Biological Impacts ofClimate ChangeJohn P McCarty, University of Nebraska at Omaha, Omaha, NE, USA

L LaReesa Wolfenbarger, University of Nebraska at Omaha, Omaha, NE, USA

James A Wilson, University of Nebraska at Omaha, Omaha, NE, USA

Climate has far reaching impacts on biological systems. Survival and reproduction

depend on how well adapted individuals are to local climate patterns. Climate change

can disrupt the match between organisms and their local environment, reducing

survival and reproduction and causing subsequent impacts on populations or species’

distributions across geographic regions. Climate changemay benefit some species and

cause extinction for others. Cumulatively, it will alter biological communities and the

functioning of ecosystems. The Earth is already experiencing sufficient climate change

to affect biological systems;well-documented changes in plant and animal populations

are related to recent climate change. Predicting future biological impacts of climate

change remains a formidable challenge for science.

Introduction

One of the fundamental lessons from the science of ecologyis that patterns of climate strongly influence the distribu-tion and abundances of living organisms.Climate describesweather patterns for a given location over an extended pe-riod of time (e.g. 10+years). Climate is not just the averageconditions of temperature and precipitation but also theseasonal and annual weather variation, including the fre-quency and severity of extreme events such as storms ordrought. The Earth’s climatic patterns are now changingand there is increasing concern about how human activitiesare contributing to climate changes. The types of impactsclimate changewill haveon living systemshave far reachingconsequences for natural ecosystems and the people whodepend on the goods and services ecosystems provide.See also: Ecosystem Concepts: Introduction

The distribution of the general types of plants and an-imals or biomes around the world can be predicted withsome accuracy from climate patterns. General climate pat-terns are in turn generated by atmospheric circulation pat-terns caused by differential heating of the Earth’s surface,which determine the temperature and precipitation

patterns in a given area. Relatively minor changes in theoverall heat balance of the Earth can change atmosphericcirculation and result in local climate change more dra-matically than indicated by the degree of average warming.For example, a 18C increase in the world’s average tem-perature could result in some geographic regions experi-encingmuch greater than 18Cwarming,while other regionsshow little or no warming. Climate changes of this mag-nitude have been observed to impact species and entirebiological communities.One of the great challenges for biology today is to try to

understand how future changes in climate will impact bi-ological systems. Progress towards this goal depends onunderstanding how species respond to changes in climate,examining biological responses to recent climate changesand integrating this information in experiments and mod-els to try to understand how complex biological systemswill interact under future changing climate conditions.

How Climate Impacts Life

The basic components of climate – temperature and mois-ture – have pervasive impacts on organisms. Physiologicalprocesses define life, and at the most basic level these arechemical reactions. As such, they are subject to the un-avoidable relationship between temperature and the speedof chemical reactions.Whereas the rates of simple chemicalreactions increases as temperature increases, physiologicalprocesses respond in a more complex manner. This typi-cally involves a thermal optima where the reaction pro-ceeds most quickly. Physiological processes proceed more

Introductory article

Article Contents

. Introduction

. How Climate Impacts Life

. Observations of the Biological Impacts of Climate Change

. Trying to Understand the Future

. Summary

Online posting date: 15th March 2009

ELS subject area: Ecology

How to cite:McCarty, John P; Wolfenbarger, L LaReesa; and, Wilson, James A (March

2009) Biological Impacts of Climate Change. In: Encyclopedia of LifeSciences (ELS). John Wiley & Sons, Ltd: Chichester.

DOI: 10.1002/9780470015902.a0020480

ENCYCLOPEDIA OF LIFE SCIENCES & 2009, John Wiley & Sons, Ltd. www.els.net 1

slowly at temperatures above or below the thermal opti-mum. Most physiological processes are also water-based.All organisms face a major challenge: maintain an appro-priate water balance and temperature range for life-sustaining physiological processes while living in environ-ments that are too wet/dry and too cold/warm.

