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Biological Effects of Global Warming
Small changes in temperature can have major effects on
ecological communities, changing the species mix,
disrupting food chain interactions, causing species
extinctions or migrations.
Here are a few examples:
In the arctic, plants have been moving steadily northward as the climate warms.
ice
polar desert
tundra
boreal forest
temperate forest
shrub expansion
tree expansion
no change
??
uncertain
?
The fatty, oily Arctic cod is ideal prey for seals,
narwhals and salmon in the Arctic, but global
warming could be shaking up the entire food web and
starving the cod itself because of shrinking and
shifting pack ice. Sea ice, marine plants, plankton
and Arctic cod form an inter-related food web that
sustains other animals such as polar bears and ivory
gulls. Now, however, the delicate process by which
the marine plants grow from the sea ice is
threatened by global warming.
"Global warming is pulling the rug out from beneath
the Arctic's food supply because the survival of
many plants and animals depends on the explosive
summer bloom of marine plants under the sea ice,"
says Chris Haney, chief scientist for Defenders of
Wildlife. "With more sea ice melting and retreating
from shore due to global warming, the plants' bloom
cycle is likely to be disrupted, jeopardizing the cod
and other species that depend on it. If this happens,
the cupboards in the pack-ice kitchen will become
increasingly bare to whales, seals and fish that
depend on the cod for food."
When the planet warms and formerly ideal
habitats become hot and dry, creatures must
move or die. The Edith's checkerspot butterfly
is no exception. This colorful butterfly once
inhabited the West Coast from northern
Mexico to southern Canada.
In the past 40 years, southern and low-lying checkerspot populations
have been dying off faster than those elsewhere. Plants on which
checkerspot caterpillars live and feed in these areas are withering
away due to increased temperature and droughts, thus starving the
insects before they can become butterflies. As a result, the
butterfly's range has shifted north by 63 miles, perhaps dooming the
southernmost subspecies, the endangered Quino, to eventual
extinction.
In the Lamar Valley in Yellowstone there are now
more gophers and grizzly bears, increases supported
by the spread of an invasive Mediterranean plant,
the Canada thistle. It appeared in North America
several centuries ago and has been in the park since
at least the 19th century.
It has expanded its range as wetlands have dried
during recent droughts. With warming
temperatures, the length of the growing season each
year has expanded by 20 days since the mid 1990s,
probably further favoring the thistle. It now covers
about twice as much area in the valley as it did in
1980.
Pocket gophers love the abundant, starchy roots of
the thistle and burrow beneath it to harvest the
roots and stockpile the part they don’t eat. While
churning the surface soil, the gophers create ideal
habitat for expansion of the plants, which then
support more gophers. This allows a rapid, positive
feedback expanding the population of both thistles
and gophers.
Grizzlies also love the thistle roots and
have learned to raid the gophers’
stockpiles. They also eat gophers and
their pups. More grizzles have moved
into the valley to take advantage of
these expanding food sources. The
major shift toward thistles and gophers
appears to have happened in 2004 when
another bear staple, white bark pine
nuts, was scarce.
Robert Crabtree of the Yellowstone
Ecological Research Center who has
been studying the thistle-gopher-bear
interaction says that as climate change
alters ecosystems “the winners are
going to be the adaptive foragers like
grizzlies that eat everything from ants
to moose, and the losers are going to
be the specialized species that can’t
adapt.”
For example the long tailed weasel
is declining. It feeds primarily on
voles, which are also declining.
Jim Robbins, AP
Some artic species may be able
to move rapidly in response to
changing climate.
Between Norway and the North
Pole lies Svalbard — an icy
Norwegian archipelago known
for glaciers, freezing winds and
polar bears. Swallowed by
glaciers until 10,000 years ago,
the island chain remains
dominated by ice that covers
60 percent of its surface.
Some artic species may be able to
move rapidly in response to changing
climate.
