http://www.hindu.com/thehindu/holnus/008200705190322.htm
Sci. & Tech.
CO2 sponge losing ability to soak up extra emissions
London, (GUARDIAN NEWS SERVICE)
By James Randerson
Climate change 'feedback effect' in Southern Ocean - Stronger winds
reduce efficiency of carbon sink
One of the most important of the natural sponges which soak up carbon
dioxide in the atmosphere is working 30% less efficiently than a
quarter of a century ago, researchers say.
The Southern Ocean is responsible for soaking up the annual CO2
contribution of the UK and the Netherlands combined, but the study
shows that the ocean is absorbing the same quantity of the gas as it
was 24 years ago. Scientists had expected the amount of CO2 absorbed
would increase in line with rising levels in the atmosphere. The
change is due to increased winds over the ocean linked to climate
change and the depleted ozone layer.
"This is serious. All climate models predict that this kind of
'feedback' will continue and intensify during this century," said
Corinne Le Quere, part of the team at the University of East Anglia,
Norwich, which carried out the study. This is the first time that
we've been able to say that climate change itself is responsible for
the saturation of the Southern Ocean sink."
So-called carbon sinks such as the oceans, vegetation and soils soak
up around half of the extra CO2 we are pumping into the atmosphere
each year - some 9.3bn tonnes. The Southern Ocean alone is
responsible for parcelling up 0.7bn tonnes a year and storing it in the deep.
"Since the 1980s the Southern Ocean sink for carbon has not changed
at all, although CO2 emissions over the same period have increased by
40%," said Dr Le Quere. "We would expect that as the emissions and
the CO2 in the atmosphere have increased, the Southern Ocean sink
should also increase."
The team looked at measurements of CO2 in the atmosphere from 40
stations around the globe - 11 around the Southern Ocean itself. They
calculate that the efficiency of the Southern Ocean as a carbon sink
has dropped by 30% compared with the amount it would be putting away
if it had kept pace with levels of CO2.
The team used CO2 measurements in water collected during research
cruises in the Southern Ocean in 1998, 2000, 2001 and 2002 to check
their calculations. The scientists, who report their research in the
journal Science today, believe the reason for the change is an
increase in average wind speed across the ocean.
"The winds act to mix the oceans. So when you have strong winds you
have more water circulation and more mixing," said Dr Le Quere. More
mixing brings colder water up from the depths which is saturated with
CO2, so that it cannot accept any more from the atmosphere.
The increase in wind speed is partly a consequence of climate change
itself - one of a handful of "positive feedback" effects which look
likely to accelerate global warming. Because the world is warming
unevenly, pressure differences between different regions are
increasing. One consequence of this is increasing wind speed in the
Southern Ocean. The depletion of the ozone layer has also contributed
to higher winds.
"Since the beginning of the industrial revolution the world's oceans
have absorbed about a quarter of the 500 gigatons of carbon emitted
into the atmosphere by humans. The possibility that in a warmer world
the Southern Ocean - the strongest ocean sink - is weakening is a
cause for concern," said Chris Rapley, director of the British
Antarctic Survey.
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