Climate change weakens Southern Ocean carbon sink

NIWA Media Release 17 May 2007
Embargoed to 0600 NZT on Friday May 18 2007

Climate change weakens Southern Ocean carbon sink

The first evidence that recent climate change has weakened one the Earth’s natural carbon ‘sinks’ is published this week in the journal Science.

The results of the four-year international study reveals that an increase in winds over the Southern Ocean, caused by greenhouse gases and ozone depletion, has led to a release of stored carbon dioxide (CO2) into the atmosphere and is preventing further absorption of the greenhouse gas. The study involved researchers from the UK, Germany, Australia, France, Japan, New Zealand, South Africa, and the US.

Lead author Dr Corinne Le Quéré of the University of East Anglia and British Antarctic Survey said,

“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. This is serious. All climate models predict that this kind of ‘feedback’ will continue and intensify during this century. The Earth’s carbon sinks – of which the Southern Ocean accounts for 15% – absorb about half of all human carbon emissions. With the Southern Ocean reaching its saturation point more CO2 will stay in our atmosphere.”

This new research suggests that stabilisation of atmospheric CO2 is even more difficult to achieve than previously thought. Additionally, acidification in the Southern Ocean is likely to reach dangerous levels earlier than the projected date of 2050.

The saturation of the Southern Ocean was revealed by scrutinising observations of atmospheric CO2 from 40 stations around the world, and combining this information with oceanic observations and high precision modelling.

One of the study’s authors, Antony Gomez of the National Institute of Water & Atmospheric Research (NIWA), helped extract and analyse Southern Hemisphere CO2 measurements. NIWA’s atmospheric monitoring station at Baring Head, near Wellington, provides the longest-running continuous measurement of Southern Hemisphere CO2.

Mr Gomez said,

“The Baring Head measurements show that CO2 concentrations were rising steadily through most of the 1980s and 90s at a rate of about 1.5 ppm [parts per million] per year. But the growth rate has accelerated since then and is now at about 2 ppm per year. The study shows that this trend is caused not only by higher emissions but also by the weakening carbon sink. CO2 emissions increased by 50% since 1981 but the Southern Ocean CO2 sink remained the same.”

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 Southern Ocean is the strongest ocean sink.

ENDS

The paper, ‘Saturations of the Southern Ocean CO2 sink due to recent climate change’ is published this week in Science. Authors: Corinne Le Quéré, Christian Rödenbeck, Erik T Buitenhuis, Thomas J Conway, Ray Langensfelds, Antony Gomez, Casper Labuschangne, Michel Ramonet, Takakiyo Nakazawa, Nicolas Metzl, Nathan P Gillett and Martin Heimann.

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