http://news.bbc.co.uk/2/hi/science/nature/3136266.stm
Last Updated: Wednesday,
24 September, 2003, 22:24 GMT 23:24 UK
BBC
Oceans becoming more acidic
By Richard Black
BBC science correspondent
QUOTE:
"We're understanding that ocean uptake of CO2 may at best
be a mixed blessing."
Ken Caldeira
The world's oceans
are slowly getting more acidic, say scientists.
The researchers from
California say the change is taking place
in response to higher levels of carbon dioxide in the atmosphere.
The lowering of the
waters' pH value is not great at the moment
but could pose a serious threat to current marine life if it continues,
they warn.
Ken Caldeira and Michael
Wickett, from the Lawrence Livermore National
Laboratory, report their concerns in the journal Nature.
Future
prospects
Increasing use of fossil
fuels means more carbon dioxide is going
into the air, and most of it will eventually be absorbed by seawater.
Once in the water, it reacts to form carbonic acid.
Scientists believe
that the oceans have already become slightly
more acidic over the last century.
But these researchers
have tried to predict what will happen
in the future by combining what we know about the history of
the oceans with computer models of climate change.
"This level of
acidity will get much more extreme in the future
if we continue releasing CO2 into the atmosphere," said Dr
Caldeira.
"And we predicted
amounts of future acidity that exceed anything
we saw over the last several hundred million years, apart from
perhaps
after rare catastrophic events such as asteroid impacts."
If carbon dioxide release
continues unabated, ocean pH could be
reduced by as much as 0.77 units, the authors warn.
Good and bad
It is not absolutely
clear what that means for marine life, however.
Most organisms live
near the surface, where the greatest pH change
would be expected to occur, but deep-ocean lifeforms may be more
sensitive to pH changes.
Coral reefs and other
organisms whose skeletons or shells contain
calcium carbonate may be particularly affected, the team speculate.
They could find it much more difficult to build these structures
in water with a lower pH.
In recent years some
people have suggested deliberately storing
carbon dioxide from power stations in the deep ocean as a way
of
curbing global warming.
But Dr Caldeira said
that such a strategy should now be re-considered.
"Previously, most
experts had looked at ocean absorption of carbon
dioxide as a good thing - because in releasing CO2 into the atmosphere
we warm the planet; and when CO2 is absorbed by the ocean, it
reduces
the amount of greenhouse warming.
"Now, we're understanding
that ocean uptake of CO2 may at best
be a mixed blessing."
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