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Terrestrial and Inland
Water Systems
Coordinating Lead Authors:
Josef Settele (Germany), Robert Scholes (South Africa)
Lead Authors:
Richard A. Betts (UK), Stuart Bunn (Australia), Paul Leadley (France), Daniel Nepstad (USA),
Jonathan T. Overpeck (USA), Miguel Angel Taboada (Argentina)
Contributing Authors:
Rita Adrian (Germany), Craig Allen (USA), William Anderegg (USA), Celine Bellard (France),
Paulo Brando (Brazil), Louise P. Chini (New Zealand), Franck Courchamp (France),
Wendy Foden (South Africa), Dieter Gerten (Germany), Scott Goetz (USA), Nicola Golding (UK),
Patrick Gonzalez (USA), Ed Hawkins (UK), Thomas Hickler (Germany), George Hurtt (USA),
Charles Koven (USA), Josh Lawler (USA), Heike Lischke (Switzerland), Georgina M. Mace (UK),
Melodie McGeoch (Australia), Camille Parmesan (USA), Richard Pearson (UK),
Beatriz Rodriguez-Labajos (Spain), Carlo Rondinini (Italy), Rebecca Shaw (USA), Stephen Sitch
(UK), Klement Tockner (Germany), Piero Visconti (UK), Marten Winter (Germany)
Review Editors:
Andreas Fischlin (Switzerland), José M. Moreno (Spain), Terry Root (USA)
Volunteer Chapter Scientists:
Martin Musche (Germany), Marten Winter (Germany)
This chapter should be cited as:
Settele
, J., R. Scholes, R. Betts, S. Bunn, P. Leadley, D. Nepstad, J.T. Overpeck, and M.A. Taboada, 2014:
Terrestrial and inland water systems. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability.
Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach,
M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy,
S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA, pp. 271-359.
4
272
Executive Summary ........................................................................................................................................................... 274
4.1. Past Assessments ..................................................................................................................................................... 278
4.2. A Dynamic and Inclusive View of Ecosystems ........................................................................................................ 278
4.2.1. Ecosystems, Adaptation, Thresholds, and Tipping Points ................................................................................................................... 278
4.2.2. Methods and Models Used ............................................................................................................................................................... 279
4.2.3. Paleoecological Evidence .................................................................................................................................................................. 279
4.2.4. Multiple Stressors Interacting with Climate Change ......................................................................................................................... 283
4.2.4.1.Land Use and Cover Change ................................................................................................................................................ 283
Box 4-1. Future Land Use Changes .................................................................................................................................. 284
4.2.4.2.Nitrogen Deposition ............................................................................................................................................................. 285
4.2.4.3.Tropospheric Ozone .............................................................................................................................................................. 286
4.2.4.4.Rising Carbon Dioxide .......................................................................................................................................................... 287
4.2.4.5.Diffuse and Direct Radiation ................................................................................................................................................ 288
4.2.4.6.Invasive and Alien Species ................................................................................................................................................... 288
4.3. Vulnerability of Terrestrial and Freshwater Ecosystems to Climate Change .......................................................... 290
4.3.1. Changes in the Disturbance Regime ................................................................................................................................................. 290
4.3.2. Observed and Projected Change in Ecosystems ................................................................................................................................ 290
4.3.2.1.Phenology ............................................................................................................................................................................ 291
4.3.2.2.Primary Productivity ............................................................................................................................................................. 292
4.3.2.3.Biomass and Carbon Stocks ................................................................................................................................................. 293
4.3.2.4.Evapotranspiration and Water Use Efficiency ....................................................................................................................... 294
4.3.2.5.Changes in Species Range, Abundance, and Extinction ........................................................................................................ 294
4.3.3. Impacts on and Risks for Major Systems .......................................................................................................................................... 301
4.3.3.1.Forests and Woodlands ........................................................................................................................................................ 301
Box 4-2. Tree Mortality and Climate Change ................................................................................................................... 306
4.3.3.2.Dryland Ecosystems: Savannas, Shrublands, Grasslands, and Deserts .................................................................................. 308
Box 4-3. A Possible Amazon Basin Tipping Point ............................................................................................................. 309
4.3.3.3.Rivers, Lakes, Wetlands, and Peatlands ................................................................................................................................. 312
4.3.3.4.Tundra, Alpine, and Permafrost Systems ............................................................................................................................... 314
Box 4-4. Boreal–Tundra Biome Shift ................................................................................................................................ 316
4.3.3.5.Highly Human-Modified Systems ......................................................................................................................................... 317
4.3.4. Impacts on Key Ecosystem Services .................................................................................................................................................. 319
4.3.4.1.Habitat for Biodiversity ........................................................................................................................................................ 319
4.3.4.2.Timber and Pulp Production ................................................................................................................................................. 320
4.3.4.3.Biomass-Derived Energy ....................................................................................................................................................... 320
4.3.4.4.Pollination, Pest, and Disease Regulation ............................................................................................................................. 320
