Global Climate Change and Wildlife

^Pr^ep^ar^{ed f}^o^r^M^e^m^b^ers^an^d^Com^mⁱ^t^t^ees^of^C^ong^r^e^ss

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
can respond.

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 ¹
distances to migrate for breeding and over-wintering.
The impacts of regional climate change and extreme weather on wild species has been studied for ²
several decades. Paleoclimatic studies have shown that species have adjusted to climate changes ³
at times in the past without mass extinctions. 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 ⁴
most taxonomic groups. Some studies provide correlations between climate change and species
changes, others predict changes with climate and species models, and some demonstrate ⁵
mechanistic connections between species changes and climate change. 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 ⁶
them to adapt to different conditions. 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.

¹^R^.^A^.^R^obins^on,^e^t^a^l^.^C^l^im^ate^C^h^ange^an^{d M}ⁱ^gr^ator^y^Spe^cⁱ^e^s^{, B}^r^iti^s^h^T^r^us^{t f}^o^r^O^r^nith^ol^og^y⁽^N^or^f^o^{lk, U}^K^:²⁰⁰⁵⁾^,³⁰⁴
^p.
²^Ca^m^ille^P^a^rm^e^s^aⁿ^{, “}^E^c^o^logⁱ^c^a^l^a^{nd Ev}^o^l^uti^ona^ry^Re^s^pons^e^s^{to Re}^c^eⁿ^{t Clim}^a^t^e^Chaⁿ^g^e^,”^Annua^{l Re}^vⁱ^e^w^{of Ec}^ol^ogy^,
^Ev^oluti^oⁿ^,^aⁿ^d^Sy^s^t^e^m^atic^s^{, v}^o^l^.³⁷⁽²⁰⁰⁶⁾^:⁶³^7-⁶^69.^H^e^r^e^a^f^te^r^r^e^f^e^r^r^e^{d to a}^s^P^a^r^m^e^s^{an 20}^06.
³^Isab^el^P^.^Mo^nt^an^ez,^et^al^.^,^“CO²^-Forc^e^d^Clim^a^t^e^a^nd^V^e^g^e^ta^{tion In}^sta^b^ility^During^L^a^te^P^a^le^oz^oic^D^e^g^l^a^cⁱ^a^tion,”
^Sc^ie^nc^e^{, v}^o^l.³¹^5,^no.⁵⁸⁰⁸⁽²⁰⁰⁷⁾^{: 87-}⁹¹^.
⁴^Par^m^e^s^{an 20}⁰⁶^.
⁵^T^.^R^oot,^e^t^a^l^.,^Fing^e^r^prⁱⁿ^ts^of^G^l^oba^{l W}^a^r^m^ing^{on W}^{ild A}ⁿ^im^a^l^s^and^Plaⁿ^ts^,^Na^t^u^r^e^,^v^o^l.⁴²¹⁽²⁰⁰³⁾^:^57-⁶⁰^.
⁶^A^.^C^.^B^a^k^e^r^e^t^a^l^{., C}^o^r^a^ls^A^d^a^p^tive^R^e^s^pons^e^to^C^lim^a^t^e^C^h^aⁿ^g^e^,^Na^tu^re^,^vo^l.⁴³^{0 (}²⁰⁰⁴⁾^:^p^.⁷⁴^1.

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 ⁷
climate change are less likely to be published. 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.
Climate change producing higher temperatures may affect wildlife by causing species to expand, ⁸
contract, or shift their ranges, typically toward the poles or higher elevations. It may alter their ⁹
phenologies, 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.
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 ¹⁰
produce significant results. 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 ¹¹
(Dendroctonus ponderosae). The mountain pine beetle feeds primarily on lodgepole pine, and ¹²
occasionally on other species including whitebark pine (Pinus albicaulis). 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 ¹³
pine habitat. 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