The climatewhere an organism lives dictates the specificsof this challenge, and organisms have evolved numerousadaptations to cope with hostile environments. Organismsare exposed to not just the average temperature and mois-ture conditions but also the variability associated with sea-sons andwith extreme events. Plants and animals copewithvariation in the environment in many ways. Some animalsmove to different geographic areas to avoid severe condi-tions (e.g. migration). Both plants and animals can reduceactivity when conditions are too severe: torpor in animalsand senescence in plants. See also: Ecology of WaterRelations and Thermoregulation; Ecology of WaterRelations in Plants

Climate and individuals

The physiologic health or condition of individuals acts asthe link between the habitat and population dynamics. In-dividuals poorly suited for their habitat may not obtainenough energy to maintain themselves in good conditionand may forego reproduction completely or until condi-tions in the habitat improve.

Climate can impact survival and reproduction for ani-mals that are able to regulate their body temperaturewithina narrow range even as surrounding air temperature varies,including endotherms such as birds and mammals. As thetemperature of the environment decreases relative to bodytemperature, the individual needs to expend energy to staywarm and may eventually reach the point where it can nolonger generate enough heat to maintain body tempera-ture. If the individual cannot move to a warmer environ-ment or obtain needed energy, it may die. At the otherextreme, as environmental temperature rises above bodytemperature, individuals need to expend energy and oftensignificant amounts of water, to stay cool. Once again ifsurrounding temperatures rise too high, the individual willno longer be able to regulate its body temperature and itcould die. Even if environmental temperatures donot reachthe extremes that cause death, the energy required tomain-tain internal conditions is no longer available for otherimportant activities such as reproduction.

Climate also has profound effects on the survival andreproduction of ectotherms; animals such as amphibians,reptiles and insects that are unable to regulate their bodytemperature independently of the surrounding tempera-ture of the environment. For these species, the rate ofphysiological processes determined by body temperaturedepends upon ambient temperature. As ambient temper-ature rises the rate of physiological processes increases in anonlinear fashion and increases more rapidly when initialtemperatures are low. For example a rate may triple acrossa temperature of 10–208C but may only double from

208C to 308C. Although ectotherms have a limited abilityto avoid the physiological consequences of changing envi-ronmental temperature, they have evolved a broad assort-ment of strategies for coping with a broad range of climateconditions. See also: Thermoregulation in Vertebrates;Vertebrate Metabolic VariationAs an adaptation to harsh environmental conditions,

especially cold temperatures, some ectotherms become in-active during unfavourable seasons of years, and climatechange will significantly alter the energy expenditures andbody condition of these organisms. Body condition inectotherms is tightly bound to reproductive output, timingto maturity and survival during inactive periods. Unlikehibernation in mammals, where individuals can regulatebody temperature independent of ambient temperature,ectotherms cannot. Because their hibernating metabolicrate is dependent on ambient temperature, warmer winterswill cause ectotherms to utilize more energy during hiber-nation than colder winters. Common toads (Bufo bufo)have shown a decline in body condition associated withincreasing temperatures which is also associated with de-creased annual survival. In addition, when ectotherms usemore energy to hibernate during warming winter, theyemerge from hibernation in poorer condition which re-duces reproduction. See also: Hibernation: Endotherms;Hibernation: Poikilotherms; Thermoregulation in Verte-brates: Acclimation, Acclimatization and AdaptationPlant physiology is also sensitive to temperature range

and moisture balance. Temperature and moisture interactto determine the rate of photosynthesis, the physiologicalprocess in which plants meet their energy needs and use thesun’s energy to synthesize carbohydrates from carbon di-oxide and water. Because plants have limited ability toregulate internal temperatures or to avoid temperature ex-tremes, many species become inactive during seasons whenconditions are unfavourable. Therefore, climate deter-mines the length of the growing season and the nongrowingseason when plants lack the necessary moisture for pho-tosynthesis or when temperatures drop below the freezingpoint of water. See also: Ecology of Water Relations inPlants; Photosynthesis: Ecology; Plant PhysiologicalResponses to Climate and Environmental Change

Climate and populations

A population consists of a collection of individuals, andpopulation size changes due to reproduction, immigration,mortality and emigration of these individuals. As such, apopulation can only grow when net individual reproduc-tion and/or immigration is greater than mortality and/oremigration, and decreases when the opposite occurs. Pop-ulation size is influenced by a complex interaction of directand indirect factors that change the energy budget of in-dividuals living in a population. Simply put, direct factorsare those that are abiotic and reflect changes to a popu-lation due to thermal stress, extreme weather or changes inprecipitation. Indirect factors represent changes to the bi-otic environment, typically manifested as changes in biotic

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interactions due to resource availability, community com-position and structure and predation pressure.

