Page 448 - Environment: The Science Behind the Stories

carbonate shells of marine creatures previous. These researchers concluded
like corals even begin dissolving 5 : that our oceans are well on the way to 280 ppm
losing coral reefs.
CaCO S Ca 1 CO 22
21
3 3 Paleontological studies of the fossil
Researchers have been testing how record lend support to this idea, show-
increasing acidity affects corals in the lab ing that coral reefs and other marine
and in the field. They’ve also been study- organisms using calcification experi-
ing the current global distribution of coral enced wide-scale population declines
reefs, the massive calcium carbonate and extinctions in the early Triassic
structures built by millions of tiny corals period during an episode of extremely Today: 380 ppm
that create habitat for so many other high atmospheric CO levels.
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marine animals. Through these research What should we expect in the
avenues they aim to make predictions future? A number of scientists have
about how coral reefs will fare in the looked to the Fourth Assessment
future as climate change proceeds. Report of the Intergovernmental Panel
In 2007, a team led by Ove Hoegh- on Climate Change (IPCC; p. 510), the
Guldberg of the University of Queensland 2007 consensus document summariz-
in Australia reviewed existing knowledge ing scientific knowledge on climate 500 ppm
of these questions and published its change to that point. Using the IPCC’s
conclusions in the journal Science. known and predicted data on atmos-
Chemistry tests in the lab show phere and ocean temperatures and
that coral shells begin to erode faster pH, these researchers modeled how
than they are built once the carbon- oceanic carbonate ion concentrations
ate ion concentration falls below 200 should change at various values for Reefs shrink Reefs grow
micromoles/kg of seawater. Researchers atmospheric CO .
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studying coral reefs in the field are finding The results predicted that as atmos- 0 1 2 3 4 5
the same thing: Reefs are growing only pheric CO levels rise, coral reefs will
2 Ω aragonite
in waters with greater than 200 micro- shrink in distribution, diversity, and den- Figure 2 increased atmospheric carbon
moles/kg of carbonate ion availability. A sity (Figure 2). By the time atmospheric dioxide levels have decreased the number
few calculations reveal that this concen- CO levels pass 500 ppm, little area of
2 of ocean areas that support coral reefs.
tration is what we would expect to result ocean will be left with conditions to sup- Most of Earth’s tropical and subtropical
from an atmospheric CO concentration port coral reefs. Most of the world’s coral oceans were suitable for the growth of
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of 480 parts per million (ppm). Earth’s reefs, home to so much vibrant biodiver- coral reefs (blue colors; top panel) before
natural (“preindustrial”) level was 280 sity, “will become rapidly eroding rubble people began emitting carbon dioxide to
ppm, and today we have raised it above banks,” Hoegh-Guldberg’s team wrote. the atmosphere. Today, at 380 ppm atmos-
380 ppm. Thus we are a little more than Without living and growing coral pheric CO (middle panel), fewer regions
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halfway to the point at which coral reefs reefs, the rich communities of reef- are suitable. When the planet reaches 500
will begin to dissolve in most of the areas dependent animals will likely collapse. ppm (bottom panel), very few areas of the
they now exist. At the rate CO is accu- For human society, fisheries will decline, ocean will have conditions suitable for coral
2 reefs. Adapted from Hoegh-Guldberg, O., et al.,
mulating in the atmosphere, we could tourism will wither, and coasts will lose 2007. Coral reefs under rapid climate change and CHAPTER 16 • M AR in E A nd Co A s TA l s ys TEM s A nd R E sou R CE s
easily reach 480 ppm around the middle protection against storm surges. Devel- ocean acidification. Science 318: 1737–1742. Fig 4.
of this century. oping nations and island nations in the Reprinted with permission from AAAS.
Hoegh-Guldberg’s team sought tropics—those already expected to suf-
some long-term context, so they used fer the most from climate change—will in the genus Acropora) will be able to
data from the Vostok ice core (p. 508), be hit hardest. colonize areas vacated by dying corals.
drilled from Antarctic ice, to look for Scientists are hoping there may What can we do about the threats
patterns from the past 420,000 years. be silver linings. Organisms vary in how from ocean acidification? Ultimately the
They found that in all that time, carbon- they react, and not all will suffer from the only effective solution is to reduce our
ate ion concentrations in the oceans ocean’s chemistry changes. Corals that carbon emissions, and soon. The clock is
had never been as low as they are are more tolerant to temperature changes ticking. In 2013, the Mauna Loa Obser-
today. Indeed, current sea tempera- (such as a variety called Porites) may suc- vatory in Hawaii measured 400 ppm of
tures are 0.7°C warmer and pH is 0.1 ceed where others fail. Perhaps certain atmospheric CO , the highest such read-
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unit lower than in the 420,000 years rapidly colonizing species (such as those ing for the last nearly 3 million years.
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