⁷^S^ee^Par^m^e^s^{an 20}⁰⁶^f^o^r^a^dis^c^us^sⁱ^on^on^this^is^s^u^e^.
⁸^L^.^H^a^nna^{h, T}^.^E.^L^o^v^e^joy^,^a^{nd S.}^H^.^Sc^hⁿ^eⁱ^de^r^,^“^Bⁱ^odiv^e^r^s^ity^a^{nd C}^lim^a^t^e^C^h^aⁿ^g^e^{in C}^onte^x^t,”ⁱⁿ^C^lim^ate^C^h^an^ge
^and^Bi^odiv^e^r^s^ity^{, T}^.^{E. L}^o^v^e^joy^aⁿ^{d L}^.^H^a^nna^h,^e^d^s^.⁽^Y^a^l^e^Uⁿ^iv^e^r^sⁱ^t^y^P^r^e^s^s^,^N^e^w^H^a^ve^{n C}^T^{: 200}⁵⁾^{: 3}^-^14.
⁹^Pheⁿ^olo^g^y^is^“^t^he^r^e^la^ti^ons^hip^be^tw^ee^{n c}^lim^a^t^e^a^{nd pe}^rⁱ^odic^na^tur^a^{l phe}^nom^eⁿ^a^s^u^c^h^a^s^the^mⁱ^g^r^a^{tion of}^bir^d^s^,^b^u^d
^bur^s^tⁱⁿ^g^,^or^the^f^l^ow^e^r^ing^of^plaⁿ^ts^.”^The^Dⁱ^c^tio^nar^y^{of Ec}^ol^ogy^an^{d Env}ⁱ^r^onm^eⁿ^t^a^l^Sc^ie^nc^e^{, H}^.^W^.^H^a^{rt, e}^d^{. (N}^e^w
^Yo^rk,^{NY: Hen}^r^y^Ho^{lt & Co}^,¹⁹⁹³⁾
¹⁰^Par^m^e^s^{an 20}⁰⁶^.
¹¹^T^h^e^lodg^e^pole^pi^ne^is^a^d^a^p^te^d^to^this^be^e^tle^{, a}^{nd s}^t^aⁿ^ds^of^this^f^a^s^t^-^g^r^o^wⁱ^ng^tr^e^e^c^aⁿ^r^e^g^e^ne^r^a^te^f^a^ir^l^y^quic^k^ly^—^f^or
^t^r^ees.
¹²^T^h^e^he^a^v^y^s^e^e^d^c^r^{op of}^the^w^h^ite^ba^r^k^pine^s^u^pp^or^ts^m^aⁿ^y^sp^eci^es,ⁱⁿ^cl^udⁱⁿ^{g t}^h^{e Cl}^{ark’s n}^u^t^{cracker w}^hⁱ^c^h^h^a^rvest^s
^an^d^st^o^r^{es l}^a^{rge cach}^{es o}^f^t^h^{e seed}^s,^and^f^eed^{s o}ⁿ^t^h^em^t^h^ro^u^g^h^wⁱⁿ^t^{er an}^{d i}ⁿ^t^o^t^h^{e b}^r^eedⁱⁿ^{g seaso}ⁿ^.^Red^sq^ui^rrel^s^al^so
^co^l^l^ect^an^d^st^o^r^{e t}^h^{e seed}^s.^T^h^{e st}^o^r^ed^cach^{es are i}^m^p^o^r^t^aⁿ^t^f^a^l^l^an^{d sp}^riⁿ^g^f^o^o^d^sou^r^{ces f}^o^{r gri}^zzlⁱ^e^s.
¹³^T^h^{is disc}^ussioⁿ^{is a}^d^a^p^te^{d f}^r^om^Mic^h^e^l^Nijh^{uis, “}^G^loba^{l W}^a^rmⁱⁿ^g^’^{s Unlik}^e^l^y^Ha^rbing^e^rs,”^Hⁱ^{gh C}^oun^tr^y^N^e^w^s^{, v}^o^l
^{36 (}^J^uly^{19, 2}⁰⁰⁴⁾^:^p.^{1. T}^h^e^a^u^t^h^or^c^ite^s^a^v^a^rⁱ^e^t^y^of^pr^im^a^r^y^s^our^c^e^s^{, la}^r^g^e^l^y^U^.^{S. For}^e^s^t^Se^r^v^ic^e^s^c^ie^ntis^ts^.

