Pushing the Boundaries of Life: Tropics
For many years, it was thought that tropical rainforests
were essentially unaffected by climate change Now studies are showing
that not only were they changed during past events like ice ages, but
some areas are being affected right now by warming. At Monteverde Cloud
Forest Reserve, Costa Rica, clouds are forming higher, drying out some
of the habitat and causing changes in flora and fauna.
The most celebrated peer reviewed case is the disappearance
of the golden toads, Bufo periglenes. Each year Dr. Alan Pounds and others
search for the distinctive orange amphibian in its restricted habitat
along a narrow, fog-bound ridge. About 1500 toads were sighted in 1987.
But now the breeding pools remain empty -- the toad has not been seen
since 1991 and is feared extinct.
The golden toad and more than 60 other amphibians and lizards studied by Dr. Pounds are in decline apparently due to regional temperature increases lifting the level of clouds, changing the moisture regime and affecting a fungus that can be fatal to the animals. The species shown here, Atelopus varius, once common throughout Costa Rica, was not found at all in a recent survey, according to Dr. Pounds. The loss
of the golden toad and other amphibians in Monteverde, Costa Rica, is particularly troubling because
their habitats in the preserve are protected in the largely pristine montane rainforest. One cannot blame
habitat loss—a major cause of amphibian declines worldwide. A recent global survey of frogs and toads
showed that nearly all species listed as “possibly extinct” live in seemingly undisturbed habitats. Oregon State University herpetologist
Andrew Blaustein notes that half of the amphibians that have been the object of recent studies
have been breeding earlier, a trend that correlates with evidence of global warming. Yet climate change,
he points out, is but one factor in species disappearing; disease, pesticides, and wetland destruction must
also be factored in.
As for the loss of amphibians in Central America, Pounds suspected another culprit: an introduced
chythrid fungus, known to attack the skin of amphibians, that had somehow reached epidemic
proportions. In a paper published in January 2006, Pounds and colleagues hypothesized an
unpredictable synergy that climate can have with disease. Careful cross-analysis of temperature,
moisture, and optimum growing conditions for the chythrid fungus indicated that a warming climate
favored the pest, allowing it to infect the skin of many frogs and kill them. This was especially true at
elevations from 3,300 to 7,900 feet (1000–2400 m), where night temperatures rose and, during the day,
warmer moist air increased cloudiness, protecting the fungus from hot sunlight. For more information on current amphibian research, see here.
Dryer conditions in the cloud forest concern Dr. Karen
Masters, who studies tiny Pleurothallic canopy orchids. Lenghtening dry
periods could drive some into extinction. "We are now seeing 2, 3
even 5 days in a row without moisture." she reports. "This is
very challenging to these orchids." Also, recent repeat surveys of
bats by Dr. Richard LaVal, and of birds by Debra DeRosier (repeating a
1979 survey by Dr. George Powell) shows lowland, dry habitat species are
already moving higher into former cloud forest areas.
Other big changes are being monitored in the tropics, too. Sixteen years of data on tree growth, tropical air temperatures and CO2 readings indicate that a warming climate may cause the tropical forests to give off more carbon dioxide than they take up. This wouldupset the common belief that tropical forests are always a sink for carbon, taking huge amounts out of the atmosphere.
The study, by Deborah and David Clark of the La Selva biological station in Costa Rica, and Charles Keeling and Stephen Piper of the Scripps Institution, reports that rainforest trees grow much more slowly in warmer nighttime
In other parts of the tropics, even in places that have been undisturbed for more than 4500 years, the rise in atmospheric CO2 appears to be changing the composition of the forest. In a paper in the 11 March 2004 issue of Nature, William Laurance and colleagues document that many tree genera in Amazonia are growing faster than they were in the 1980s.
Other tree types are declining in vitality. The study of 13,700 trees in 18 very isolated plots in Brazil concluded that increased carbon dioxide is the most plausible explanation for the abrupt shifts in species growth. This "could also have serious ecological repercussions for the diverse Amazonian biota" wrote the scientists.
