Order Code RS22597
Updated May 15, 2008
Global Climate Change and Wildlife
Pervaze A. Sheikh
Analyst in Natural Resources and Environmental Policy
Resources, Science, and Industry Division
M. Lynne Corn, Jane A. Leggett, and Peter Folger
Specialists in Natural Resources and Environmental Policy
Resources, Science, and Industry Division
Recently projected climate changes could have widespread effects on wildlife
species. These effects might be positive or negative, depending on the species. Some
effects might include extinction, range shifts, mismatches in phenology (timing of
pollination, flowering, etc.), and population changes. Effects of climate change on
wildlife have been reported for some species and populations in localized areas. Many
scientists contend that climate change acts in concert with other variables (such as
habitat) to affect species. If the effects of climate change are widespread, there is
uncertainty on how wildlife will adapt. Some suggest that evolution and migration will
enable species to adapt, whereas others contend that adaptation will be minimal because
of limited habitat, and changes in climate that may occur more rapidly than adaptation
Climate change can have major repercussions for ecological systems, as indicated
by past major climate shifts. Effects of climate change are sometimes local, although
some may be widespread and linked to changes in other regions through food chains,
nutrient flows, and atmospheric and ocean circulation, among other things. Some
populations and species could flourish as the environment changes, whereas others could
decline. Some species would probably be able to adapt or adjust their ranges to stay
within a hospitable habitat. Others may be affected by obstacles to migration, disruptions
in food chains, or habitat alteration or loss.
Wildlife species can be affected by several climatic variables such as increasing
temperatures, changes in precipitation, and extreme weather events. Some scientists
predict that climate change can cause extinctions, which would lower biodiversity. Other
scientists contend that many species could benefit from climate change, such as some
migratory bird species which may have shorter distances to migrate for breeding and overwintering.1
The impacts of regional climate change and extreme weather on wild species has
been studied for several decades.2 Paleoclimatic studies have shown that species have
adjusted to climate changes at times in the past without mass extinctions.3 Yet, it is
uncertain if projected climate change widely foreseen today would mimic climate change
events in the geological record, and if human-ecosystem relationships would help or hurt
adaptation. In the last ten years, scientists have documented the effects of climate change
on species and populations on every continent and in most taxonomic groups.4 Some
studies provide correlations between climate change and species changes, others predict
changes with climate and species models, and some demonstrate mechanistic connections
between species changes and climate change.5 Many studies report that climate change
acts in concert with other factors to affect species and their habitat. For this reason, and
because of differences across biomes and species, it is difficult to generalize about the
overall impacts of climate change on biodiversity, wildlife, and ecosystems.
In discussing the effects of climate change on wildlife, some contend that climate
change might not be bad for species overall, even if some go extinct. They reason that
because biodiversity is greatest in tropical zones, biodiversity may benefit by warming
and greater precipitation. Further, they argue that climate change may induce species to
evolve behaviors or traits that will allow them to adapt to different conditions.6 Others
counter these arguments by stating that climate change might be too rapid for species to
evolve. Further, some contend that opportunities for species to adapt to climate change
might be limited due to habitat loss and fragmentation.
Scientific studies show that climate change affects species in different ways, yet the
message that these studies convey may be biased because studies that show no changes
in species due to climate change are less likely to be published.7 With monitoring,
research, and modeling, the responses of populations, species, landscapes and ecosystems
to climate change may be predicted more reliably, but the complexity of living systems
and the lack of long-term data make this task difficult.
R.A. Robinson, et al. Climate Change and Migratory Species, British Trust for Ornithology
(Norfolk, UK: 2005), 304 p.
Camille Parmesan, “Ecological and Evolutionary Responses to Recent Climate Change,”
Annual Review of Ecology, Evolution, and Systematics, vol. 37 (2006): 637-669. Hereafter
referred to as Parmesan 2006.
Isabel P. Montanez, et al., “CO2-Forced Climate and Vegetation Instability During Late
Paleozoic Deglaciation,” Science, vol. 315, no. 5808 (2007): 87-91.
T. Root, et al., Fingerprints of Global Warming on Wild Animals and Plants, Nature, vol.
A.C. Baker et al., Corals Adaptive Response to Climate Change, Nature, vol. 430 (2004): p.
See Parmesan 2006 for a discussion on this issue.
Climate Change Affecting Wildlife
Climate change producing higher temperatures may affect wildlife by causing
species to expand, contract, or shift their ranges, typically toward the poles or higher
elevations.8 It may alter their phenologies,9 leading to mismatches with their food and
habitat resources. It may also cause habitat loss, and allow exposure to new pathogens.
These changes could have either negative or positive effects on the abilities of species to
survive. The abilities of species to adapt to some degree of climate change depends, in
part, upon the rate at which the change occurs. The following sections of this report
provide examples of wildlife that are thought to be, in part, affected by climate change.
Examples were taken from published studies with appropriate citations. The examples
illustrate the types of changes that have been observed.