Most species have solved the challenges associatedwith aspecific range of climate conditions, and the occurrence ofthese conditions constrains the geographic range of a spe-cies. Outside of this range, factors driving populationsdown – mortality and emigration will overwhelm repro-duction and immigration, and populations will die out. Insome cases the correlation between specific climate condi-tions and the limits of geographic range can be quite close.For example, the northern limit of the wild madder plant(Rubia peregrina) in Europe corresponds closely to whereJanuary temperatures remain approximately 4.58C. InNorth America, the combination of temperature and pre-cipitation explains the distributions of many bird species,such as Northern Bobwhite (Colinus virginianus; Figure 1).

Although unfavourable climate can eliminate popula-tions, favourable climate is not a guarantee that popula-tions will occur or persist. Additional environmentalconditions besides climate may be unfavourable, or geo-graphic barriers may exist that prevent members of thepopulation from ever reaching a given geographic region.See also: Range Limits

Climate and interactions among species

Individuals interact with members of other species in a va-riety of ways. These include interactions among parasites,disease organisms, predators and prey and competition overcommon resources aswell asmutuallybeneficial interactionssuch as flowering plants producing nectar for the animalsthat pollinate their flowers. Through these interactions spe-cies may influence the population size and even geographicrange of other species. Interactions among species in a com-munity can produce indirect links between a population andclimate. For example, rush moths (Coleophora alticolella) inEngland tolerate the direct effects of climate associated withhigh elevations sites, but the plants on which the caterpillarsfeed do not produce enough seeds at high elevation, therebylimiting the range of the moth to low elevation sites withabundant food for caterpillars. Differences among species intheir abilities to cope with changes in climate can shift thebalance between competitors or allow new predators, path-ogens or parasites to invade a species range. See also:Coexistence; Community Ecology: An Introduction; Inter-specific Competition; Interspecific Interaction; Predation(Including Parasites and Disease) and Herbivory

Climate and communities and ecosystems

The community of plants and animals in a given areaemerges from the responses of individual species to climateand other physical factors. The species-specific nature ofthe factors limiting ranges means that biological commu-nities do not respond to climate as cohesive units but ratherare assemblages that reflect the tolerances of their compo-nent species. These assemblages of species are both familiarand have emergent properties such as diversity and

productivity. As climate changes it is probable that assem-blages of species that are now familiar will be broken up asspecies respond to new environmental conditions in differ-ent ways.Newassemblages will then emergewith their owncharacteristics and properties.Communities in turn are linked with the nonliving en-

vironment in ecosystems. Within an ecosystem, the flow ofenergy and matter among organisms is constrained by theability of plants to capture the sun’s energy in a form thatcanbe used by other organisms. In thisway, energy balanceforms the link between individual condition, populationdynamics and ecosystem functioning. Likewise, thesehigher-level processes that emerge from ecosystems havefar-reaching implications for humans through their im-pacts on nutrient, air and water cycles. See also: EcosystemConcepts: Introduction; Photosynthesis: Ecology

Observations of the Biological Impactsof Climate Change

TheEarth’s climate has been in a state of change formost ofthe history of life, and ample evidence exists to show howbiological systems respond to changes in temperature andmoisture. We know from fossils and other remains of longdead organisms that biological systems have undergonedramatic changes in response to past changes in climate.See also: Palaeoclimatology; PalaeoenvironmentsRecently, scientists have been able to observe how bio-

logical systems respond to ongoing climate change. Globalmean temperatures increased in the twentieth century,and while the average increase appears relatively modest(c. 0.748C), this warming has occurred unevenly across theglobe. Temperatures over land are warming faster thanover oceans, and warming of the arctic is occurring almosttwice as fast as the global average.Other changes in the environment follow from climate

