Geoscience Reference
In-Depth Information
likely sea level rise will be 1.5 to 1.8 meters
(5 to 6 feet) in the next hundred years. His
number comes from an analysis of perma-
frost and sea ice changes, accelerating ice
sheet melting, and increased thermal ex-
pansion. A rise of two meters (seven feet) is
not out of the question, and prudent plan-
ners should assume the higher figure.
The process by which ocean waters are
becoming more acidic is called ocean acidi-
fication, a term first used in the scientific
literature in 2003. The average ocean wa-
ter pH, or acidity, is now 8.1, compared to a
pre-industrial pH of 8.2. On the steep loga-
rithmic pH scale, that apparently small dif-
ference represents a 30% increase in acidity.
Jelle Bijma of the Alfred Wegner Institute
says that under a business-as-usual (bau)
scenario the surface waters of the oceans
are likely to become 150% more acidic by
2100.
The delicate chemical balance which
allows calcium carbonate (CaCO
3
)
to be
extracted from seawater and used by all
kinds of marine organisms to form shells
and skeletons has been disrupted. A por-
tion of the CO
2
that dissolves in seawater
forms carbonic acid (H
2
CO
3
), which in large
part controls the pH of the water. Carbonic
acid is forming at a higher rate now because
more CO
2
is being dissolved in seawater.
Seas around the Arctic and the Antarctic
are expected to experience acidification at a
faster rate than other oceans, because cold
water can take up more CO
2.
CaCO
3
is alkaline, or basic, the opposite
of acidic. Because acidification makes the
extraction of calcium carbonate from sea-
water by marine organisms more difficult,
these animals will have a harder time mak-
ing their shells, which will become thinner
and more fragile. Certain critically impor-
tant bacteria (such as the marine
Rose-
bacter clade
) that break down chemical com-
pounds in the water as part of the ocean's
ocean acidification:
one of the evil Twins
Roger Revelle and Hans Suess, two geochem-
ists at the Scripps Institution of Oceanogra-
phy, envisioned the possibility back in 1956
that the ocean would turn more acidic be-
cause of excess CO
2
. But this remained an
academic curiosity until the last decade.
Since then their suggestion has become re-
ality in rapid fashion. In just the last five
or six years this “new” greenhouse-related
ocean phenomenon has come to the fore in
the eyes of mainstream science. According
to a seminal report by the Royal Society
of London (2005), it has the potential for
a more important impact on marine life
than both global warming and overfish-
ing. Recently the state of the science on
ocean acidification was summarized in a
series of papers in the December 2009 is-
sue of
Oceanography
, and in 2010 the Euro-
pean Science Foundation presented a com-
prehensive policy briefing on the subject.
Ocean acidification is sometimes called one
of the evil twins of global ocean change, the
other twin being sea level rise.
