Are the Oceans Really Stuffed to the Gills with Carbon Dioxide?

Two months ago, NASA’s Timothy Hall and colleagues published a study that described how they had estimated the amount of manmade carbon dioxide absorbed by the ocean since the start of the industrial era.

Oceans absorb about a third of the carbon dioxide that humans release into the atmosphere, so sorting out a long-term record of carbon uptake is of great interest to climate scientists.

To create their record of the ocean’s uptake of carbon, Hall and Samar Khatiwala, the lead author of the study, devised a clever mathematical technique that proved to be a considerable advance. When Hall’s study appeared in the journal Nature, he assumed the creation of this new long-term, continuous record would headline the news.

But journalists gravitated toward something else entirely: a brief mention that the amount of carbon dioxide absorbed by the ocean seemed to be experiencing, as the researchers put it, “a small decline in the rate of increase in the last few decades.”

“Seas Grow Less Effective at Absorbing Emissions”, one headline trumpeted. Another article compared the world’s oceans to a fish “stuffed to the gills” with carbon dioxide and another reported a “sudden and dramatic drop in the amount of carbon dioxide being absorbed by the sea.

Given the caveats included in the original study, all of this caught Hall slightly off guard. I’ll let Hall, who summarized his reactions to the coverage for What On Earth, pick the story up from here:

My coauthors and I had viewed the ability to estimate the history of ocean uptake of anthropogenic carbon as the highlight of the paper. Previously, observationally-based estimates had only provided a few snapshots in time, and we were proud of the cleverness of our techniques.

It seems clever mathematical techniques, however, don’t make good press releases. Interestingly, coverage of the paper has not focused on the fact that we can estimate the uptake history. Instead it has focused on apparent reductions in the rate of uptake over the last 2 decades.

The figure below shows our estimate of ocean uptake since 1775. The first impression is the rapid increase since 1950, coinciding with the rapid rise in carbon emissions to the atmosphere. The oceans have prevented about 1/3 of anthropogenic carbon emissions from accumulating in the atmosphere. A closer reading of the curve reveals a reduction in the uptake’s rate of increase after about 1980, even while emissions continue to increase.

Scientists have long suspected that ocean carbon uptake would eventually be unable to keep pace with rising emissions. Basic aqueous chemistry tells us that, as dissolved carbon in seawater increases, seawater becomes less able to absorb new carbon. Eventually, the absorption saturates. The slowing down of the increase rate may be an early signal of this saturation.

However, recent changes in uptake were not our focus when we performed the study, and more importantly we did not analyze the statistical significance of the slowdown. We plan further analysis on these trend variations. What we can say is that there are physical reasons to suspect a reduction in the ocean’s capacity to keep pace with increasing carbon emissions, and that there are now strong observational hints for recent reductions.

Hall advises reading this story, which also appeared in Nature. It’s less dramatic and more technical than most of media accounts, but it is a more accurate representation of the paper.

–Adam Voiland, NASA’s Earth Science News Team
   Image Credit: (EPOD/K. Chrisodoulopoulus)

6 thoughts on “Are the Oceans Really Stuffed to the Gills with Carbon Dioxide?”

  1. The conclusion that comes with these studies is that we can really change and that, as far as possible, the planet has absorbed the impact. It is as if we were in prehistoric times and was full of active volcanoes. What this causes heating, which causes dilation, which causes drift of continents, which causes an expansion of the global volume. Not to mention that global warming may cause melting of ice resting on the ground in Antarctica redistributing weight on the tectonic plates, increasing the volume of the oceans and increasing the rate of water evaporation, causing more storms and greater movement of the boiling air mass. Not to mention the pollution of habitats food suppliers. It seems a catastrophic scenario, and well, certainly to some extent is. The planet earth absorbs garbage that clogs up the sewer pit. And the problem of global warming is not just CO2 excess. Actually it is the very burning machine … where does the heat produced by the engines? Certainly rise … It is not just a greenhouse, there is a warming effect merely said, by fire. Solution? Several, but certainly no easy. With the existing movement for change in culture, the changes in the energy matrix, with the development of new technologies will solve the problem. Climate change will drive the man to new discoveries that finally retire the wood stove. I’m not afraid of the future, I believe more in the capacity of man.

  2. not sure how one can use a mathematical computation to work back to the early 18th century towards carbon deposits.

    like to see more factual data relating to actual measurements taken covering such date range rather than mathematical trickery which at best is nothing short of calculated probability factors… in short a guess?.

    peaple like to state figures base on mathematics that’s fare doo’s so how about working out the rate of temperature change caused from all the nuclear testing over the last 50 yrs.

    a fisherman who works around nelson island south pole recons the ice fields change from time to time and of late they have advanced more than they have over the last 15 yrs. so if global warming is a factor [please please explain this]

    4 sure we should make every effort to minimize human effects on a fragile planet, however when politicians use these as tools for taxation ,then we should start to look further than a closed empty box of facts.

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