Oceans' ability to absorb carbon on the decline

Researchers are meeting in Norway this week to discuss the latest scientific findings on the carbon cycle, including the discovery that oceans appear to be absorbing less carbon dioxide than before and are also growing more acidic.

The gathering in Os aims to review the results of a five-year study on ocean carbon sources and sinks, the EU’s biggest such undertaking to date.

Among the project’s findings:

• Carbon dioxide uptake in both the North Atlantic and the Southern Ocean appears to be reduced (up until now, the oceans have absorbed about one-third of all human-generated carbon dioxide emissions);
• The carbon cycle climate feedback is re-enforcing climate change; and
• Ccean acidification is happening.

Atmospheric carbon dioxide levels are currently about 385 parts per million, compared to pre-industrial levels of about 278 parts per million. Today’s concentrations would be even higher if nature didn’t act as a “carbon sink” to absorb some carbon dioxide. For example, the oceans today take up about 25 per cent of our annual carbon dioxide emissions.

The five-year, €14.5-million CARBOOCEAN-project, which is coordinated by the Bjerknes Centre for Climate Research, is dedicated to improving our understanding of how oceans absorb man-made carbon emissions. More than 70 scientists participating in the project are meet in Solstrand outside Bergen this week to assess the results.

One discovery they will discuss is that, in considerable areas of the North Atlantic and the Southern Ocean, the surface CO2 partial pressure has temporarily increased faster than that in the atmosphere, which indicates a decrease in the ocean carbon dioxide sink. This potential decrease in CO2 sink and the underlying mechanisms will need further study.

Future scenarios with coupled ocean-atmosphere-land models show that the carbon cycle climate feedback re-enforces climate change. As shown by Earth system models, atmospheric carbon dioxide concentrations by the end of the 21st century will be 6 to 40 per cent higher than previous estimates, meaning emission targets for carbon dioxide will need to be adjusted accordingly.

One consequence of the oceans absorbing carbon dioxide is that they are becoming more acidic. That has implications for a wide variety of marine life, in particular creatures with carbonate shells that are harder to produce in acidic conditions.