4.3.4.5.Moderation of Climate Change, Variability, and Extremes ................................................................................................... 321
Table of Contents
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4.4. Adaptation and Its Limits ....................................................................................................................................... 321
4.4.1. Autonomous Adaptation by Ecosystems and Wild Organisms .......................................................................................................... 321
4.4.1.1.Phenological ........................................................................................................................................................................ 321
4.4.1.2.Evolutionary and Genetic ..................................................................................................................................................... 322
4.4.1.3.Migration of Species ............................................................................................................................................................ 324
4.4.2. Human-Assisted Adaptation ............................................................................................................................................................. 324
4.4.2.1.Reduction of Non-Climate Stresses and Restoration of Degraded Ecosystems ..................................................................... 324
4.4.2.2.The Size, Location, and Layout of Protected Areas ............................................................................................................... 324
4.4.2.3.Landscape and Watershed Management ............................................................................................................................. 324
4.4.2.4.Assisted Migration ............................................................................................................................................................... 325
4.4.2.5.Ex Situ Conservation ............................................................................................................................................................ 326
4.4.3. Consequences and Costs of Inaction and Benefits of Action ............................................................................................................ 326
4.4.4. Unintended Consequences of Adaptation and Mitigation ................................................................................................................ 327
4.5. Emerging Issues and Key Uncertainties .................................................................................................................. 328
References ......................................................................................................................................................................... 328
Frequently Asked Questions
4.1: How do land use and land cover changes cause changes in climate? .............................................................................................. 282
4.2: What are the non-greenhouse gas effects of rising carbon dioxide on ecosystems? ........................................................................ 287
4.3: Will the number of invasive alien species increase as a result of climate change? ........................................................................... 289
4.4: How does climate change contribute to species extinction? ............................................................................................................ 295
4.5: Why does it matter if ecosystems are altered by climate change? .................................................................................................... 319
4.6: Can ecosystems be managed to help them and people to adapt to climate change? ...................................................................... 325
4.7: What are the economic costs of changes in ecosystems due to climate change? ............................................................................. 326
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Executive Summary
The planet’s biota and ecosystem processes were strongly affected by past climate changes at rates of climate change lower
than those projected during the 21st century under high warming scenarios (e.g., Representative Concentration Pathway 8.5
(RCP8.5)) (high confidence). Most ecosystems are vulnerable to climate change even at rates of climate change projected under
low- to medium-range warming scenarios (e.g., RCP2.6 to RCP6.0).
The paleoecological record shows that global climate changes
comparable in magnitudes to those projected for the 21st century under all scenarios resulted in large-scale biome shifts and changes in
community composition; and that for rates projected under RCP6 and 8.5 were associated with species extinctions in some groups (high
confidence). {4.2.3}
Climate change is projected to be a powerful stressor on terrestrial and freshwater ecosystems in the second half of the 21st
century, especially under high-warming scenarios such as RCP6.0 and RCP8.5 (high confidence). Direct human impacts such as
land use and land use change, pollution, and water resource development will continue to dominate the threats to most
freshwater (high confidence) and terrestrial (medium confidence) ecosystems globally over the next 3 decades. Changing climate
exacerbates other impacts on biodiversity (high confidence).
Ecosystem changes resulting from climate change may not be fully apparent
for several decades, owing to long response times in ecological systems (medium confidence). Model-based projections imply that under low to
moderate warming scenarios (e.g., RCP2.6 to RCP6.0), direct land cover change will continue to dominate over (and conceal) climate-induced
change as a driver of ecosystem change at the global scale; for higher climate change scenarios, some model projections imply climate-driven
ecosystem changes sufficiently extensive to equal or exceed direct human impacts at the global scale (medium confidence). In high-altitude
and high-latitude freshwater and terrestrial ecosystems, climate changes exceeding those projected under RCP2.6 will lead to major changes in
species distributions and ecosystem function, especially in the second half of the 21st century (high confidence). {4.2.4, 4.3.2.5, 4.3.3, 4.3.3.1,
4.3.3.3, 4.4.1.1}
When terrestrial ecosystems are substantially altered (in terms of plant cover, biomass, phenology, or plant group dominance),
either through the effects of climate change or through other mechanisms such as conversion to agriculture or human settlement,
the local, regional, and global climates are also affected (high confidence).
The feedbacks between terrestrial ecosystems and climate
include, among other mechanisms, changes in surface albedo, evapotranspiration, and greenhouse gas (GHG) emissions and uptake. The physical
effects on the climate can be opposite in direction to the GHG effects, and can materially alter the net outcome of the ecosystem change on the
global climate (high confidence). The regions where the climate is affected may extend beyond the location of the ecosystem that has changed.
{4.2.4.1, 4.3.3.4}
Rising water temperatures, due to global warming, will lead to shifts in freshwater species distributions and worsen water quality
problems, especially in those systems experiencing high anthropogenic loading of nutrients (high confidence).
Climate change-
induced changes in precipitation will substantially alter ecologically important attributes of flow regimes in many rivers and wetlands and
exacerbate impacts from human water use in developed river basins (medium confidence). {4.3.3.3, Box CC-RF}
Many plant and animal species have moved their ranges, altered their abundance, and shifted their seasonal activities in response
to observed climate change over recent decades (high confidence). They are doing so now in many regions and will continue to do
so in response to projected future climate change (high confidence).