But in the part not covered by ice,
hardy Arctic plants like mountain avens
and white arctic bell heather have
staked out territory. And a new
analysis of thousands of samples of
nine species of these types of plants
reveals that Svalbard has been
colonized frequently and repeatedly
from all directions as it warmed and
froze over thousands of years,
indicating that Arctic plants can keep
up with climate changes.
Mountain avens, pictured here in Svalbard, is a
Russian immigrant originally, traveling
hundreds of miles to colonize the archipelago
as the climate warmed in the past.
The bell heather, pictured
here, can move fast and far
when required, having
traveled from Greenland to
Svalbard. The northward
creep of such species is a
leading indicator of Arctic
warming.
Svalbard has been repeatedly colonized by plants from
Greenland, Iceland and even Canada, though not often by
those from Scandinavia, its nearest neighbor to the south that
includes mainland Norway.
A report in Science suggested that recurrent glacial cycles
may have selected for a highly mobile arctic flora. In addition,
some dispersal vectors like wind may be particularly efficient
in the Arctic as a result of the open landscape.
Plant species living high in the Alps are climbing
farther up their summits to escape the heat of a
warming climate, but they risk going extinct when
they run out of mountain.
Surveying 26 summits, Austrian researchers
compared Alpine plant distribution with that
recorded nearly a century ago. They reported
species migrating skyward at a rate of about a
meter each decade in this century. At the same
time, the mean annual temperature increased less
than 1 degree Celsius.
In addition, not all plants moved at the same rate.
A small, yellow Alpine rose was the speediest,
moving about 4 meters a decade, while most other
herbs and grasses were moving less than 1 meter a
decade. Little is known of the biology of these
high-altitude species, and the basis for their
differences in migration speed remains elusive.
The purple mountain saxifrage is
vulnerable to overheating (swissinfo)
Similar patterns are being documented among animals in California's
mountains.
Jim Patton and his colleagues at the UC Berkeley Museum of
Vertebrate Zoology have been painstakingly counting animals in
Yosemite, Lassen and other wilderness areas in California, retracing the
steps of the museum's first director, Joseph Grinnell, who meticulously
catalogued the state's wildlife more than 80 years ago.
Grinnell's aim was to document what was living where in California in the
early part of the century so that future scientists would be able to
recognize the changes he was sure would occur. His foresight is paying
off as Patton et al. revisit the spots that Grinnell surveyed to see if
things have changed.
They have.
Several high-elevation species
appear to have retracted their
ranges upward.
The alpine chipmunk, found only
in California's high Sierra, was
spotted by Grinnell at an
elevation of 7,700 feet.
Patton's team hasn't found the
chipmunk lower than 9,700 feet.
"Since they can't go any higher
than the tops of these
mountains, if they keep
retracting upward, eventually
they're going to go extinct,"
Patton said. "Is that something
that's of concern to people? I
would hope so."
Alpine Chipmunk
Belding's ground squirrels have also withdrawn
their range upward by around 1,500 feet and the
golden mantle ground squirrel has lost several
hundred feet of elevation at the lower end of its
range as well.
Belding’s Ground Squirrel
Golden Mantled Ground Squirrel
Pika
The pika, a cousin of the rabbit, has moved the
lower limit of its range up 1,500 feet, a change
seen in pika populations in mountain ranges
throughout the west, resulting in local extinctions
of some populations.
"These are animals that are apparently very
sensitive to temperature increase, and a few
degrees of temperature increase in the summer can
cause death of individuals," Patton said.
At the same time, species typically found at lower
elevations are appearing at much higher elevations than
before. The pinyon mouse, which didn't exist in Yosemite
National Park in Grinnell's day, has expanded the upper
limit of its range from outside of the park at about 7,800
feet up into the park as high as 10,500 feet.
"I trapped the first one up on Mt. Lyell," Patton said.
"When I saw it, I thought, 'What in the world is this
animal doing up here? It's not even close to its habitat.'
That was a real surprise."
Pinyon Mouse
Now Patton and others at the MVZ are testing whether the
Yosemite patterns are reproduced statewide, in other places
such as Mount Lassen and the White Mountains that Grinnell
surveyed. And if the high-altitude range retractions are
pervasive, that will be another clue global warming is the likely
cause.
