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New study suggests oceans are losing the ability to absorb carbon dioxide

  • 11 Jul 2011, 17:34
  • Verity

New research published online this week suggests that man-made climate change is diminishing the ocean's ability to 'take up' CO2 from the atmosphere.

Plants, trees and the soil all absorb carbon from the atmosphere, but the ocean is the world's largest 'carbon sink' and since the industrial revolution, the ocean has probably soaked up between a third and half of all man-made CO2 emissions.

The removal of manmade CO2 from the atmosphere by seawater is clearly an important process. However, researchers now suggest that the ocean's ability to absorb atmospheric CO2 might be declining. It's a combination of atmospheric CO2 levels and seawater chemistry that determines how much CO2 seawater can hold, and warmer water cannot hold as much dissolved CO2 as cold water.

Researchers analysed existing CO2 and temperature data for the North Atlantic Ocean over the last three decades. Their results showed that for a large section of the North Atlantic, less CO2 has been able to dissolve as the surface temperature of seawater has risen. This is in line with previous research conducted in other oceans, such as the Southern Ocean and Sea of Japan, which have also been found to be taking up less CO2 as a result of man-made climate change.

When considering the same question, previous studies in the North Atlantic have come to conflicting conclusions. The authors of this new study suggest that this is down to a high degree of natural variability which can mask longer-term trends.

Professor McKinley, the study's author, says:

"Because the ocean is so variable, we need at least 25 years' worth of data to really see the effect of carbon accumulation in the atmosphere. This is a big issue in many branches of climate science - what is natural variability, and what is climate change?"

This new study considers nearly thirty years worth of data, which the team think is enough to determine a real trend. Their findings have big implications for how much CO2 will be absorbed by oceans in the future, given the projected temperature rise associated with man-made greenhouse gas emissions. McKinley says:

"...This is some of the first evidence for climate damping the ocean's ability to take up carbon from the atmosphere."

McKinley stresses the need for this type of analysis in other oceans so that ocean CO2 uptake trends can continue to be refined. But the results of the study demonstrate that on a warming planet, natural carbon sinks can't be taken for granted.

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