Oceans' Ability to Mop-Up Greenhouse Gas Declines
Oceans' Ability to Mop-Up Greenhouse Gas Declines

A new study has found that oceans are struggling to help regulate climate as more carbon dioxide, a leading greenhouse gas, is pumped into the atmosphere.  

The ocean absorbs more than one-quarter of all of the man-made carbon dioxide from cars, coal-fired plant emissions and clear-cutting of forests.
But a new study has found that with each passing year, the ocean is mopping up a smaller fraction of CO2 pumped into the atmosphere.

According to the study, the world's oceans last year took up a record 2.3 billion tons of carbon dioxide produced by burning fossil fuels.  But with the rapid growth in CO2 emissions, the authors say the amount of man-made CO2 absorbed by the ocean since 2000 may have declined by as much as 10 percent over previous years.

Samar Khatiwala is an oceanographer at Columbia University in New York and lead author of the study that found a growing imbalance between the amount of man-made carbon dioxide being pumped into the atmosphere and what the oceans, called carbon sinks, are able to handle.

"What these results are showing is that the ocean is a really sizeable sink, as we call it, of man-made CO2.  Unfortunately what our results are also suggesting is that the ocean may be becoming a less efficient sink of this carbon," he said.

The study looks at the amount of man-made carbon dioxide absorbed by the ocean each year from the beginning of the Industrial Age in 1765 until now.
Researchers developed a mathematical technique to look at the amount of CO2 mopped up by the ocean that included factors such as seawater temperatures and ocean salinity.

Khatiwala says that until the beginning of this decade, there was a balance between carbon emissions and the amount of CO2 it could absorb.  
But he said the ocean has become more acidic as a result of its carbon stores, making it less able to cleanse the atmosphere of increasing carbon dioxide emissions.

"If emissions started growing too rapidly, the ocean basically cannot keep up.  And in fact, that seems to have happened over the last 10 years," he explained.  "If you compare emissions in this decade versus the previous decade, it was something like three times higher between 2000 and 2005 compared to the previous decade.  So it's really not surprising that the ocean is having a hard time keeping up," he added.

Other climate models have predicted a slow-down in the percentage of carbon dioxide emissions soaked up by ocean, but Khatiwala and colleagues are the first to measure the amount of reduction.

Their fiding was published in an article this week in the journal Nature.