change. Polar regions have had extensive warming of airand surface ocean temperatures. This has led to a decreasein the extent of Arctic sea ice, especially during summer.Similarly, theWest Antarctic Peninsula has also shown seaice melting. In the Northern Hemisphere the length of thesnow-free period has increased 5–6 days per decade since1972. In addition, the date that snow cover has melted hasbeen occurring earlier (3–5 days per decade).As scientists became aware of the rate of current climate

change, they observed long-term datasets to determine ifclimate change was impacting biological systems. Some ofthe longest running quantitative records of biological sys-tems are observations of seasonal biological events. Inmany areas of the globe, records of the timing, or pheno-logy, of events such as when birds migrate and when leavesor flowers appear in the spring go back decades or more.These data provide strong evidence forwidespread changesin the timing of biological events linked to the climatechanges experienced over the same time period. For ex-ample, Terry Root and her colleagues conducted a review

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30

Northern bobwhite (colinus virginianus)North America

20

10

−10

−20

−300 1000 2000

Precipitation (mm)3000 4000

0

Aver

age

tem

per

atur

e (°

C)

Incidence

0.8−10.6−0.80.4−0.60.2−0.40.05−0.2

AbsentNatureServe range

120

100 60

40

0 500 1000Kilometers

0.0

0.05−0.2

0.2−0.4

Breeding range

Legend

Incidence

Northern BobwhiteColinus virginianus

0.4−0.60.6−0.8

0.8−1.0

No data

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of 64 studies of biological events associated with the onsetof spring in 694 species of plants and animals; the resultsindicated that spring phenological events like migrationand flowering have been occurring earlier at a rate of 2–7days every decade.

Not all species will be able to cope with climate change bytracking favourable conditionsbecause the changing climatemight exceed the capacity of individuals toalter the timingofactivity. Desert dwelling ground squirrels face extreme heatduring summermonths and also lowwater availability. As aresult, ground squirrels enter a period of seasonal inactivity(aestivation) during the summer months to decrease ener-getic demands. However, as summers become warmer andprecipitation decreases, the length of the inactive season willincreasewhile thewet season, when squirrels obtain food foraestivation, shortens. Piute ground squirrels (Spermophilusmollis), from the western United States, have been shown toenter aestivation early in response to early spring drought. Ifthedrying trendcontinues to increase, these animalsmaynotacquire sufficient energy resources during the shortenedgrowing seasons to aestivate over the longer dry months.

Changing phenology may not always track favourableconditions if it disrupts or decouples species interactions orother biotic factors that influence populations. For exam-ple, Marmots in the mountains of Colorado spend thewinter hibernating and emerge from hibernation when airtemperature warms. As air temperatures have increased,marmots have been emerging from hibernation 23 daysearlier than they did in 1976. However, because winterprecipitation in the formof snow is increasing, deep snow isstill on the ground preventing plants from growing. There-fore, marmots must use their limited fat reserves for longerperiods in springwhile at the same time they have increasedenergetic demands and are preparing for reproduction.

Geographical ranges of species have expanded and con-tracted as climate factors have changed over the past de-cades. Historic datasets show that geographic ranges ofmanyNorthernHemisphere species are shifting northwardat rates consistent with observed climate change. Analysisof the geographic range of 59 species of birds in GreatBritain showed a northward shift in range averaging18.9 km in the span of only 20 years. In mountainous re-gions an analogous shift has been documented with speciesspreading to higher elevations where temperatures arecooler. These range expansions lead to a homogenizationof alpine plant communities and a decrease in specializedcommunities, particularly in alpine tundra associated withmountain peaks. See also: Alpine Ecosystems

Changes in species geographic ranges in recent decadesreflect the processes of local extinction of populations andinvasion of other areas creating newpopulations of species.For example, as climate has warmed isolated populationsofEdith’s checkerspot butterflies in the southern part of therange inNorthAmerica have beenmore likely to go extinctwhile new populations have emerged to the north of theirhistoric distribution. In this way, geographic ranges shiftwith climate change.In some cases it appears that changes in climate

