicated global exper iment by raising the concentration of carbon dioxide 002 in our atmosphere with potentially serious but unknown consequences 1 By 1960 working with Revelle Dave Keeling 2 had shown that not only was the 002 concentration increasing but that one could also see a regular oscillation in its concentration that must be due to the photosynthesis of land plants in the temperate zone My colleague Dan Livingstone once said that the graph made him feel as if I had just put my nger on the beating living heart of the world 3 During the 1960s Gene Odum showed that one could trace the ow of energy through ecosystems focusing not so much on the individual species but on an attempt to understand the overall process by which the products of Corresponding author Schlesinger WH schlesindukeedu Available online 23 March 2006 photosynthesis either move to higher trophic levels such as humans or are dissipated in the environment 4 Herb Bormann and Gene Likens 5 did the same for the ow of material elements such as calcium potassium and other elements that anchor the biochemistry of all organisms Ecologists scrambled to study primary production and nutrient cycling as part of the International Biological Program IBP httpwww7nationalacademiesorg archivesInternational Biological Programhtml A milestone was reached when Robert Whittaker 6 and working independently Helmut Lieth 7 used these disparate eld studies to estimate the net primary production of the entire land surface of the Earth They were the rst to show just how much photosynthesis the biosphere had to work with each year Remarkably using rather crude methods they arrived at estimates between 50 and 60 Pg C yr 1 that are similar to measurements from satellites today 8 Most satellite estimates of plant productivity on Earth are based on the formulation of the Normalized Difference Vegetation Index NDVI developed by Compton Tucker and colleagues 9 and rst used to study changes in greenness from the Sahel of Africa 10 to high northern latitudes 11 I mark the beginning of global change science with the publication of The Biosphere as a special issue of Scienti c American in 1970 This was the rst time that I saw an integration of the science that viewed our planet as a closed ecosystem in which photosynthetic organisms captured sunlight energy enabling a profusion of other forms of life An array of articles outlined the global biogeochemical cycles and the emerging human impacts on them Not without controversy and criticism the publication of Limits to Growth in 1974 made many people realize how exponential growth in both population and economics would collide with the resources available on a nite plane 12 Global views of human impacts Documentation of human impacts on the biosphere was not long in coming In 1974 Mario Molina and Sherwood Rowland 13 predicted that chloro uorocarbons CFCs would destroy stratospheric ozone a forecast that is con rmed dramatically in satellite photos from NASA of the ozone hole from the 1980s to today Figure 1 This small human perturbation of the global chlorine cycle posed a real threat to the survival of life on Earth or at least on the land surface 14 Geochemists showed that the annual human production and mobilization of many important elements of the periodic table especially nitrogen phosphorus sulfur and most metals of economic interest rivaled that of nature 15 In 1986 Peter wwwsciencedirectcom 01695347 see front matter 2006 Elsevier Ltd All rights reserved doi101016jtree200603004 w 00L 92L 09L 9 N o o 922 N w U IIONU39I our the 912 0017 9217 0917 9117 009 Dobson units Dark gray lt 100 and gt 500 DU Figure 1 Toiai ooiumn ozone as recorded by the TOMS ssieime of NASA on 5 October 2005 one of the argest and deepest years on record for the ioss of stratospheric ozone over Antarctica Reproduced wiin permission from nno jwockygsfcnasagov Vitousek and colleagues 16 estimated that humans use or dominate approximately 40 of the terrestrial net primary production on Earth 1718 not a pretty picture for the future of most other species that share the planet with us General circulation models and satellite measure ments of the climate of the Earth con rmed what Svante Arrhenius 19 had predicted nearly a century earlier increasing levels of 002 in the atmosphere of the Earth a perturbation of the global carbon cycle would lead to a warmer planet as seen today 2021 These empirical studies were enriched by theorists During the 1960s NASA sponsored a program of science to examine closed systems with a desire to ascertain the minimum complexity that would be necessary for humans to survive in a spacecraft designed for longdistance explorations of the solar system 22 Of course then as now the Earth has been our planetary spaceship The 1979 publication of Gaia by James Lovelock 23 offered a provocative view that the biosphere on Earth was analogous to an organism having emergent traits such as homeostasis that fostered its own persistence Each species on Earth was thought to contribute in some small fashion to the stable conditions for life on Earth