Range Shifts. There are few studies that report the effects of climate change over
an entire species’ range, partly because of the difficulties of gathering data throughout a
range during a period long enough to produce significant results.10 Even so, range shifts
have been documented in some species of birds and insects, and in some marine
communities. One example is the mountain pine beetle (Dendroctonus ponderosae). The
mountain pine beetle feeds primarily on lodgepole pine,11 and occasionally on other
species including whitebark pine (Pinus albicaulis).12 Until recent decades, the beetle has
been held in check at higher elevations by its inability to complete a full life cycle due to
cold temperatures and a short growing season. Research shows that warmer temperatures
during winter allow beetles to complete a full reproductive cycle within one year in
whitebark pine habitat.13 As a result, they can time their breeding cycle to produce huge
numbers of eggs whose emerging larvae can overwhelm the defenses not only of damaged
trees but also of healthy ones. Studies show that the expansion of beetle populations
correlates closely with local warming data. Beetle populations are reported to be moving
up mountains, and northward into Canada where they are occupying some forest stands
for the first time in recorded history.
L. Hannah, T. E. Lovejoy, and S. H. Schneider, “Biodiversity and Climate Change in Context,”
in Climate Change and Biodiversity, T.E. Lovejoy and L. Hannah, eds. (Yale University Press,
New Haven CT: 2005): 3-14.
Phenology is “the relationship between climate and periodic natural phenomena such as the
migration of birds, bud bursting, or the flowering of plants.” The Dictionary of Ecology and
Environmental Science, H. W. Hart, ed. (New York, NY: Henry Holt & Co, 1993)
The lodgepole pine is adapted to this beetle, and stands of this fast-growing tree can regenerate
fairly quickly — for trees.
The heavy seed crop of the whitebark pine supports many species, including the Clark’s
nutcracker which harvests and stores large caches of the seeds, and feeds on them through winter
and into the breeding season. Red squirrels also collect and store the seeds. The stored caches
are important fall and spring food sources for grizzlies.
This discussion is adapted from Michel Nijhuis, “Global Warming’s Unlikely Harbingers,”
High Country News, vol 36 (July 19, 2004): p. 1. The author cites a variety of primary sources,
largely U.S. Forest Service scientists.
Phenological Changes. Phenological cues are critical in the life cycles of many
species. When global warming alters the climate, certain phenological events generally
shift accordingly. If a phenological change in one species does not match linked changes
in an interdependent species, an ecological mismatch can occur.14 For example, if certain
trees bloom earlier in response to warmer springs, but pollinators do not hatch earlier,
disruptions (e.g., failed or inadequate pollination) may occur. Mismatches can occur
between predators and prey, herbivorous insects and host plants, and pollinators and
flowering plants, among others. Scientists are studying potential mismatches caused by
climate change because they can disrupt the reproductive cycle of many species. In one
example, variability in precipitation, linked to regional climate change, is considered as
the cause of the extinction of two populations of checkerspot butterflies in California.15
Changing levels of precipitation were found to alter the relationship between butterfly
larvae and host plants. In very wet or dry years, larvae do not get the opportunity to feed
on host plants before the plants die. These lost opportunities for successful reproduction
cause declines in butterfly abundance, which eventually may lead to their extinction.
Population Decline Due to Habitat Loss. There are few examples of studies
that directly associate wildlife population declines with climate change. Indirect links
have been reported, such as population declines in species due to habitat loss exacerbated
by climate change. For example, the impact of climate change on Antarctic krill (small,
shrimp-like animals) has been documented. Antarctic krill are major grazers in the
Southern Atlantic Ocean and are food for various species of fish targeted by commercial
fisheries. Declines in sea-ice area and in the duration of sea-ice formation, linked in part
to climate change in Antarctica, have been connected to declines in krill density.
Variability in krill densities has implications for the Antarctic food web, which includes
penguins, albatrosses, seals, and whales.16 Another example is polar bears, which are
declining due to seasonal reductions in ice cover. Reductions in ice cover are linked to
a warmer climate in the Arctic.
Pathogens. Some pathogens could increase their ranges due to climate change,
whereas others may diminish their ranges. For example, harlequin frogs are declining due
to increased outbreaks of a harmful chytrid fungus. In the last 20 years, 67% of the 110
species of harlequin frogs have gone extinct.17 A mechanistic explanation of how climate
change promotes outbreaks of the chytrid fungus has been presented. Nighttime
temperatures are shifting closer to the thermal optimum for chytrid growth, and daytime
cloudiness prevents frogs from seeking thermal refuges.18 These climatic shifts are
promoting outbreaks of chytrid fungus in areas where harlequin frog populations reside.
Marcel Visser and Christiaan Both, “Shifts in Phenology Due to Global Climate Change: The
Need for a Yardstick,” Proceedings of the Royal Society Bulletin, vol. 272 (2005): 2561-2569.
John McLaughlin, et al., “Climate Change Hastens Population Extinctions,” Proceedings of
the National Academy of Sciences, vol. 99, no. 9 (2002): 6070-6074.
