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 Climate
Impacts on Ecosystems
Overview
Climate is an important environmental influence on
ecosystems. Changing climate affects ecosystems in a variety
of ways. For instance, warming may force species to migrate
to higher latitudes or higher elevations where temperatures
are more conducive to their survival. Similarly, as sea
level rises, saltwater intrusion into a freshwater system
may force some key species to relocate or die, thus removing
predators or prey that are critical in the existing food
chain.
Climate change not only affects ecosystems and species
directly, it also interacts with other human stressors such
as development. Although some stressors cause only minor
impacts when acting alone, their cumulative impact may lead
to dramatic ecological changes. For instance, climate change
may exacerbate the stress that land development places on
fragile coastal areas. Additionally, recently logged
forested areas may become vulnerable to erosion if climate
change leads to increases in heavy rain storms. |
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Changes in the Timing of Seasonal
Life Cycle Events
For many species, the climate where they live or spend part
of the year influences key stages of their annual life
cycle, such as migration, blooming, and reproduction. As
winters have become shorter and milder, the timing of these
events has changed in some parts of the country:
Earlier springs have led to earlier nesting for 28 migratory
bird species on the East Coast of the United States.
Northeastern birds that winter in the southern United States
are returning north in the spring 13 days earlier than they
did in a century ago.
In a California study, 16 out of 23 butterfly species
shifted their migration timing and arrived earlier.
Because species differ in their ability to adjust,
asynchronies can develop, increasing species and ecosystem
vulnerability. These asynchronies can include mismatches in
the timing of migration, breeding, pest avoidance, and food
availability. Growth and survival are reduced when migrants
arrive at a location before or after food sources are
present.
Range Shifts
As temperatures increase, the habitat ranges of many North
American species are moving north and to higher elevations.
In recent decades, in both land and aquatic environments,
plants and animals have moved to higher elevations at a
median rate of 36 feet (0.011 kilometers) per decade, and to
higher latitudes at a median rate of 10.5 miles (16.9
kilometers) per decade. While this means a range expansion
for some species, for others it means movement into less
hospitable habitat, increased competition, or range
reduction, with some species having nowhere to go because
they are already at the top of a mountain or at the northern
limit of land suitable for their habitat. These factors lead
to local extinctions of both plants and animals in some
areas. As a result, the ranges of vegetative biomes are
projected to change across 5-20% of the land in the United
States by 2100.
For example, boreal forests are invading tundra, reducing
habitat for the many unique species that depend on the
tundra ecosystem, such as caribou, arctic foxes, and snowy
owls. Other observed changes in the United States include a
shift in the temperate broadleaf/conifer forest boundary in
the Green Mountains of Vermont; a shift in the shrubland/conifer
forest boundary in New Mexico; and an upward elevation shift
of the temperate mixed/conifer forest boundary in Southern
California.
As rivers and streams warm, warmwater fish are expanding
into areas previously inhabited by coldwater species. As
waters warm, coldwater fish, including many highly-valued
trout and salmon species, are losing their habitat, with
projections of 47% habitat loss by 2080. In certain regions
in the western United States, losses of western trout
populations may exceed 60 percent, while in other regions,
losses of bull trout may reach about 90 percent. Range
shifts disturb the current state of the ecosystem and can
limit opportunities for fishing and hunting.
See the Agriculture and Food Supply Impacts page for
information about how habitats of marine species have
shifted northward as waters have warmed. |
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 Food
Web Disruptions
The impact of climate change on a particular species can
ripple through a food web and affect a wide range of other
organisms. For example, the figure below shows the complex
nature of the food web for polar bears. Not only is the
decline of sea ice impairing polar bear populations by
reducing the extent of their primary habitat, it is also
negatively impacting them via food web effects. Declines in
the duration and extent of sea ice in the Arctic leads to
declines in the abundance of ice algae, which thrive in
nutrient-rich pockets in the ice. These algae are eaten by
zooplankton, which are in turn eaten by Arctic cod, an
important food source for many marine mammals, including
seals. Seals are eaten by polar bears. Hence, declines in
ice algae can contribute to declines in polar bear
populations.
Picture - The Arctic
food web is complex. The loss of sea ice can ultimately
affect the entire food web, from algae and plankton to fish
to mammals. Source: NOAA (2011) |
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Buffer and Threshold Effects
Ecosystems can serve as natural buffers from extreme events
such as wildfires, flooding, and drought. Climate change and
human modification may restrict ecosystems’ ability to
temper the impacts of extreme conditions, and thus may
increase vulnerability to damage. Examples include reefs and
barrier islands that protect coastal ecosystems from storm
surges, wetland ecosystems that absorb floodwaters, and
cyclical wildfires that clear excess forest debris and
reduce the risk of dangerously large fires.
In some cases, ecosystem change occurs rapidly and
irreversibly because a threshold, or "tipping point," is
passed. One area of concern for thresholds is the Prairie
Pothole Region in the north-central part of the United
States. This ecosystem is a vast area of small, shallow
lakes, known as "prairie potholes" or "playa lakes." These
wetlands provide essential breeding habitat for most North
American waterfowl species. The pothole region has
experienced temporary droughts in the past. However, a
permanently warmer, drier future may lead to a threshold
change—a dramatic drop in the prairie potholes that host
waterfowl populations, which subsequently provide highly
valued hunting and wildlife viewing opportunities.