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.
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 ¹⁴
occur. 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 ¹⁵
extinction of two populations of checkerspot butterflies in California. 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.
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 ¹⁶
whales. 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.
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 ¹⁷
chytrid fungus. In the last 20 years, 67% of the 110 species of harlequin frogs have gone extinct.
A mechanistic explanation of how climate change promotes outbreaks of the chytrid fungus has

¹⁴^M^a^rcel^Vⁱ^{sser an}^{d Ch}^ri^stⁱ^{aan Bo}^t^h^,^“S^hi^f^t^{s i}ⁿ^P^h^en^o^l^o^g^y^Du^{e t}^o^G^l^o^b^a^l^Clⁱ^m^at^{e Ch}^an^ge:^T^h^{e Need}^fo^{r a Yard}^stⁱ^c^k,^”
^P^r^o^ceedⁱⁿ^g^s^o^f^t^h^e^R^o^ya^l^S^o^cⁱ^e^t^y^B^u^l^l^e^tⁱⁿ^,^v^o^l.²^{72 (}²⁰⁰⁵⁾^{: 2}⁵⁶¹^-²⁵⁶⁹^.
¹⁵^Jo^hn^M^c^L^a^u^g^h^lⁱⁿ^,^et^al^.^,^“Clⁱ^m^at^{e Ch}^an^{ge Hast}^en^{s P}^o^pu^l^a^tⁱ^oⁿ^E^x^tⁱⁿ^c^tⁱ^oⁿ^s^,^”^P^r^o^ceedⁱⁿ^g^s^o^f^t^h^{e Na}^tⁱ^oⁿ^a^l^A^c^ad^{emy o}^f
^Sc^ie^nc^e^s^,^v^o^{l. 9}⁹^,^no^{. 9}⁽²⁰⁰²⁾^:⁶⁰⁷⁰^-⁶⁰⁷^4.
¹⁶^Aⁿ^g^u^s^A^t^kⁱⁿ^s^oⁿ^,^{et al.}^,^“L^oⁿ^g^-term^d^eclin^{e in}^k^r^{ill sto}^c^k^an^dⁱⁿ^cre^a^{se in}^salp^{s w}^ithⁱⁿ^t^h^{e S}^o^u^t^h^e^rn^Ocean^,^Na^tu^re^,”
^v^o^{l. 4}^{32 (}²⁰⁰⁴⁾^{: 1}^00-¹⁰^3.
¹⁷^J^.^A^l^aⁿ^Pou^nds^,^e^t^a^l^{., “}^W^ide^s^pr^e^a^{d A}^m^phibiaⁿ^Ex^ti^nc^tio^ns^f^r^om^E^p^ide^m^ic^Dⁱ^s^e^a^s^e^D^r^iv^eⁿ^by^G^l^oba^{l W}^a^r^m^ing^,^”
^Na^tu^re,^v^o^l^.⁴³⁹⁽²⁰⁰⁶⁾^{: 1}^61-¹⁶^7.

been presented. Nighttime temperatures are shifting closer to the thermal optimum for chytrid ¹⁸
growth, and daytime cloudiness prevents frogs from seeking thermal refuges. These climatic
shifts are promoting outbreaks of chytrid fungus in areas where harlequin frog populations reside.
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 ¹⁹
mass extinctions. 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?

¹⁸^A^ndr^e^w^B^l^a^u^s^t^eⁱ^{n a}^{nd A}^ndy^D^obs^{on, “}^A^Me^s^s^a^g^e^f^r^o^m^the^Fr^og^s^,^”^Na^tu^re^v^o^l.⁴³^{9 (}²⁰⁰⁶⁾^:¹^43-¹⁴^4.
¹⁹^T^.^{E. L}^o^v^e^jo^y^a^{nd L}^.^H^a^nna^h,^“^G^loba^{l G}^r^e^e^nho^us^e^G^a^s^L^e^v^e^ls^a^{nd the}^F^u^tur^e^of^Bⁱ^odiv^e^r^s^ity^,”ⁱⁿ^C^lim^ate^C^h^an^ge
^and^Bi^odiv^e^r^s^ity^{, T}^.^{E. L}^o^v^e^joy^aⁿ^{d L}^.^H^a^nna^{h e}^d^s^.⁽^Y^a^l^e^Uⁿ^iv^e^r^s^ity^P^r^e^s^s^,^N^e^w^H^a^ve^{n C}^T^{: 200}⁵⁾^{: 3}^87-³⁹^5.

