My latest Mind and Matter column in the Wall Street
Journal:
Coral reefs around the world are suffering badly from overfishing
and various forms of pollution. Yet many experts argue that the
greatest threat to them is the acidification of the oceans from the
dissolving of man-made carbon dioxide emissions.
The effect of acidification, according to J.E.N. Veron, an
Australian coral scientist, will be "nothing less than
catastrophic.... What were once thriving coral gardens that
supported the greatest biodiversity of the marine realm will become
red-black bacterial slime, and they will stay that way."
This is a common view. The Natural Resources Defense Council has
called ocean acidification "the scariest environmental problem
you've never heard of."
Sigourney Weaver, who narrated a film about the issue, said that
"the scientists are freaked out." The head of the National Oceanic
and Atmospheric Administration calls it global warming's "equally
evil twin."
But do the scientific data support such alarm? Last month
scientists at San Diego's Scripps Institution of Oceanography and
other authors published a study showing how much the pH level
(measuring alkalinity versus acidity) varies naturally between
parts of the ocean and at different times of the day, month and
year.
"On both a monthly and annual scale, even the most stable open
ocean sites see pH changes many times larger than the annual rate
of acidification," say the authors of the study, adding that
because good instruments to measure ocean pH have only recently
been deployed, "this variation has been under-appreciated." Over
coral reefs, the pH decline between dusk and dawn is almost half as
much as the decrease in average pH expected over the next 100
years. The noise is greater than the signal.
Another recent study, by scientists from the U.K., Hawaii and
Massachusetts, concluded that "marine and freshwater assemblages
have always experienced variable pH conditions," and that "in many
freshwater lakes, pH changes that are orders of magnitude greater
than those projected for the 22nd-century oceans can occur over
periods of hours."
This adds to other hints that the ocean-acidification problem may
have been exaggerated. For a start, the ocean is alkaline and in no
danger of becoming acid (despite headlines like that from Reuters
in 2009: "Climate Change Turning Seas Acid"). If the average pH of
the ocean drops to 7.8 from 8.1 by 2100 as predicted, it will still
be well above seven, the neutral point where alkalinity becomes
acidity.
The central concern is that lower pH will make it harder for
corals, clams and other "calcifier" creatures to make calcium
carbonate skeletons and shells. Yet this concern also may be
overstated. Off Papua New Guinea and the Italian island of Ischia,
where natural carbon-dioxide bubbles from volcanic vents make the
sea less alkaline, and off the Yucatan, where underwater springs
make seawater actually acidic, studies have shown that at least
some kinds of calcifiers still thrive-at least as far down as pH
7.8.
In a recent experiment in the Mediterranean, reported in Nature
Climate Change, corals and mollusks were transplanted to lower pH
sites, where they proved "able to calcify and grow at even faster
than normal rates when exposed to the high [carbon-dioxide] levels
projected for the next 300 years." In any case, freshwater mussels
thrive in Scottish rivers, where the pH is as low as five.
Laboratory experiments find that more marine creatures thrive than
suffer when carbon dioxide lowers the pH level to 7.8. This is
because the carbon dioxide dissolves mainly as bicarbonate, which
many calcifiers use as raw material for carbonate.
Human beings have indeed placed marine ecosystems under terrible
pressure, but the chief culprits are overfishing and pollution. By
comparison, a very slow reduction in the alkalinity of the oceans,
well within the range of natural variation, is a modest threat, and
it certainly does not merit apocalyptic headlines.