Angus Atkinson, et al., “Long-term decline in krill stock and increase in salps within the
Southern Ocean, Nature,” vol. 432 (2004): 100-103.
J. Alan Pounds, et al., “Widespread Amphibian Extinctions from Epidemic Disease Driven by
Global Warming,” Nature, vol. 439 (2006): 161-167.
Andrew Blaustein and Andy Dobson, “A Message from the Frogs,” Nature vol. 439 (2006):
Wildlife Adaptation to Climate Change
Species and populations have demonstrated that they can adapt in a variety of ways
to some degree of climate change. For example, they can shift their ranges, change their
phenologies, and with sufficient time, may adapt to climate change through evolution.
Paleoclimate evidence indicates that some ecosystems restructured during some past
climate changes without records of mass extinctions.19 Assessing the ability of species
to adapt to climate change is difficult because other stressors that may drive adaptation
could be present, such as habitat loss due to factors other than climate change,
competition from other species, and invasive species. Further signs of adaptation, such
as range expansions or shifts in phenology, may initially be viewed as positive responses
by a species to climate changes, but have negative consequences if these shifts do not
correspond to other ecosystem properties or other necessary conditions needed for that
species’ survival. For example, if the natural response to climate change for a species
would be to expand northward, the consequences might be severe if intervening
developed areas replace suitable habitat or block access to it.
The rate of climate change reported in this century is generally seen as being
uncharacteristically rapid and many scientists have questions concerning how or whether
species will adapt. Climate change models based on global average temperature changes
are less precise about local climate changes that could be important for many species.
This uncertainty has led some to propose artificial methods of adaptation such as assisted
migration, which is the collection and transport of species from unsuitable to suitable
habitat. This technique has been used with mixed results with endangered species and
many question its viability and cost. Other suggestions to assist adaptation of wildlife
include building corridors between protected areas to give species paths to migrate and
shift their ranges.
Climate change has the potential to adversely affect species. Some contend that
effects from recently projected climate change will warrant mitigation of effects to
wildlife and that planning for mitigation is prudent now. Others assert that the effects of
climate change on species may not need intervention and that many species may be able
to adapt successfully. Addressing this issue may require answering several questions that
are still being discussed. For example, will the rate of any climate change be slow enough
to allow species to adapt? What are local changes in climate that would affect specific
populations and ecosystems? How could human development and management of natural
resources interact with the natural adaptation process of species under climate change?
And, is the extinction of species due to climate change a concern or a natural process?
If the effects of climate change on wildlife are widespread and occur rapidly, there
are resulting legislative implications. Several wildlife laws and management plans that
have been developed with an understanding of the life history, distribution, and habitat
needs of species may merit assessment to see if they function as desired under projected
T.E. Lovejoy and L. Hannah, “Global Greenhouse Gas Levels and the Future of Biodiversity,”
in Climate Change and Biodiversity, T.E. Lovejoy and L. Hannah eds. (Yale University Press,
New Haven CT: 2005): 387-395.
climate change. For example, under the Endangered Species Act (ESA), critical habitat
designation, habitat conservation plans, and biological opinions for several species might
have to be re-done if data on species change. This could overwhelm scientific resources
and agency resources to review new data. For aquatic species, changes in their habitat
requirements could require water flows and water supply to be altered in river
management plans. This possibility is tempered by some who contend that changes to
species may be gradual enough that wildlife laws that address potential changes may be
sufficient. In the case of ESA, there are provisions that require the revision of recovery
plans or conservation plans if new scientific data are presented.
The control, eradication, and prevention of invasive and pest species are generally
addressed on a species-by-species basis in management plans. If rapid climate change
affects pest or exotic species, scientific knowledge may not keep pace. Further, changes
in species ranges may make it difficult to determine if species are exotic or native species
with new ranges. Separating exotic species from adapting species may be relevant for
national park and refuge managers. Managers might be faced with challenging
management objectives: whether to preserve and protect current wildlife species and
facilitate the adaptation of new species into protected areas.20
The effects of climate change on wildlife are being viewed by some as an issue
within the larger context of potential changes to ecosystems. Ecological factors that affect
wildlife, including water flows and availability, soils, and nutrients, can be addressed in
an ecosystem context. Consequently, large-scale ecosystem restoration initiatives might
have to incorporate changes in their restoration plans to address the potential effects of
climate change. Restoration plan horizons generally range from 20 to 50 years over which
local climate may change substantially. For example, the restoration of the Everglades
ecosystem is expected to take 30 years under the Comprehensive Everglades Restoration
Plan. This plan could need to be revised if recently predicted sea level rise occurs and
causes changes in water flow in the Everglades.21
D. Scott, “Integrating Climate Change into Canada’s National Park System,” in Climate
Change and Biodiversity, T.E. Lovejoy and L. Hannah eds. (Yale University Press, New Haven
CT: 2005): 342-345.
Some restoration plans include adaptive management, which incorporates information from
new or unforeseen circumstances into a project to assure that the goals of the project are achieved
efficiently. It is unclear if adaptive management will allow for large-scale changes in plans that
may happen under climate change.