"I don't know what else would explain that," Patton said.
California Ground Squirrel
Global warming effects in the oceans
There are many disruptions of the ocean ecosystems overfishing, pollution, shipping-dependent introduction of
distant species. How can we tease out global warming effects?
The oceans are vast, so overall they warm slowly. Thus GW
effects can be studied most easily at their edges, in places of
local warming. We’ll look at two examples - the intertidal zone
and coral reefs.
In the ocean, intertidal zones provide a good laboratory for studying the
effects of global warming. They tend to undergo large daily temperature
fluctuations, especially when a low tide coincides with midday sun.
Global warming: lessons taught by snails and crabs
A long term study at the Hopkins Marine Station in Pacific Grove showed that
marine populations had changed dramatically in just 60 years, 1930-1993.
There was a significant decrease in northern species, those that tend to occur
to the north of Monterey Bay, but eight out of nine southern species increased
in abundance. Cold-loving species tended to move out, and warm-loving species
moved in.
Did a change in climate cause this shift in species distribution? Had the
temperature of Monterey Bay had changed since the 1930s.
Fortunately, Hopkins Marine Station personnel have been meticulously recording
seawater temperatures every day for nearly 80 years. The data showed that,
during the 60-year interval between the two animal surveys, annual mean water
temperatures increased on average by about 0.7 °C.
More significantly, peak summer temperatures in August rose nearly 2.2°C.
Although these temperature increases
seem relatively small, they may have
been substantial enough to push some
species over the edge of their thermal
tolerance range.
What effect will rising temperatures
have on marine organisms --- especially
on vulnerable intertidal creatures that
frequently are exposed to the hot rays
of the sun during low tide?
To find out, George Somero and
Jonathan Stillman at Hopkins
investigated thermal tolerance limits in
two groups of common Pacific
invertebrates -- porcelain crabs (genus
Petrolisthes) and snails (genus Tegula).
The question: are intertidal crabs and
snails are more susceptible to heat than
their subtidal cousins, which spend their
entire lives under water.
Along California’s central coast the
population of the intertidal porcelain
crab (Petrolisthes cinctipes) has
dramatically declined in the last 60
years as sea surface temperatures
have increased.
Lessons from crabs
Somero and Stillman collected 20 species of porcelain crabs from intertidal and
subtidal habitats in four Pacific regions: temperate coastal waters off California
and Chile, and subtropical and tropical areas off Mexico and Panama.
The thermal tolerance limit of each species was determined by raising the water
temperature in an experimental chamber by 1°C every 15 minutes, then
examining the number of survivors at each temperature interval.
The rate of 1 C per 15 minutes reflects the temperature increase that porcelain
crabs experience during extremely hot low tide periods.
The results show that porcelain crab species living at the surface are more
vulnerable to global warming than those that are always submerged.
For example, intertidal species from tropical waters off Mexico and Panama
succumbed when the thermometer reached 107 F (41 C) -- only about 1.8 F (1 C)
higher than the maximum temperature they currently experience in the wild.
Similar results were found among intertidal crabs from cooler waters off
California and Chile. These animals could tolerate temperatures between 32 to
35°C -- only slightly higher than their maximum habitat temperature of
31°C.
One intertidal crab species included in the study, Petrolisthes cinctipes, was a
common inhabitant of Monterey Bay 60 years ago, according to the ocean
survey conducted at Hopkins in the 1930s. But P. cinctipes showed a
significant decline in the 1993 re-survey, a finding that is consistent with the
thermal stress tests.
Overall, species from intertidal locations around the Pacific already are living at
the edge of their thermal limits and might not be able to survive even slight
temperature increases.
In contrast, subtidal species from all habitats turned out to have thermal
tolerance limits that, while lower than intertidal species, were much higher than
the maximum water temperatures they encounter in nature.