have overwhelmed species’ abilities to respond. Amphib-ians living in the mountains of Central America may pro-vide a window into what the future might hold. TheMonteverde region of Costa Rica is world famous for itscloud forest and diverse community of frogs. Declines inpopulations of these frogs have been well documented inrecent decades and include the extinctionof the golden toad(Bufo periglenes). Population decline and species loss arelinked to the changing climate, including a reduction inmisty days a defining feature of cloud forests, but the fullexplanation is much more complex. Warmer nighttimetemperatures produce ideal growing conditions for a chy-trid fungus (Batrachochytrium dendrobatidis) that infectsamphibians and sometimes kills them. Frogs stressed bywarmer and drier climate are less able to resist fungal in-fection. As a result, populations decline and populationsand species go extinct.In addition to changes in populations and biological

communities, earlier spring warming and changes insummer climate have produced significant changes inthe fundamental energy dynamics of ecosystems. Satelliteand ground-based observations show that over the past25 years the transfer of energy from plants to higher trophiclevels (net primary productivity) has changed at bothan ecosystem and global scale. Ecosystems as diverse asnorthern tundra and the Amazon rainforest have shownincreases in productivity. Recently, productivity increasesassociated with warmer springs have been partly balancedby decreases in productivity from warmer and driersummers.

Trying to Understand the Future

Biological responses to future climate change will dependon the rate and magnitude of continued climate change.Sophisticated models of the Earth’s climate systemincorporate our best understanding of the variables

Figure 1 Much of the geographic range of species can be explained by climate. In the example shown above, Northern Bobwhite are widespread across

the southern two-thirds of the eastern United States. The map on left shows their geographic range and relative abundance based on the North American

Breeding Bird Survey. USDA Forest Service scientists evaluated the geographic distribution of Northern Bobwhite (and 146 other bird species) against

information about the climate and vegetation in the eastern United States. The importance of different climate and habitat variables in explaining geographic

range depends on the bird species. The figure on the right shows the combination of temperature and precipitation found in the eastern United States. The

coloured cells indicated the combinations of temperature and precipitation where Northern Bobwhite are found, while the light grey squares represent

combinations of temperature and precipitation found in the eastern United States where Northern Bobwhite are absent. Reproduced with permission from

Matthews SN, Iverson, LR, Prasad AM and Peters MP (2007). A Climate Change Atlas for 147 Bird Species of the Eastern United States [database]. Northern

Research Station, USDA Forest Service, Delaware, OH. http://www.nrs.fs.fed.us/atlas/bird.

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that interact to drive theEarth’s climate, but a fundamentaluncertainty for predicting climate change is how humanbehaviour will influence the increase in atmosphericgreenhouse gas concentrations. The IntergovernmentalPanel on Climate Change (IPCC) presents the most com-prehensive and authoritative synthesis of possible out-comes by examining several leading climate models andincorporating a range of ‘scenarios’ for future greenhousegas concentrations. The IPCC’s 2007 report suggestswarming is very likely to continue and accelerate duringthe twenty-first century. The average global temperatureby the end of this century is projected to increase 1.8–4.08Cor higher. As with past change, actual changes in temper-ature experienced by plants and animals will vary. Alpineand polar regions have experienced the greatest change inclimate and will likely continue to show dramatic effects ofglobal warming. See also: Biotic Response to ClimaticChange

How species might respond to climatechange

Based on observations of how biological systems have re-sponded to recent climate change, it is clear that climatechanges of the magnitude expected will have far reachingeffects on biological systems, including humans. Each spe-cies is likely to respond differently to changes in climate.For some species, climate will remain within the existingrange of tolerances. If local climate shifts outside the spe-cies’ range of tolerances, one of three responses will occur:adaptation (environmental or genetic change), relocationor extinction.

Changes in behaviour, timing of life history events(phenology), use of microhabitats and changes in physiol-ogy can all help species adjust to variations in climate. Forsome species, these capabilities already exist in individualsand responding to climate change will be relativelystraightforward (i.e. phenotypic plasticity). In other cases,the characteristics that determine the climate tolerance of aspecies will involve a more fundamental, genetically basedchange (evolution).

