The Changing Arctic Food Chain
Climate change is
affecting caribou (wild
reindeer).
Image courtesy of Dean
Briggins, U.S. Fish and
Wildlife Service.In the Arctic, shrubs are slowly infiltrating territory where once there was only ice, snow, and
lichens. Although these unassuming, stunted plants may not seem like much of a threat, their
expansion—driven by warming temperatures across the Arctic—is causing a cascade of ecological
impacts through the region's food chain.
Caribou—or wild reindeer—are a key species in the arctic
ecosystem. They are a critical food source for bears,
wolves, and a range of carrion feeders, as well as for
indigenous peoples across the region. A warmer climate
may help caribou in some ways: Warmer arctic summers
tend to increase food availability and, as a consequence,
survival of caribou calves. But these advantages
are countered by other effects of climate change. Shrubs
are crowding out lichens, a key winter food for caribou,
and the deep snowdrifts that collect in the shrubs make
it harder for caribou to reach the lichens hidden underneath.
Additionally, cycles of thawing and refreezing are
happening more and more throughout the winter, producing
a buildup of ice on top of the snow that makes it difficult
for caribou to access the food beneath.
The increasing number of shrubs is also speeding up the region's rate of warming. Snow
trapped by shrubs creates a thick blanket that insulates the soil, keeping it relatively warm over
much of the winter. In response, arctic microbes increase their processing of organic matter
in the soil, making the soil even more suitable for shrubs to grow, thus further increasing the
shrubs' capacity to warm the soil.
Ice-Dependent Animals
This map shows
the average arctic
sea ice
area for
September 2007
(in white) and
the
average from
1979 to 2000
(pink outline).
Image courtesy of the
National Snow and
Ice
Data Center.Sea ice is a critical resource for some of the world's
most beloved animals. Walruses, for example, use sea
ice as nursing platforms for their young and as a hunting
base from which they feed on clams and other bottom-dwellers. Each spring, walruses follow their sea ice
perches northward as the ice melts off in the south.
Because of climate change, the range of year-round
sea ice is shrinking, leading walruses to move farther
north each year. In 2007, the ice moved beyond the
edge of the continental shelf, where the water becomes
too deep for the walruses to feed. For the first time in recorded or oral history, thousands of walruses—seeking an alternate place to
rest between feeding excursions—set up camp along the beaches near the village
of Wainwright, Alaska. This dense aggregation of animals crushed many calves as
adults moved to and from the ocean to feed; over time, such a densely packed population
could also deplete bottom food resources along the coast.
Polar bears also rely on sea ice for hunting. When the sea is covered with ice,
bears can wait at openings in the ice for their favorite prey—ringed seals—to surface
for air. Where sea ice has melted, leaving only open sea, seals can surface
anywhere making it difficult for the polar bears to catch them.
A Fast Defrosting Arctic
The Arctic is
warming about
twice as fast as
the rest of the
planet as shown
by the large
area
of dark red.
Image created with
data from
the Goddard
Institute for Space
Studies.The Arctic is heating up about twice as rapidly as the rest of the planet. This is due in part
to several "feedback loops" in which the consequences of arctic thawing drive temperatures
even higher. For example, as sea ice and seasonal snow cover melt, previously reflective white
surfaces are converted to darker ocean water or vegetation, respectively. These dark surfaces
absorb more solar radiation, leading to higher
air temperatures which leads to even more
rapid melting, and so on.
Thawing permafrost represents another potential
feedback loop. Permafrost, the permanently
frozen ground found throughout cold regions,
contains a great deal of carbon in the form of
partially decomposed organic matter. As permafrost
warms, the microbes that decompose this
material become more active, releasing carbon
dioxide and methane into the atmosphere.
This web page is based on the National Academies' educational booklet
Ecological Impacts of Climate Change.