Although Gaia has few followers now the real impact of the book was that it made an entire generation of ecologists think broadly about planetary ecology In 1969 NASA took us to the Moon where we could look at our planet against the dark backdrop of space In 1976 NASA took its technology to Mars where it measured and photographed what we could expect on a planet without evidence of life And during the 1990s NASA applied its technology to planet Earth by launching www5ciencedirectcom TRENDS in Ecology and Evolution Vol21 No6 June 2006 349 the array of Earth Observing System EOS satellites that now monitor our planet recording basic characteristics of its temperature photosynthesis atmospheric chemistry and land cover all beamed down to receiving stations even as you read this httpeospsogsfcnasagov 24 Where we are today Through early global change science we gained a broad perspective on the impact of humans on nature There is little doubt that humans are now a major evolutionary force on Earth 25 and that our activities dominate its ecosystems both on land and in the sea 2627 Satellite views of nighttime lighting show the pervasive human presence on our planet 2829 Every ecosystem on Earth is now bathed in high 002 from fossil fuel combustion Chemicals of human origin are found on all continents 30 and are rapidly mixing to the deepest reaches of the sea 31 Even the re ection or albedo of the Earth as seen by earthshine on the Moon has increased as a result of a greater burden of atmospheric aerosols and clouds 32 The pristine eld stations that we visited as graduate students are of little relevance to most of the surface of the Earth that is now managed by humans and under rapid degradation under our stewardship What matters most for the organisms that we studied so diligently 30 years ago is not so much how they perform on Nature s stage but whether the stage will exist for them at all Priorities for global change science the sea There is much science left to do especially on the 70 of the surface of the Earth that is covered by salt water Although we have a fairly good estimate of the net primary production of the oceans 33 we have only a limited grasp of the sources of nitrogen phosphorus iron and silicon that fuel ocean productivity New research on sources of nitrogen to the oceans and its loss via anaerobic ammonia oxidizing bacteria has recently rewritten what we know about nitrogen cycling in the sea 34 Increasing atmospheric 002 levels have already lowered ocean pH by 01 and are likely to lead to much greater acidi cation during the rest of this century 35 Climatic change has also raised the temperature of the oceans and lowered the salinity over broad regions 3637 We are also likely to change marine net primary productivity as we alter the provision of essential elements to marine ecosystems through the dispersal of soils by wind erosion 38 There is every indication that we have overexploited the oceans Nearly 8 of oceanic productivity goes to support the current harvest of protein from ocean waters 39 Increasingly we see signs that the oceans are not an in nite sink in which to dilute the pollutants of industrialized society yet we lack a good understanding of the sources of mercury polybrominated organic compounds and other substances that might render oceanic sh un t for human consumption Are we polluting the last large domain on Earth or are some of ese compounds natural 40 42 Do species matter The original questions posed by NASA are ever more relevant today How much nature must be left in its 350 TRENDS in Ecology and Evolution Vol21 No6 June 2006 natural state for sustainable Earth system function Setting aside the ethics and aesthetics of preserving biodiversity how simple can we make an ecosystem while still seeing it function well without massive arti cial human interventions such as cultivation irrigation fertilization and pest control Work by David Tilman et al 43 which showed greater losses of nitrate beneath grassland ecosystems with depauperate species composition links healthy ecosystem function to high species diversity Does diversity beget stability or is there much redundancy of species that are pleasing to the eye but nonessential to the sustainability of a full planet New questions also face us What are the effects of the genetically modi ed organisms that enable us to supply new arti cial species to nature at the expense of the natural genetic diversity that is the raw material of evolution What can we expect from our efforts both purposeful and inadvertent to homogenize the ora and fauna of the Earth as rapid and frequent travel and trade accompany our globalization of commerce and culture How will we respond to disease pandemics As we anticipate and adapt to changes in the climate and chemistry of the Earth we need largescale and long term experiments to understand the response of biota to incremental COZ nitrogen and ozone and to changes in temperature and precipitation Experiments using Free Air 002 Enrichment FACE in forests 44 iron additions to seawater 45 and 15N additions to streams 46 