Oceans Losing Ability to Absorb Carbon Dioxide

Oceans Losing Ability to Absorb Carbon Dioxide



 
 May 2007 -   Recent climate change brought on by 
human activities has weakened one the Earth's natural defenses against 
global warming. Atmospheric carbon dioxide is not being absorbed by the 
Southern Ocean as quickly as it once was, an international research team 
has found. 
Scientists have observed the first evidence that the Southern Ocean’s 
ability to absorb the major greenhouse gas carbon dioxide, CO2, has 
weakened by about 15 percent per decade since 1981. The study was 
published today in the journal "Science." 
"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," said lead author Dr. Corinne Le Quere of the University of 
East Anglia and the British Antarctic Survey. 
Dr. Corinne Le Quere is on the faculty of the School of Environmental 
Sciences, University of East Anglia and is a strategic alliance senior 
fellow at the British Antarctic Survey. 
"All climate models predict that this kind of feedback will continue and 
intensify during this century," said Dr. Le Quere. 
"The Earth’s carbon sinks – of which the Southern Ocean accounts for 15 
percent – absorb about half of all human carbon emissions. With the 
Southern Ocean reaching its saturation point more CO2 will stay in our 
atmosphere," she said. 
Such weakening of one of the Earth’s major carbon dioxide sinks will lead 
to higher levels of atmospheric carbon dioxide in the long term. 
And the study suggests that stabilization of atmospheric carbon dioxide 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 scientists 
said. 
Research vessel makes its way across the Southern Ocean. 
The international team included researchers from CSIRO in Australia, the 
Max-Planck Institute in Germany, the University of East Anglia and British 
Antarctic Survey in England, the Climate Monitoring and Diagnostics 
Laboratory in the United States, New Zealand's National Institute of Water 
and Atmospheric Research, the South African Weather Service, LSCE/IPSL and 
CNRS in France, and the Centre for Atmospheric and Oceanic Studies in 
Japan. 
Professor Chris Rapley, director of British Antarctic Survey said, "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." 
The saturation of the Southern Ocean was revealed by scrutinizing 
observations of atmospheric carbon dioxide from 40 stations around the 
world. 
The data show that since 1981 the Southern Ocean sink ceased to increase, 
whereas CO2 emissions increased by 40 percent. 
Dr. Paul Fraser, who leads research into atmospheric greenhouse gases at 
CSIRO Marine and Atmospheric Research, says the team’s four year study 
concludes that the weakening is due to human activities. 
"The researchers found that the Southern Ocean is becoming less efficient 
at absorbing carbon dioxide due to an increase in wind strength over the 
ocean, resulting from human-induced climate change," Dr. Fraser says. 
Data from the monitoring station at Cape Grim, Tasmania, Australia was 
used in the Southern Ocean carbon sink study. 
"The increase in wind strength is due to a combination of higher levels of 
greenhouse gases in the atmosphere and long-term ozone depletion in the 
stratosphere, which previous CSIRO research has shown intensifies storms 
over the Southern Ocean," he said. 
The increased winds influence the processes of mixing and upwelling in the 
ocean, which in turn cause an increased release of carbon dioxide into the 
atmosphere, reducing the net absorption of carbon dioxide into the ocean, 
he explained. 
Dr. Fraser points to one piece of good news - ozone levels in the 
stratosphere have stopped declining and should recover slowly in coming 
decades. 
"Thus the impact of ozone depletion on the Southern Ocean carbon dioxide 
sink will lessen in the future," he said, "but the impact of increasing 
levels of greenhouse gases will continue unabated."    
       
      

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