Dear EarthTalk: I’ve heard about the
die-off of coral reefs due to global warming. I’ve also
read that coral reefs release carbon dioxide (CO2), when they
die. Isn’t that a double whammy that increases the CO2
in the atmosphere?
— Tom Ozzello, Maplewood, MN
According to marine scientists, the world’s coral reefs—those
underwater repositories for biodiversity that play host to
some 25 percent of all marine life—are in big trouble
as a result of global warming. Data collected by the international
environmental group WWF (formerly World Wildlife Fund) show
that 20 percent of the world’s coral reefs have been
effectively destroyed and show no immediate sign of recovery,
while about 50 percent of remaining reefs are under imminent
or long-term threat of collapse.
Most scientists now agree that global warming is not a natural
phenomenon but a direct result of the continual release of
excessive amounts of CO2 and other “greenhouse” gases
into the atmosphere by human industrial and transportation
activity. And the small but prolonged rises in ocean temperature
that result cause coral colonies to expel the symbiotic food-producing
algae that sustain them. This process is called “bleaching,” because
it turns the reefs white as they die.
But researchers working with the Coral Reef Alliance have found
that while coral reefs do store CO2 as part of photosynthesis,
they tend to release most of it back into the ocean (so they
are not what are known as “carbon sinks”). As such,
the release of CO2 from dying coral reefs is not a major concern.
Of course, the ocean itself is a large carbon sink, storing
about a quarter of what would otherwise end up in the atmosphere.
Landmasses (and their plants) soak up another quarter of all
the CO2 emanating from the Earth’s surface, while the
rest rises up into the atmosphere where it can wreak havoc
with our climate.
Recent findings indicate that the Antarctic Ocean is getting
less efficient at storing CO2, and this raises serious questions
about the ability of our oceans to handle everything we throw
at them. The study’s authors fear that “such weakening
of one of the Earth’s major carbon dioxide sinks will
lead to higher levels of atmospheric carbon dioxide in the
Not everyone is forecasting gloom and doom. Some Australian
researchers believe that coral reefs around the world could
expand in size by up to a third due to increased ocean warming. “Our
finding stands in stark contrast to previous predictions that
coral reef growth will suffer large, potentially catastrophic,
decreases in the future,” said University of New South
Wales oceanographer Ben McNeil in the peer-reviewed scientific
journal, Geophysical Research Letters. “Our analysis
suggests that ocean warming will foster considerably faster
future rates of coral reef growth that will eventually exceed
pre-industrial rates by as much as 35 per cent by 2100,” he
In spite of such theories, the majority of marine scientists
remain pessimistic about the future of coral reefs in a warmer
world. One can only hope that the optimists are right.
For information visit www.coralreefalliance.org; “Coral
reefs may grow with global warming,” New Scientist, www.newscientist.com/article/dn6763.html.
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