The broad patterns of species and biome shifts toward the poles and
higher in altitude in response to a warming climate are well established for periods thousands of years in the past (very high confidence). These
general patterns of range shifts have also been observed over the last few decades in some well-studied species groups such as insects and
birds and can be attributed to observed climatic changes (high confidence). Interactions between changing temperature, precipitation, and land
use can sometimes result in range shifts that are downhill or away from the poles. Certainty regarding past species movements in response to
changing climate, coupled with projections from a variety of models and studies, provides high confidence that such species movements will be
the norm with continued warming. Under all RCP climate change scenarios for the second half of the 21st century, with high confidence:
(1) community composition will change as a result of decreases in the abundances of some species and increases in others; and (2) the
seasonal activity of many species will change differentially, disrupting life cycles and interactions between species. Composition and seasonal
change will both alter ecosystem function. {4.2.1, 4.2.3, 4.3.2, 4.3.2.1, 4.3.2.5, 4.3.3, 4.4.1.1}
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Many species will be unable to move fast enough during the 21st century to track suitable climates under mid- and high-range
rates of climate change (i.e., RCP4.5, RCP6.0, and RCP8.5 scenarios) (medium confidence).
The climate velocity (the rate of movement
of the climate across the landscape) will exceed the maximum velocity at which many groups of organisms, in many situations, can disperse or
migrate, except after mid-century in the RCP2.6 scenario. Populations of species that cannot keep up with their climate niche will find themselves
in unfavorable climates, unable to reach areas of potentially suitable climate. Species occupying extensive flat landscapes are particularly
vulnerable because they must disperse over longer distances than species in mountainous regions to keep pace with shifting climates. Species
with low dispersal capacity will also be especially vulnerable: examples include many plants (especially trees), many amphibians, and some
small mammals. For example, the maximum observed and modeled dispersal and establishment rates for mid- and late-successional tree
species are insufficient to track climate change except in mountainous areas, even at moderate projected rates of climate change. Barriers to
dispersal, such as habitat fragmentation, prior occupation of habitat by competing species, and human-made impediments such as dams on
rivers and urbanized areas on land, reduce the ability of species to migrate to more suitable climates (high confidence). Intentional and
accidental anthropogenic transport can speed dispersal. {4.3.2.5, 4.3.3.3}
Large magnitudes of climate change will reduce the populations, vigor, and viability of species with spatially restricted populations,
such as those confined to small and isolated habitats, mountaintops, or mountain streams, even if the species has the biological
capacity to move fast enough to track suitable climates (high confidence).
The adverse effects on restricted populations are modest for
low magnitudes of climate change (e.g., RCP2.6) but very severe for the highest magnitudes of projected climate change (e.g., RCP8.5).
{4.3.2.5, 4.3.3.4, 4.3.4.1}
The capacity of many species to respond to climate change will be constrained by non-climate factors (high confidence), including
but not limited to the simultaneous presence of inhospitable land uses, habitat fragmentation and loss, competition with alien species, exposure
to new pests and pathogens, nitrogen loading, and tropospheric ozone. {4.2.4.6, 4.3.3.5, Figure 4-4}
The establishment, growth, spread, and survival of populations of invasive alien species have increased (high confidence), but
the ability to attribute alien species invasion to climate change is low in most cases. Some invasive alien species have traits that favor
their survival and reproduction under changing climates. Future movement of species into areas where they were not present historically will
continue to be driven mainly by increased dispersal opportunities associated with human activities and by increased disturbances from natural
and anthropogenic events, in some cases facilitated and promoted by climate change. {4.2.4.6, Figure 4-4}
A large fraction of terrestrial and freshwater species face increased extinction risk under projected climate change during and
beyond the 21st century, especially as climate change interacts with other pressures, such as habitat modification, overexploitation,
pollution, and invasive species (high confidence).
The extinction risk is increased under all RCP scenarios, and the risk increases with both
the magnitude and rate of climate change. While there is medium confidence that recent warming contributed to the extinction of some species
of Central American amphibians, there is generally very low confidence that observed species extinctions can be attributed to recent climate
change. Models project that the risk of species extinctions will increase in the future owing to climate change, but there is low agreement
concerning the fraction of species at increased risk, the regional and taxonomic focus for such extinctions and the time frame over which
extinctions could occur. Modeling studies and syntheses since the AR4 broadly confirm that a large proportion of species are projected to be at
increased risk of extinction at all but the lowest levels of climate warming (RCP2.6). Some aspects leading to uncertainty in the quantitative
projections of extinction risks were not taken into account in previous models; as more realistic details are included, it has been shown that the
extinction risks may be either under- or overestimated when based on simpler models. {4.3.2.5}
Terrestrial and freshwater ecosystems have sequestered about a quarter of the carbon dioxide (CO
2
) emitted to the atmosphere
by human activities in the past 3 decades (high confidence).