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 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 ²⁰
wildlife species and facilitate the adaptation of new species into protected areas.
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 ²¹
predicted sea level rise occurs and causes changes in water flow in the Everglades.
^P^e^rv^{aze A}^.^Sh^eⁱ^kh ^{M. Ly}ⁿⁿ^{e C}^o^rn
^Sp^{ecialist i}ⁿ^Nat^u^r^a^{l Reso}^u^r^{ces P}^o^licy^Sp^{ecialist i}ⁿ^Nat^u^r^a^{l Reso}^u^r^{ces P}^o^licy
^ps^h^eⁱ^k^h@^crs^.^l^o^c.g^o^v^,^7-⁶⁰⁷⁰^l^c^orn^@^crs^.^l^o^c.g^o^v^,^7-⁷²⁶⁷
^J^aⁿ^e^A^.^L^e^g^g^ett ^P^e^ter^Fo^lg^er
^Sp^{ecialist i}ⁿ^En^er^g^y^aⁿ^d^En^vⁱ^r^oⁿ^m^eⁿ^{tal P}^o^lic^y^Sp^{ecialist i}ⁿ^En^er^g^y^aⁿ^d^Natu^r^a^{l Reso}^u^r^{ces P}^o^lic^y
^j^a^leg^g^e^tt^@cr^s^.lo^c^.g^o^v^{, 7-}⁹⁵²⁵^pf^ol^g^e^r@^cr^s^.^l^o^c.g^o^v^,^7-¹⁵¹⁷

²⁰^{D. Sc}^ott^,^“^I^nte^g^ra^ting^Clim^a^t^e^Chaⁿ^g^e^into^Ca^na^da^{’s Na}^tio^na^l^P^a^r^k^Sy^ste^m^,”ⁱⁿ^C^lim^ate^C^h^an^ge^aⁿ^d^Bi^odiv^e^r^s^ity^,
^T^.^{E. L}^o^v^e^jo^y^a^{nd L}^.^H^a^nna^{h e}^d^s^.⁽^Y^a^l^e^Uⁿ^iv^e^r^sⁱ^t^y^P^r^e^s^s^,^N^e^w^H^a^ve^{n C}^T^{: 20}⁰⁵⁾^:³⁴^2-³⁴⁵^.
²¹^Som^e^r^e^s^t^or^a^tion^plaⁿ^sⁱⁿ^c^l^u^d^e^a^d^a^p^tiv^e^m^a^na^gem^e^{nt, w}^h^ic^{h inc}^o^r^por^a^t^e^s^inf^o^r^m^a^{tion f}^r^om^new^or^unf^or^e^s^e^eⁿ
^ci^rcu^m^st^an^{ces i}ⁿ^t^o^{a p}^r^o^j^ect^t^o^assu^{re t}^h^at^t^h^{e go}^al^{s o}^f^t^h^{e pro}^j^ect^a^r^{e ach}ⁱ^e^ved^e^f^fⁱ^ci^en^t^l^y^.^Itⁱ^s^uⁿ^c^l^{ear i}^f^ad^ap^tⁱ^v^e
^m^a^na^g^e^m^e^{nt w}^{ill a}^llow^f^o^{r la}^rg^e^-^sc^a^l^e^c^h^aⁿ^g^e^{s in pla}ⁿ^{s t}^h^a^t^m^a^y^h^a^ppeⁿ^un^de^{r c}^lim^a^t^e^c^h^aⁿ^g^e^.