Similarly, when coral reefs become stressed from increased
ocean temperatures, they expel microorganisms that live
within their tissues and are essential to their health. This
is known as coral bleaching. As ocean temperatures warm and
the acidity of the ocean increases, bleaching and coral
die-offs are likely to become more frequent. Chronically
stressed coral reefs are less likely to recover.
Pathogens, Parasites, and Disease
Climate change and shifts in ecological conditions could
support the spread of pathogens, parasites, and diseases,
with potentially serious effects on human health,
agriculture, and fisheries. For example, the oyster
parasite, Perkinsus marinus, is capable of causing large
oyster die-offs. This parasite has extended its range
northward from Chesapeake Bay to Maine, a 310-mile expansion
tied to above-average winter temperatures. For more
information about climate change impacts on agriculture,
visit the Agriculture and Food Supply Impacts page. To learn
more about climate change impacts on human health, visit the
Health Impacts page. |
 Extinction Risks
Climate change, along with habitat destruction and
pollution, is one of the important stressors that can
contribute to species extinction. The IPCC estimates that
20-30% of the plant and animal species evaluated so far in
climate change studies are at risk of extinction if
temperatures reach the levels projected to occur by the end
of this century. Global rates of species extinctions are
likely to approach or exceed the upper limit of observed
natural rates of extinction in the fossil record. Examples
of species that are particularly climate sensitive and could
be at risk of significant losses include animals that are
adapted to mountain environments, such as the pika; animals
that are dependent on sea ice habitats, such as ringed seals
and polar bears; and coldwater fish, such as salmon in the
Pacific Northwest. |
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EPA Page |
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Key Points
Climate change is likely the leading factor decreasing the
populations and shifting habitat range of the American pika
(Ochotona princeps). Source: National Climate Assessment
(2009).
Climate change can alter where species live, how they
interact, and the timing of biological events, which could
fundamentally transform current ecosystems and food webs.
Climate change can overwhelm the capacity of ecosystems to
mitigate extreme events and disturbance, such as wildfires,
floods, and drought.
Mountain and arctic ecosystems and species are particularly
sensitive to climate change.
Projected warming could greatly increase the rate of species
extinctions, especially in sensitive regions.
Terminology
An ecosystem refers to the animals, plants, and
microorganisms that live in one place, as well as the
environmental conditions that support them.
Ecosystem services include the products and services
provided by ecosystems, such as food, fuel, timber, water,
clean air, and medicines. It also includes less material
benefits, such as regulation of local climate conditions and
aesthetic value or cultural identity.
An ecological threshold is the point at which there is an
abrupt change in an ecosystem quality, property, or
phenomenon, or where small changes in one or more external
conditions produce large and persistent responses in an
ecosystem.
A biome is a large, naturally occurring community of plants
and animals occurring in a regional or global land area.
A food web is a group of predators and prey that interact in
a habitat or ecosystem.
A stressor is a factor that reduces the health or
productivity of an ecosystem (i.e., causes stress).
The Pika
The American pika is a hamster-sized relative of the rabbit
that is found in the cold, mountainous of the western United
States. Because of their sensitivity to hot temperatures,
the warming climate is causing pika populations to die off
at elevations below 7,000 feet. Of 25 pika populations
studied in the Great Basin between the Rocky Mountains and
the Sierra Nevada, more than one third have disappeared in
the past few decades. However, because of their retreat to
colder climates, they are well-distributed in higher
elevations and are not endangered species.
Penguins and Climate Change: A Case of "Winners" and
"Losers"
Even within a single ecosystem, there can be winners and
losers from climate change. The Adélie and Chinstrap
penguins in Antarctica provide a good example. The two
species depend on different habitats for survival: Adélies
inhabit the winter ice pack, whereas Chinstraps remain close
to open water. During the past 50 years, a 7–9°F increase in
midwinter temperatures on the western Antarctic Peninsula
has led to a loss of sea ice. Over the past 25 years, the
population of Adélie penguins decreased by 22%, while the
population of Chinstrap penguin increased by an estimated
400%.] |
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Additional Climate Change Information |
Climate Change and Carbon Dioxide
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change
and carbon dioxide.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Carbon Dioxide and Climate Change
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of carbon dioxide
and climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Environmental Group Warns Earth's Health at Risk
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A report by the World Wildlife Fund looked at thousands of animal populations
and found they have dropped significantly in 40 years. |
Sea Levels Rising at Fastest Rate in 3,000 years
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A group of scientists say sea levels are rising at record rates. Another group
found that January temperatures in the Arctic reached a record high. |
Capturing CO2 Gas Is Not Easy
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Most scientists agree that carbon-dioxide gas is partly to blame for climate
change: rising global temperatures. But capturing the CO2 gas released by power
stations is costly and difficult. |
Growth, Climate Change Threaten African Plants and
Animals
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Researchers believe Africa may lose as much as 30 percent of its animal and
plant species by the end of this century. |
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