The net fluxes out of the atmosphere and into plant biomass and soils show
large year-to-year variability; as a result there is low confidence in the ability to determine whether the net rate at which carbon has been
taken up by terrestrial ecosystems at the global scale has changed between the decades 1991–2000 and 2001–2010. There is high confidence
that the factors causing the current increase in land carbon include the positive effects of rising CO
2
on plant productivity, a warming climate,
nitrogen deposition, and recovery from past disturbances, but low confidence regarding the relative contribution by each of these and other
factors. {4.2.4.1, 4.2.4.2, 4.2.4.4, 4.3.2.2, 4.3.2.3, WGI AR5 6.3.1, 6.3.2.6}
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The natural carbon sink provided by terrestrial ecosystems is partially offset at the decadal time scale by carbon released
through the conversion of natural ecosystems (principally forests) to farm and grazing land and through ecosystem degradation
(high confidence). Carbon stored in the terrestrial biosphere is vulnerable to loss back to the atmosphere as a result of the direct
and indirect effects of climate change, deforestation, and degradation (high confidence). The net transfer of CO
2
from the
atmosphere to the land is projected to weaken during the 21st century (medium confidence). The direct effects of climate change on
stored terrestrial carbon include high temperatures, drought, and windstorms; indirect effects include increased risk of fires and pest and disease
outbreaks. Experiments and modeling studies provide medium confidence that increases in CO
2
up to about 600 ppm will continue to enhance
photosynthesis and plant water use efficiency, but at a diminishing rate; and high confidence that low availability of nutrients, particularly
nitrogen, will limit the response of many natural ecosystems to rising CO
2
. There is medium confidence that other factors associated with
global change, including high temperatures, rising ozone concentrations, and in some places drought, decrease plant productivity by amounts
comparable in magnitude to the enhancement by rising CO
2
. There are few field-scale experiments on ecosystems at the highest CO
2
concentrations projected by RCP8.5 for late in the century, and none of these include the effects of other potential confounding factors.
{4.2.4, 4.2.4.1, 4.2.4.2, 4.2.4.3, 4.2.4.4, 4.3.2.2, 4.3.3.1, Box 4-3, Box CC-VW, WGI AR5 6.4.3.3}
Increases in the frequency or intensity of ecosystem disturbances such as droughts, wind storms, fires, and pest outbreaks have
been detected in many parts of the world and in some cases are attributed to climate change (medium confidence). Changes in
the ecosystem disturbance regime beyond the range of natural variability will alter the structure, composition, and functioning
of ecosystems (high confidence).
Ecological theory and experimentation predict that ecological change resulting from altered disturbance
regimes will be manifested as relatively abrupt and spatially patchy transitions in ecosystem structure, composition, and function, rather than
gradual and spatially uniform shifts in location or abundance of species (medium confidence). {4.2.4.6, 4.3.3, 4.3.2.5, Box 4-3, Box 4-4,
Figure 4-10}
Increased tree death has been observed in many places worldwide, and in some regions has been attributed to climate change
(high confidence). In some places it is sufficiently intense and widespread as to result in forest dieback (low confidence). Forest
dieback is a major environmental risk, with potentially large impacts on climate, biodiversity, wood production, water quality, amenity, and
economic activity. In detailed regional studies in western and boreal North America, the tree mortality observed over the past few decades has
been attributed to the effects of high temperatures and drought, or to changes in the distribution and abundance of insect pests and
pathogens related, in part, to warming (high confidence). Tree mortality and associated forest dieback will become apparent in many regions
sooner than previously anticipated (medium confidence). Earlier projections of increased tree growth and enhanced forest carbon sequestration
due to increased growing season duration, rising CO
2
concentration, and atmospheric nitrogen deposition must be balanced by observations
and projections of increasing tree mortality and forest loss due to fires and pest attacks. The consequences for the provision of timber and other
wood products are projected to be highly variable between regions and products, depending on the balance of the positive versus negative
effects of global change. {4.3.2, 4.3.3.1, 4.3.3.4, 4.3.3.5, 4.3.4, 4.3.4.2, Box 4-2, Box 4-3}
There is a high risk that the large magnitudes and high rates of climate change associated with low-mitigation climate scenarios
(RCP4.5 and higher) will result within this century in abrupt and irreversible regional-scale change in the composition, structure,
and function of terrestrial and freshwater ecosystems, for example in the Amazon (low confidence) and Arctic (medium confidence),
leading to substantial additional climate change.
There are plausible mechanisms, supported by experimental evidence, observations, and
model results, for the existence of ecosystem tipping points in both boreal-tundra Arctic systems and the rainforests of the Amazon basin.
Continued climate change will transform the species composition, land cover, drainage, and permafrost extent of the boreal-tundra system,
leading to decreased albedo and the release of GHGs (medium confidence). Adaptation measures will be unable to prevent substantial change
in the boreal-Arctic system (high confidence). Climate change alone is not projected to lead to abrupt widespread loss of forest cover in the
Amazon during this century a (medium confidence), but a projected increase in severe drought episodes, together with land use change and
forest fire, would cause much of the Amazon forest to transform to less dense, drought- and fire-adapted ecosystems, and in doing so put a
large stock of biodiversity at elevated risk, while decreasing net carbon uptake from the atmosphere (low confidence). Large reductions in
deforestation, as well as wider application of effective wildfire management, lower the risk of abrupt change in the Amazon, as well as the
impacts of that change (medium confidence). {4.2.4.1, 4.3.3.1.1, 4.3.3.1.3, 4.3.3.4, Figure 4-8, Box 4-3, Box 4-4}
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Management actions can reduce, but not eliminate, the risk of impacts to terrestrial and freshwater ecosystems due to climate
change, as well as increase the inherent capacity of ecosystems and their species to adapt to a changing climate (high confidence).