Lessons from snails
Another study compared the
thermal tolerance of two snail
species commonly found in Monterey
Bay. The first, Tegula funebralis,
lives near the surface and
frequently is exposed to full sun
during low tide. The other, T.
brunnea, is usually submerged and
therefore experiences less intense
heat during the day.
When kept at 30° C for 2.5 hours, T. funebralis continued to manufacture
proteins -- unlike its cousin, T. brunnea, which stopped nearly all protein
production and eventually died.
These data help to explain the different vertical distribution of these two
species of Tegula. The lower-occurring species, T. brunnea, simply cannot
continue to manufacture proteins at temperatures routinely experienced by its
higher-occurring cousin, T. funebralis.
But even T. funebralis is poised near its thermal tolerance limit. Therefore,
additional warming is likely to create serious problems for both snail species.
Another threat to ocean health - coral bleaching
The primary cause of coral bleaching is high water temperature. Temperature
increases of only 1.5–2°C lasting for six to eight weeks are enough to trigger
bleaching. When high temperatures persist for more than eight weeks, corals
begin to die.
Many other stressors can also cause bleaching including disease, sedimentation,
pollutants and changes in salinity. These stressors usually operate at local scales.
Elevated water temperature is of greater concern as it can affect reefs at
regional to global scales. When bleaching occurs at these large spatial scales, it
is a mass bleaching event.
Zooxanthellae (microscopic algae) live in the
tissue of many corals in a symbiotic relationship.
Up to 90 per cent of the coral’s energy
requirements comes from the zooxanthellae so
corals are highly dependant on this symbiotic
relationship.
Coral bleaching occurs when the coral host expels
its zooxanthellae. Photosynthetic pigments of the
zooxanthellae give corals much of their colour.
Therefore without the zooxanthellae, the tissue
of the coral animal appears transparent and the
coral’s bright white skeleton is revealed.
Coral polyp showing its tiny zooxanthellae,
seen as small brown dots. Source Kirsten
Michalek-Wagner
Corals begin to starve once they bleach. While some can feed themselves, most
corals struggle to survive without their zooxanthellae. If conditions return to
normal, corals can regain their zooxanthellae, return to normal color, and survive.
This stress, however, is likely to cause decreased coral growth and reproduction,
and increased susceptibility to disease.
Bleached corals often die if the stress persists. Coral reefs suffering severe
mortality following bleaching can take many years or decades to recover.
Where has coral bleaching occurred?
Mass bleaching has now affected every reef region
in the world. The spatial extent and severity of
impacts of coral bleaching have been increasing
throughout the world over the last few decades. A
particularly severe, worldwide bleaching event
occurred in 1998, effectively destroying 16 per cent
of the world’s reefs.
Bleached landscape of staghorn and
plate corals in 2006
A reef bleached white during the 1998
mass bleaching event
The Great Barrier Reef was affected by the 1998 global
bleaching event and by another event in 2002. More localised
bleaching occurred in the southern Great Barrier Reef in 2006.
Projected increases in global temperatures suggest that
bleaching will continue to increase over coming decades, placing
greater stress on reefs.
Another problem for corals — acidification of the oceans
Coral reefs face yet another threat induced by carbon dioxide pollution.
The increased carbon dioxide being absorbed by the ocean over the last
two centuries is making it more acidic.
Since the industrial revolution began, surface ocean pH has dropped by
slightly less than 0.1 units (on the logarithmic scale of pH), and it is
expected to drop by a further 0.3 - 0.5 units by 2100 as the ocean
absorbs more anthropogenic CO2.
As waters become more acidic, it becomes harder for coral and other
calcifying organisms like echinoderms and molluscs to form their CaCO3
skeletons. If the pH change goes far enough, the skeletons will begin to
dissolve.
A recent report concluded, “Since acidification is irreversible in our
lifetimes, the only practical step is to reduce emissions of carbon
dioxide as quickly as possible to minimize large-scale, long-term harm to
the world's oceans and marine ecosystems."
Projected risks due to critical climate change impacts on ecosystems
IPPC slide predicting the biological impacts of continued warming.