Range shifts in response to climate change

As climate changes, the geographic range of some specieswill shift to track changes in climatic conditions. The totalarea occupied by a species might increase, decrease or re-main constant. The geographic range of species will be aresult of how populations of individuals respond. This in-cludes both how the range occupied by a populationchanges and the gain or loss of geographically separatedpopulations. The potential for the range of species to movewith climate will depend on whether there is a net gain orloss of area with a suitable climate. Some species whoseranges are currently limited by climate may expand intosuitable areas whereas the potential range of other specieswill shrink. At a local scale suitable climate conditionsmaydisappear entirely. This might be most dramatic in

mountains where the potential shift in habitats to higherelevations is limited by the height of the mountains or nearthe poles where sea ice habitat will disappear.Another key factor will be the balance between how fast

climate shifts and how quickly species can respond. Howfar individuals or seeds and other propagules can spread ormove will limit changes in geographic range or migration.Freshwater plants and animalsmayhave evenmore limitedabilities to colonize new habitats as lakes and streamswarm. Although we might predict distributions of highlymobile species to change quickly, suitable habitat may de-pendnot just on climate conditions but also on the presenceor absence of other species or resources. Barriers to move-ment also exist in the form of mountains and water bodies(or land in the case of aquatic species). Finally, much of theEarth’s surface has been transformed by human activities,and the ability of populations of plants and animals tocolonize new areas in a human-dominated landscape isuncertain. See also: Dispersal: Biogeography

Evolution in response to climate change

As climate changes, heritable characteristics that increasesurvival or reproduction in the new climate will rapidlyspread in a population. The rate at which populations mayevolve or undergo change in its genetic make-up will de-termine whether a species can adapt to new climatic con-ditions. Although evolution can happen rapidly, not allspecies will be equally able to evolve in the face of climatechange. For evolution to occur rapidly, genetic variabilityin traits of interest needs to exist in the population; oth-erwise the rate of change would depend on a suitable mu-tation arising, an extremely rare event. Furthermore, smallor declining populations are less likely to adapt to changingenvironments due to their low levels of genetic variation.The rate atwhich evolutionary change couldproceed is alsoa function of the time between generations. Long-livedspecies such as trees will evolve more slowly than specieswith short generation times such as insects. See also:Adaptation and Constraint: Overview; Adaptation andNatural Selection:Overview;Natural Selection:Responsesto Current (Anthropogenic) Environmental Changes

Extinction in response to climate change

Not all species will be able to respond to changes in climate.Species that are unable to respond quickly enough will goextinct. The magnitude of extinctions could be immense.For some areas and groups of plants and animals, 15–37%of species could be at risk of extinction by 2050.Climate changes may increase the extinction rates of

species already at risk. Small populations will have limitedpotential to evolve in response to new conditions. Climatechangemay also exacerbate the very conditions that placedspecies at risk in the first place. For example, invasive spe-cies, disease and parasites pose a threat to many popula-tions, and the changing climate may facilitate the invasion

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of new threats into the range of species at risk. Invasivespecies are defined in part by their ability to colonize newareas andwould be expected to expand their ranges quicklyin response to climate change. Lack of suitable habitatplaces many species at risk of extinction. If climate changereduces habitat further, the species may be unable to re-cover from the loss and will go extinct. See also:Biodiversity – Threats; Extinction

Climate – ecology feedbacks

Climate clearly impacts biological systems but biologicalsystems can also influence climate by changing the amountof heat absorbed from the sun, releasing water vapour andaltering levels of carbon dioxide and other greenhousegasses in the atmosphere. The impact of this feedback onclimate is a considerable source of uncertainty for project-ing future effects of climate change on biological systems.Plants, both on land and in the ocean, absorb carbon di-oxide from the atmosphere during photosynthesis. Someofthe carbon trapped this way is transferred to higher trophiclevels when animals eat plants, some remains bound up inliving or dead plant matter and some is released back intothe atmosphere when dead plant material decays. The bal-ance between absorption of carbon dioxide from the at-mosphere and release back into the atmosphere hassignificant effects on the composition of the atmosphereand, ultimately, climate.

Behaviour of these so-called feedback loops is difficult topredict. Warming climate may extend the growing seasonin some areas, leading to more carbon dioxide being re-moved from the atmosphere. Whether this has an impacton climate will depend on whether the carbon remainstrapped in plantmaterial or is released into the atmosphere.

