Scientists unveiled the first smoking-gun evidence Wednesday that
growing ocean acidity caused by global warming is already stifling
growth of vital coral reefs.
The decline of shallow water corals, home to a quarter of the ocean's
species and a lifeline for a billion people, has long been in evidence.
Earlier studies had shown that the rate at which living coral reefs
calcify, or accumulate mass, had dropped by about 40 percent in just
over 30 years.
Up to now, however, it was not possible to tease out the impact of
acidification from other threats such as pollution, over-fishing and
warming water.
The world's oceans are 26 percent more acidic today than at the start
of the Industrial Revolution, when mankind started massively burning
fossil fuels which give off harmful carbon dioxide (CO2).
About a quarter is absorbed by the oceans, changing their chemical
composition, and making the water more acidic and corrosive to corals
and shellfish.
"Our work provides the first strong evidence from experiments on a
natural ecosystem that ocean acidification is already slowing coral reef
growth," said Rebecca Albright, a researcher at the Carnegie
Institution for Science in Stanford, California.
"This is no longer a fear for the future. It is the reality of today."
The findings were published in the science journal Nature.
Albright and colleague Ken Caldeira led experiments on natural reefs
off the coast of Australia's One Tree Island, in the southern Great
Barrier Reef.
Deep cuts
Manipulating the chemistry of the seawater flowing over the flat
reef, the researchers restored it's pH -- the balance between alkalinity
and acidity -- to what it would have been without climate change.
As suspected, the corals became better able to build themselves up.
"By turning back time in this way, they demonstrate that -- all
things being equal -- net coral-reef calcification would have been
around seven percent higher than at present," Janice Lough, a scientist
at the Australian Institute of Marine Science, noted in a comment, also
published in Nature.
The novelty of the experiment, she said, is that it "restored the
ocean chemistry of a natural reef to that of pre-industrial times, thus
factoring out other potentially confounding factors, such as
temperature."
Some researchers have proposed artificially reducing the acidity of
ocean water around coral reefs -- a form of geo-engineering -- as a
means of preserving shallow marine ecosystems.
But even if the experiments underlying the study did exactly that,
implementing such a scheme on the required scale would be nigh
impossible, the authors caution.
"The only real, lasting way to protect coral reefs is to make deep cuts in our carbon dioxide emissions," Caldeira said.
"If we don't take action on this issue very rapidly, coral reefs --
and everything that depends on them, including both wildlife and local
communities -- will not survive into the next century."
Coral reefs, like these in the lagoon of
the Toau atoll, about 400 km from Tahiti in the Tuamotu Archipelago on
October 18, 2015, are home to a quarter of the ocean's species and a
lifeline for a billion people (AFP Photo/Gregory Boissy) 