The capacity for natural adaptation by ecosystems and their constituent organisms is substantial, but for many ecosystems and species it will
be insufficient to cope with projected rates and magnitudes of climate change in the 21st century without substantial loss of species and
ecosystem services, under medium-range warming (e.g., RCP6.0) or high-range warming scenarios (e.g., RCP8.5) (medium confidence). The
capacity for ecosystems to adapt to climate change can be increased by reducing the other stresses operating on them; reducing the rate and
magnitude of climate change; reducing habitat fragmentation and increasing connectivity; maintaining a large pool of genetic diversity and
functional evolutionary processes; assisted translocation of slow moving organisms or those whose migration is impeded, along with the
species on which they depend; and manipulation of disturbance regimes to keep them within the ranges necessary for species persistence and
sustained ecosystem functioning. {4.4, 4.4.1, 4.4.2}
Adaptation responses to climate change in the urban and agricultural sectors can have unintended negative outcomes for
terrestrial and freshwater ecosystems (medium confidence). For example, adaptation responses to counter increased variability of water
supply, such as building more and larger impoundments and increased water extraction, will in many cases worsen the direct effects of climate
change in freshwater ecosystems. {4.3.3.3, 4.3.4.6}
Widespread transformation of terrestrial ecosystems in order to mitigate climate change, such as carbon sequestration through
planting fast-growing tree species into ecosystems where they did not previously occur, or the conversion of previously
uncultivated or non-degraded land to bioenergy plantations, will lead to negative impacts on ecosystems and biodiversity (high
confidence).
For example, the land use scenario accompanying the mitigation scenario RCP2.6 features a large expansion of biofuel production,
displacing natural forest cover. {4.2.4.1, 4.4.4}
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4.1. Past Assessments
The topics assessed in this chapter were last assessed by the IPCC in
2007, principally in WGII AR4 Chapters 3 (Kundzewicz et al., 2007) and
4
(Fischlin et al., 2007), but also in WGII AR4 Sections 1.3.4 and 1.3.5
(Rosenzweig et al., 2007). The WGII AR4 SPM statedObservational
evidence from all continents and most oceans shows that many natural
systems are being affected by regional climate changes, particularly
temperature increases, though they noted that documentation of
observed changes in tropical regions and the Southern Hemisphere was
sparse (Rosenzweig et al., 2007). Fischlin et al. (2007) found that 20 to
30% of the plant and animal species that had been assessed to that time
were considered to be at increased risk of extinction if the global average
temperature increase exceeds 2°C to 3°C above the preindustrial level
with medium confidence, and that substantial changes in structure and
functioning of terrestrial, marine, and other aquatic ecosystems are very
likely under that degree of warming and associated atmospheric CO
2
concentration. No time scale was associated with these findings. The
carbon stocks in terrestrial ecosystems were considered to be at high
risk from climate change and land use change. The report warned that
the capacity of ecosystems to adapt naturally to the combined effect of
climate change and other stressors is likely to be exceeded if greenhouse
gas (GHG) emission continued at or above the then-current rate.
4.2. A Dynamic and Inclusive View
of Ecosystems
There are three aspects of the contemporary scientific view of ecosystems
that are important to know for policy purposes. First, ecosystems usually
have imprecise and variable boundaries. They span a wide range of
spatial scales, nested within one another, from the whole biosphere,
down through its major ecosystem types (biomes), to local and possibly
short-lived associations of organisms. Second, the human influence on
ecosystems is globally pervasive. Humans are regarded as an integral,
rather than separate, part of social-ecological systems (Gunderson and
Holling, 2001; Berkes et al., 2003). Ecosystems are connected across
boundaries through the movement of energy, materials, and organisms,
and subsidies between terrestrial and freshwater systems are known
to be particularly important (Polis et al., 1997; Loreau et al., 2003). As
a consequence, human activities in terrestrial systems can significantly
impact freshwater ecosystems and their biota (Allan, 2004). The dynamics
of socio-ecological systems are governed not only by biophysical
processes such as energy flows, material cycles, competition, and
predation, but also by social processes such as economics, politics,
culture, and individual preferences (Walker and Salt, 2006). Third,
ecologists do not view ecosystems as necessarily inherently static and
at equilibrium in the absence of a human disturbance (Hastings, 2004).
Ecosystems vary over time and space in the relative magnitude of their
components and fluxes, even under a constant environment, owing to
internal dynamics (Scheffer, 2009). Furthermore, attempts to restrict
this intrinsic variation—or that resulting from externally generated
disturbances—are frequently futile, and may damage the capacity of
the ecosystem to adapt to a changing environment (Folke et al.,
2004). This contrasts with the popular view that ecosystems exhibit a
“balance of Nature” and benefit from being completely protected from
disturbance.