have done much to elucidate the response of whole ecosystems to human perturbations The next phase of work should use factorial experiments so that we can understand how nature will respond to multiple stresses ortunately we have wonderful new tools with which to do our science better Molecular techniques will enable us to identify and understand the microbial communities that dominate so much of the biogeochemical cycling on Earth For example molecular systematics has been used to identify the bacteria catalyzing the anammox reaction converting NH4 to N2 in seawater 47 Mass spectrometry to analyze the proportion of stable isotopes in different pools and uxes has revolutionized how we recognize the importance of biology in controlling the chemistry of Earth Eddy covariance methods enable us to measure the net carbon exchange of large areas of the surface of the Earth eg 48 and remotesensing technologies will enable us to monitor the function of ecosystems with much greater sample frequency in space and time than was ever before possible These measurements are crucial if we are to build models of Earth system function that effectively couple surface processes to changes in climate and climatic forcings Mercifully each day we see increases in our computational abilities to synthesize all the data Beliefs and politics In some corners of the globe policy makers and politicians pay close attention to the science that shows what will happen to a planet under inattentive stewardship In much of the undeveloped world however the local population is perplexed about what to do to ensure a sustainable future when facing the immediate question of how to provide enough food and clean water to survive www5ciencedirectcom each day Sadly in other corners concern is shallow many of those who could afford to help believe that some type of divine intervention will carry us through a bottleneck of an exponentially rising human population and its increas ing demand for resources on a nite planet 49 They want no personal sacri ce Perhaps what we learned best from our early eld studies of ecology is that human behavior might not be far removed from that of other organisms Each squirrel on my bird tray feeds as if tomorrow is simply another day Many global change scient39sts talk of sustainability science Indeed there is heated debate about the reality and meaning of the phrase sustainable development In the preindustrial era humans lived in concert with nature No doubt it was a hard life but it was sustained for centuries The question we now face is whether we can live the way we aspire to today without degrading the life support systems of the planet that would sustain us tomorrow And w we must try our best simply to preserve the species that we studied so fervently just a few decades ago Global change science has a big agenda before it and little time in which to do it References 1 Revelle R and Suess HE 1957 Carbon dioxide exchange between the atmosphere and ocean and the question of an increase of atmospheric C02 during the past decades Tellus 9 18 27 Keeling CD 1960 The concentration and isotopic abundances of carbon dioxide in the atmosphere Tellus 1 0 203 Livingstone DA 1973 Summary and envoi In Carbon and the Biosphere Woodwell GM and Pecan EV eds pp 366 368 National Technical Information Service Odum ER 1968 Energy ow in ecosystems a historical review Am Zool 8 11 18 Bormann FH and Likens GE 1967 Nutrient cycling Science 155 424 429 m w as m m Whittaker RH 1970 Communities and Ecosystems MacMillan Lieth H 1975 Modeling the primary productivity of the world In Primary Productivity of the Biosphere Lieth H and Whittaker RH eds pp 7 263 Springer 8 Field CB et al 1998 Primary productivity of the biosphere integrating terrestrial and oceanic components Science 281 237 240 Tu er and Sellers PJ 1 86 Satellite remote sensing of primary production Int J Remote Sens 7 1395 1416 Tucker CJ et al 1990 Expansion and contraction of the Sahara desert from 1980 to 1990 Science 253 299 301 Myneni RB et al 1997 Increased plant growth in northern high latitudes from 1981 to 1991 Nature 386 698 702 Meadows DH et al 1974 The Limits to Growth Universe Books Molina MJ and Rowland ES 1974 Stratospheric sink for chloro uoromethanes chlorine atomcatalyzed destruction of ozone Nature 249 810 812 Graedel TE and Keene WC 1995 Tropospheric budget ofreactive chlorine Global Biogeochem Cycles 9 47 77 Bertine KK and Goldberg ED 1971 Fossil fuel combustion and the major sedimentary cycle Science 173 233 235 Vitousek PM et al 1986 Human appropriation of the products of photosynthesis Bioscience 36 368 373 7 Rojstaczer S et al 2001 Human appropriation of photosynthesis products Science 294 2549 2552 Imhoff ML et al 2004 Global patterns in human consumption ofnet primary production Nature 429 870 872 Arrhenius S 1896 On the in uence of carbonic acid in the air upon the temperature of the ground Lond Edin Dub Philos Mag J Sci 41 237 276 Harries JE et al 2001 Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 Nature 410 355 357 q to H o H H H m H w H as H m H m H H m H to m o