Update: 2010 Brings Another Severe Bleaching to the World's Coral.
Ocean temperatures in the western Pacific and the Caribbean are extraordinarily high throughout most of 2010, another reminder that global warming's effects are continuing. In the Caribbean, they are even worse than those of 2005 which bleached and damaged so much of the coral there, including endangered coral species in Virgin Islands National Park. See details about bleaching and the areas affected previously, below.
Information, alerts and maps for current conditions are available from NOAA at http://coralreefwatch.noaa.gov/satellite/baa/index.html and from the Smithsonian, at http://www.eurekalert.org/pub_releases/2010-10/stri-srr101210.php and Science journal, at http://news.sciencemag.org/sciencenow/2010/10/caribbean-coral-die-off-could-be.html
Coral reefs are probably the most complex ecosystems on the planet, home to hundreds of thousands of species. Reefs offer coastal protection to eighty-six nations, as well as income estimated at $375 billion through fishing, recreational opportunities, and new drugs. The damage being caused to reefs and the open ocean is one of the most serious effects of global warming.
These images are of the Great Barrier Reef, the largest reef on the planet and probably the most complex ecosystem, home to hundreds of thousands of species ranging from sharks to bacteria. Reefs are made of the calcium carbonate skeletons of the colonial coral polyp and as such represent a cycling, balance and storage of carbon. Climate change now threatens the ocean and corals in particular in two ways. First, oceans have warmed as much as a degree above the normal only a half century ago.
Second, oceans are getting more acidic because they naturally absorb CO2, including about a third of human-made emissions. This is creating a rapid, dangerous change in water chemistry that can slow or reverse shell and coral growth. Slower growth is already seen on some reefs, and tiny plankton – base of the food chain and source of half of Earth’s oxygen – will also be damaged as CO2 increases. For more information from a scientific paper about the threat to coral reefs, please see.
Rising sea temperature coupled with the strong El Nino of 1998 was devastating to much of the world's coral reefs. High water temperatures caused coral bleaching and subsequent death or adverse change to sixteen percent of world reefs overall and up to 46 percent in parts of the Indian Ocean.
Temperatures beyond norms causes coral to expel the microscopic symbionts, zooxanthellae, that also give them color. If this bleaching continues for days to weeks, the coral dies and algae takes over the reefs, changing the ecosystem. During another bout of bleaching in 2002, the international coral reef information network ReefBase reported 430 cases of coral bleaching, most of them on the Great Barrier Reef, the world's largest. Bleaching was also very extensive in the U.S. Virgin Islands National Park during 2005.
As it takes up heat, ocean water expands -- the major cause of sea level rising at a rate now exceeding 8 inches a century. Sea level rose about 6 inches in the 20th century, but the rise is predicted to increase to as much as a meter by 2100 (see Coastlines and Glacier sections). Coral, which thrives at and near the sea surface, is not expected to be able to keep pace with this rapid increase in water depth. In addition, seas are dissolving more and more carbon dioxide. Even though this adds more carbon, a raw material for coral making calcium carbonate reefs, it also acidifies the water, actually inhibiting the growth of coral.
Coupled with damage from human activities and development,
this growing danger has lead some scientists to predict the end of reefs
across much of the ocean. In reports in 1999 and 2004, Australian
Marine Biologist Ove Hoegh-Guldberg and others said high water temperatures
and bleaching will become yearly events before mid-century. Living
coral may be reduced by 95 percent on the Great Barrier Reef. Hough-Guldberg
said recently, "We are damaging a large part of the world's biodiversity"
on the reefs. "We're 'chopping them down' with global warming.
These reefs will be so changed that we'll have to find ways to re-employ
all those people," the millions who depend directly on reef fisheries
and recreation. "The implications are huge."
For a current report on a Pacific Island nation that is threatened by higher sea levels, and other places that are being inundated, see Coastlines.
For a look at climate-driven events in the North Atlantic, see the Arctic section.
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