4.2.1. Ecosystems, Adaptation, Thresholds,
and Tipping Points
The term “adaptation” has different meanings in climate policy, ecology,
and evolutionary biology. In climate policy (see Glossary) it implies
human actions intended to reduce negative outcomes. In ecology,
ecosystems are said to be adaptive because their composition or function
can change in response to a changing environment, without necessarily
involving deliberate human actions (see Section 4.4.1). In evolutionary
biology, adaptation means a change in the genetic properties of a
population of individuals as a result of natural selection (Section 4.4.1.2),
a possibility seen since the Fourth Assessment Report as increasingly
relevant to climate change.
The notion of thresholds has become a prominent ecological and political
concern (Knapp, A.K. et al., 2008; Lenton et al., 2008; Leadley et al.,
2010). To avoid policy confusion, three types of threshold need to be
distinguished. The first reflects a human preference that the ecosystem
stays within certain bounds, such as above a certain forest cover. These
can be, by definition, negotiated. The second type reflects fundamental
biological or physical properties, for instance the temperature at which
frozen soils thaw (see Box 4-4) or the physiological tolerance limits of
species. The third type is caused by system dynamics: the point at which
the net effect of all the positive and negative feedback loops regulating
the system is sufficiently large and positive that a small transgression
becomes sufficiently amplified to lead to a change in ecosystem state
called a regime shift (Lenton et al., 2008). The new state exhibits different
dynamics, mean composition, sensitivity to environmental drivers, and
flows of ecosystem services relative to the prior state. This type of
threshold is called a “tipping point” (defined in the Glossary as a level
of change in system properties beyond which a system reorganizes,
often abruptly, and persists in its new state even if the drivers of the
change are abated ) and is important in the context of climate change
because its onset may be abrupt, hard to predict precisely, and effectively
irreversible (Scheffer et al., 2009; Leadley et al., 2010; Barnosky et al.,
2012; Brook et al., 2013; Hughes et al., 2013). Many examples of tipping
points have now been identified (Scheffer, 2009). Regional-scale
ecosystem tipping points have not occurred in the recent past, but there
is good evidence for tipping points in the distant past (Section 4.2.3)
and there is concern that they could occur in the near future (see Boxes
4-3 and 4-4).
The early detection and prediction of ecosystem thresholds, particularly
tipping points, is an area of active research. There are indications (Scheffer,
2009) that an increase in ecosystem variability signals the impending
approach of a threshold. In practice, such signals may not be detectable
against background noise and uncertainty until the threshold is crossed
(Biggs et al., 2009). The dynamics of ecosystems are complex and our
present level of knowledge is inadequate to predict all ecosystem
outcomes with confidence, even if the future climate were precisely
known.
Field observations over the past century in numerous locations in boreal,
temperate, and tropical ecosystems have detected biome shifts, the
replacement at a location of one suite of species by another (high
confidence). The effect is usually of biomes moving upward in elevation
and to higher latitudes (Gonzalez et al., 2010; see Figure 4-1). These shifts
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4
have often been attributed to anthropogenic climate change, as biome
distribution is known to broadly reflect climate zones, and the shifts have
been observed in areas without major human disturbance (medium
confidence; see Table 4-1). Projections of future vegetation distribution
under climate change indicate that many biomes could shift substantially,
including in areas where ecosystems are largely undisturbed by direct
human land use (Figure 4-2). The extent of the shift increases with
increasing global mean warming, without a sudden threshold (Scholze
et al., 2006; Pereira et al., 2010; Rehfeldt et al., 2012).
4.2.2. Methods and Models Used
Analysis of the current and past impacts of climate change on terrestrial
and freshwater ecosystems and their projection into the future relies
on three general approaches: inference from analogous situations in
the past or elsewhere in the present; manipulative experimentation,
deliberately altering one of a few factors at a time; and models with a
mechanistic or statistical basis. Studies of the relatively distant past
are discussed in depth in Section 4.2.3. Inferences from present spatial
patterns in relation to climate is at the core of climate envelope niche
modeling, a well-established but limited statistical technique for making
projections of the future distribution under equilibrium conditions (Elith
and Leathwick, 2009). Representing the rate of change during the non-
equilibrium conditions that will prevail over the next century requires a
more mechanistic approach, of which there are some examples (e.g.,
Keith et al., 2008; Kearney and Porter, 2009). Changes in ecosystem
function are usually determined by experimentation (see examples in
Section 4.3.3) and are modeled using mechanistic models, in many
cases with relatively high uncertainty (Seppelt et al., 2011).