Climate change has the potential to disrupt currentstores of carbon trapped in plant matter and actually in-crease carbon dioxide in the atmosphere. In theArctic, vaststores of carbon are stored in peat and other plantmaterial.As the permafrost layer thaws thismaterial could decay at afaster rate, releasing the stored carbon in the form of car-bon dioxide and other greenhouse gasses. See also: GlobalCarbon Cycle

Effects of increasing carbon dioxide onbiological systems

Most of our attention is focused on changes in climatedriven by increasing concentrations of carbon dioxide inthe atmosphere. However, carbon dioxide can have othereffects on biological systems that will contribute to changesin the coming decades.

Carbon dioxide plays a key role in photosynthesis. Pho-tosynthesis rates can be higher as carbon dioxide concen-trations increase. Whether plants are able to takeadvantage of the enrichment of the atmosphere with car-bon dioxide will depend on whether they have the otherresources, such aswater andnutrients, to support increasedproductivity. Not all plants in a community will be equally

able to respond to increased carbon dioxide. Plants that areable to respondmay have a competitive advantage in com-munities. In the grasslands of North America, this mightlead to invasion of grasslands by trees and shrubs as woodyplants gain an advantage over grasses. See also: Photo-synthesis: Ecology; Plant Physiological Responses toClimate and Environmental ChangeIncreased carbon dioxide in the atmosphere is also hav-

ing far-reaching direct effects on the world’s oceans. Car-bon dioxide is soluble in water and decreases its pH byforming carbonic acid. Oceans have becomemore acidic inrecent years as atmospheric carbon dioxide levels have in-creased. Average pH of the ocean decreased from 8.16 to8.05 and could fall to 7.9 by 2100.Many aquatic organismsare sensitive to the acidity of water. For example, the car-bonate shells of marine animals can dissolve in acidic wa-ter. Increased acidity will further stress coral reefcommunities already suffering the effects of warmer watertemperatures. See also: Climate Change and Biogeochem-ical Impacts; Global Carbon Cycle

Models and experiments

One approach to understanding complex interactionsamong species and a changing environment is to take whatwe know about how species respond to climate (Figure 1)and combine it with output from global climate models toforecast how species or communities might respond to fu-ture conditions (Figure 2). Whereas these models do notpredict whether species will be able to respond to climatechange successfully, they can provide insights into howpotential habitat for different species might shift underdifferent climate conditions.Another approach to understanding complex interac-

tions is to try to expose current communities to conditionsthey might expect in the future. Long-term experimentshave artificiallywarmed plant communities, changedmois-ture levels and even increased carbon dioxide levels in thesurrounding air. These studies can be especially useful forunderstanding how changes in different aspects of the en-vironment can interact to influence biological systems. Forexample, trembling aspen (Populus tremuloides) exposed tohigher concentrations of carbon dioxide grow faster,whereas those exposed to increased ozone grow slower(Figure 3).When exposed to both carbon dioxide and ozonethe effects on growth are neutralized. Indirect effects ontrees appeared when trees were exposed to higher levels ofcarbon dioxide by impacting insects that live and feed onthe trees and by altering the competitive balance betweenaspen and sugar maple trees (Acer saccharum). See also:Global Carbon Cycle

Summary

There is little doubt that theEarth’s climatewill continue tochange in ways that impact biological systems. Whereasrecent and future changes in climate patterns are driven by

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Legend

White/red/jack pine

Spruce/fir

Longleaf/slash pine

Loblolly/shortleaf pine

Oak/pine

Oak/hickory

Oak/gum/cypress

Elm/ash/cottonwood

Maple/beech/birch

Aspen/birch

No data

Current/FIA Current modelled

Average of 3 GCM - low Average of 3 GCM - high

Figure 2 Mathematical models provide one approach for helping us understand how changes in climate will impact biological systems. These maps show

the current geographic range of forest types as well asmodelled output based on current climate and two scenarios of future climate. Current forest types (panel

A) are based on the USDA Forest Service’s Forest Inventory Analysis (FIA) data. Information about the geographic range of 134 tree species was evaluated

against 38 environmental variables to generate predictive models. The utility of the models can be evaluated by inserting current climate conditions into the

models and comparing the output (panel B) to current distributions of forest types (panel A). The general correlation between the actual current FIA data and the

modelled current distributions indicates that much of the variation in where the forest types occur can be explained by combinations of climate variables.