4.2.3. Paleoecological Evidence
Paleoclimatic observations and modeling indicate that the Earths climate
has always changed on a wide range of time scales. In many cases,
particularly over the last million years, it has changed in ways that are
well understood in terms of both patterns and causes (Jansen et al.,
2007; see WGI AR5 Chapter 5). Paleoecological records demonstrate with
high confidence that the planet’s biota (both terrestrial and aquatic),
DE: Desert
RW: Tropical woodland
RD: Tropical deciduous broadleaf forest
Biomes
IC: Ice
BC: Boreal conifer forest
UA: Tundra and alpine
TC: Temperate conifer forest
TB: Temperate broadleaf forest
TM: Temperate mixed forest
TS: Temperate shrubland
TG: Temperate grassland
RG: Tropical grassland
RE: Tropical evergreen broadleaf forest
1-22: See Table 4-1
1
2
3
4
7
9
21
6
5
13
18
12
20
17
19
22
8
15
14
Figure 4-1 | Locations of observed biome shifts during the 20th century, listed in Table 4-1, derived from Gonzalez et al. (2010). The color of each semicircle indicates the
retracting biome (top for North America, Europe, Asia; bottom for Africa and New Zealand) and the expanding biome (bottom for North America, Europe, Asia; top for Africa and
New Zealand), according to published field observations. Biomes, from poles to equator: ice (IC), tundra and alpine (UA), boreal conifer forest (BC), temperate conifer forest (TC),
temperate broadleaf forest (TB), temperate mixed forest (TM), temperate shrubland (TS), temperate grassland (TG), desert (DE), tropical grassland (RG), tropical woodland (RW),
tropical deciduous broadleaf forest (RD), tropical evergreen broadleaf forest (RE). The background is the potential biome according to the MC1 dynamic global vegetation model
under the 1961–1990 climate. No shift was observed on locations 10, 11, 16, and 23 (see Table 4-1).
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Chapter 4 Terrestrial and Inland Water Systems
4
carbon cycle, and associated feedbacks and services have responded to
this climatic change, particularly when the climatic change was as large
as that projected during the 21st century under mid- to high-end radiative
forcing pathways (e.g., MacDonald et al., 2008; Claussen, 2009; Arneth
et al., 2010; Dawson et al., 2011; Willis and MacDonald, 2011). Excellent
examples of past large climate change events that drove large ecological
change, as well as recovery periods in excess of a million years, include
the events that led to the Earth’s five mass extinctions in the distant past
(i.e., during the Ordovician, about 443 Ma, the Devonian, about 359 Ma,
the Permian, about 251 Ma, the Triassic, about 200 Ma, and the
Cretaceous, about 65 Ma; Barnosky et al., 2011). Major ecological
change was also driven by climate change during the Paleocene-Eocene
Thermal Maximum (PETM, 56 Ma; Wing et al., 2005; Jaramillo et al., 2010;
Wing and Currano, 2013), the early Eocene Climatic Optimum (EECO, 53
to 50 Ma; Woodburne et al., 2009), the Pliocene (5.3 to 2.6 Ma; Haywood
and Valdes, 2006; Haywood et al., 2011), and the Last Glacial Maximum
(LGM) to Holocene transition between 21 and 6 ka (MacDonald et al.,
2008; Clark et al., 2009; Gill et al., 2009; Williams, J.W. et al., 2010;
Prentice et al., 2011; Daniau et al., 2012). The paleoecological record thus
provides high confidence that large global climate change, comparable
in magnitude to that projected for the 21st century, can result in large
ecological changes, including large-scale biome shifts, reshuffling of
communities, and species extinctions.
Rapid, regional warming before and after the Younger Dryas cooling
event (11.7 to 12.9 ka) provides a relatively recent analogy for climate
change at a rate approaching, for many regions, that projected for the
21st century for all Representative Concentration Pathways (RCPs; Alley
et al., 2003; Steffensen et al., 2008). Ecosystems and species responded
rapidly during the Younger Dryas by shifting distributions and abundances,
and there were some notable large animal extinctions, probably
exacerbated by human activities (Gill et al., 2009; Dawson et al., 2011).