This correlation also suggests that the Forest Servicemodel can be used tomodel potential habitat under future climate conditions. The scientists took the output

from three widely used global climate models under two scenarios used by the Intergovernmental Panel on Climate Change. The ‘Low’ scenario assumes

that emissionsof greenhouse caseswill be significantly reduced,while the ‘High’ scenario assumes that current emission trendswill continue. PanelsC andDshow

how the potential habitat for forests might change in the future. Note in particular the loss of potential habitat for northern forest types such as Spruce-Fir

forests that are currently found in the northern tier of states but which might disappear in the future. Reproduced with permission from: Prasad AM, Iverson LR,

Matthews S and Peters M (2007). A Climate Change Atlas for 134 Forest Tree Species of the Eastern United States [database]. Northern Research Station,

USDA Forest Service, Delaware, OH. http://www.nrs.fs.fed.us/atlas/tree.

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an overall global warming trend, it is important to remem-ber that biological systems interact with local climate pat-terns, not the global average. Understanding futureimpacts of climate change is not a simple matter of ask-ing how biological systems respond to 28C or 48C changesin temperature, but the more complicated task of how 28Cor 48C or more 8C warming of the Earth’s system will im-pact the climate patterns where the biological system ofinterest resides. See also: Global Change – ContemporaryConcerns

It is clear from both ancient and recent climate changethat while some species will adapt to new climate condi-tions, not all species will have the ability to respond tochanges in climate. Extinctions will occur; current com-munities of species may disassemble as species responddifferently to rapid climate change; new species’ assem-blages will emerge. The fates of those species faced with therapid changes in climate expected in the comingdecades areuncertain, but their extinction will result in permanent,cascading changes to the ecosystems that provide humansocieties with goods and services we depend on and value.

Further Reading

Bjork RG and Molau U (2007) Ecology of alpine snowbeds and

the impact of global warming.Arctic, Antarctic, and Alpine Re-

search 39: 34–43.

Bradley KL and Pregitzer KS (2007) Ecosystem assembly and

terrestrial carbon balance under elevated CO2. Trends in Ecol-

ogy and Evolution 22: 538–547.

IPCC (2007) Climate change 2007: impacts, adaptation and vul-

nerability. In: Parry ML, Canziani OF, Palutikof JP, van der

Linden PJ andHansonCE (eds)Contribution ofWorkingGroup

II to the Fourth Assessment Report of the Intergovernmental

Panel on Climate Change, p. 976. Cambridge, UK: Cambridge

University Press.

IPCC (2007) Climate change 2007: synthesis report. In: Core

WritingTeam, PachauriRKandReisingerA (eds)Contribution

of Working Groups I, II and III to the Fourth Assessment Report

of the Intergovernmental Panel on Climate Change, p. 104.

Geneva, Switzerland: IPCC.

Jurasinski G and Kreyling J (2007) Upward shift of alpine plants

increases floristic similarity of mountain summits. Journal of

Vegetation Science 18: 711–718.

Lovejoy TE and Hannah L (2005) Climate Change and Biodiver-

sity. New Haven, CT: Yale University Press.

McCarty JP (2001) Ecological consequences of recent climate

change. Conservation Biology 15: 320–331.

Pounds JA, Bustamante MR, Coloma LA et al. (2006) Wide-

spread amphibian extinctions from epidemic disease driven by

global warming. Nature 439: 161–167.

ReadingCJ (2007) Linking global warming to amphibian declines

through its effects on female body condition and survivorship.

Oecologia 151: 125–131.

Willmer P, Stone G and Johnston I (2005) Environmental Phys-

iology of Animals, Second Edition. Oxford, UK: Blackwell

Publishing, 754pp.

Figure 3 The Aspen FACE (Free Air CarbonDioxide Enrichment) Experiment is growing trembling aspen trees in the open under carbon dioxide levels similar to

those expected to occur late in the twenty-first century. The pipes surrounding the growing trees release carbon dioxide, mimicking the effects of altered

atmosphere in a field setting where plants interact with each other and with other environmental variables in a natural setting. Photograph by JP McCarty.

Biological Impacts of Climate Change