In some regions, species became locally or regionally extinct (extirpated),
but there is no evidence for climate-driven global-scale extinctions
during this period (Botkin et al., 2007; Willis, K.J. et al., 2010). However,
the Younger Dryas climate changes differ from those projected for the
future because they were regional rather than global; may have only
regionally exceeded rates of warming projected for the future; and
started from a baseline substantially colder than present (Alley et al.,
2003). The mid-Holocene, about 6 ka, provides a very recent example
of the effects of modest climate change. Regional mean warming during
this period (mean annual temperature about 0.5°C to 1.0°C above
Location Reference Plots
Time
period
Shift
type
Retracting
biome
Expanding
biome
Temp. change
(ºC century
1
)
Precip. change
(% century
1
)
1. Alaska Range, Alaska, USA Lloyd and Fastie (2003) 18 1800 2000 L UA BC 1.1* 3
2
. Baltic Coast, Sweden Walther et al. (2005) 71944 2003 L
T
C TB
0
.6* 8
3
. Becca di Viou, Italy Leonelli et al. (2011) 11700 2008 E UA
B
C
0
.9* 6
4. Garibaldi, British Columbia, Canada Brink (1959) 1 1860 1959 E UA
BC 0.7* 16*
5
. Goulet Sector, Québec, Canada Payette and Filion (1985) 21880 1980 E UA
B
C
1
.4* 19*
6. Green Mountains, Vermont, USA Beckage et al. (2008) 33 1962 2005 E
BC TB 1.6* 6
7
. Jasper, Alberta, Canada Luckman and Kavanagh (2000) 1 1700 1994 E UA
B
C
0
.6 21*
8. Kenai Mountains, Alaska, USA Dial et al. (2007) 319511996E UA
BC 0.7 6
9. Kluane Range, Yukon, Canada Danby and Hik (2007) 2 1800 2000 E UA
BC 0.7 5
1
0. Low Peninsula, Québec, Canada Payette and Filion (1985) 11750 1980 N— 1.4* 19*
11. Mackenzie Mountains, Northwest
T
erritories, Canada
Szeicz and Macdonald (1995) 13 1700 1990 N— 1.4* 3
12. Montseny Mountains, Catalonia, Spain Peñuelas and Boada (2003) 50 1945 2001 E UA
TB 1.2* 3
1
3. Napaktok Bay, Labrador, Canada Payette (2007) 21750 2000 L UA
B
C
1
.1* 5
14. Noatak, Alaska, USA Suarez et al. (1999) 18 1700 1990 L UA
BC 0.6 19*
15. Putorana Mountains, Russian Federation Kirdyanov et al. (2012) 10 1500 2000 E UA
BC 0.3 10
16. Rahu Saddle, New Zealand Cullen et al. (2001) 71700 2000 N— 0.6* 3
17. Rai-Iz, Urals, Russian Federation Devi et al. (2008) 144 1700 2002 E UA
BC 0.3 35*
18. Sahel, Sudan, Guinea zones; Senegal Gonzalez (2001) 135 1945 1993 L RW RG 0.4* 48*
19. Sahel, Burkina Faso, Chad, Mali, Mauritania,
Niger
Gonzalez et al. (2012) 14 1960 2000 L RW RG 0.01* to 0.8* 31* to 9
20. Scandes, Sweden Kullman and Öberg (2009) 123 1915 2007 E UA
BC 0.8* 25*
21. Sierra Nevada, California, USA Millar et al. (2004) 10 1880 2002 E UA
TC 0.1 21*
22. South Island, New Zealand Wardle and Coleman (1992) 22 1980 1990 E TS
TB 0.6* 3
23. Yambarran, Northern Territory, Australia Sharp and Bowman (2004) 33 1948 2000 N— 0.06 35*
Table 4-1 | Biome shifts of the 20th century from published fi eld research that examined trends over periods >30years for biomes in areas where climate (rather than land use
change or other factors) predominantly infl uenced vegetation, derived from a systematic analysis of published studies (Gonzalez et al., 2010). Pre-AR4 publications are included
to provide a comprehensive review. Shift type: elevational (E), latitudinal (L), examined but not detected (N). The biome abbreviations match those in Figure 4-1. Rate of change
in temperature (Temp.) and fractional rate of change in precipitation (Precip.) are derived from linear least squares regression of 1901– 2002 data (Mitchell and Jones, 2005;
Gonzalez et al., 2010). The table provides general regional climate trends at 50 km spatial resolution because the references do not give uniform site-specifi c climate data to
compare across locations. The regional trends are consistent with local trends reported in each reference. *Rate signifi cant at P ≤ 0.05.
281
Terrestrial and Inland Water Systems Chapter 4
4
(d) Model agreement on climate change-driven biome shift between 1990 and 2100
RCP2.6 land use scenario (IMAGE model)
(a)
(c) RCP6.0 land use scenario (AIM model)
Projected primary vegetation cover in 2100
Primary vegetation cover in 2005
Percent of model agreement
P
ercent of primary vegetation*
c
over in grid cell
(b)
Comparison of panels (a), (b) and (c)
shows the effect of direct
human-induced vegetation change
through land use, without the effects
of climate change
biome shift is
projected to occur
due to climate
change
=
previously undisturbed
by human activities
no primary vegetation
*
Primary
vegetation
100
0
50
0
20
40
60
80
100
Figure 4-2 | Projections of climate change-driven biome shifts in the context of direct human land use. (a) Fraction of land covered by primary vegetation in 2005 (Hurtt et al.,
2011); (b) Fraction of land covered by primary vegetation in 2100 under the RCP2.6 land use scenario, with no effect of climate change (Hurtt et al., 2011); (c) Fraction of land
covered by primary vegetation in 2100 under the RCP6.0 land use scenario, with no effect of climate change (Hurtt et al., 2011). (d) Fraction of simulations showing climate
change-driven biome shift for any level of global warming between 1990 and 2100, with no direct anthropogenic land use change, using the MC1 vegetation model under 9
CMIP3 climate projections (3 GCMs, each forced by the SRES A2, A1B, and B1 scenarios; Gonzalez et al., 2010); Comparison of colored areas in (d) with those in (a) shows
where climate-driven biome shifts would occur in current areas of primary vegetation. Comparison of (b) and (c) with (a) illustrates two scenarios of how primary vegetation
could change due to direct human land use, irrespective of the effects of climate change. (b) shows the land use scenario associated with RCP2.6, in which global climate
change is projected to be smaller than that driving the biome shifts in (d) as a result of miti