Oceans' uptake of manmade carbon may be slowing

Nov 18, 2009
Carbon released by fossil fuel burning (black) continues to accumulate in the air (red), oceans (blue), and land (green). The oceans take up roughly a quarter of manmade CO2, but evidence suggests they are now taking up a smaller proportion. Credit: Samar Khatiwala, Lamont-Doherty Earth Observatory

The oceans play a key role in regulating climate, absorbing more than a quarter of the carbon dioxide that humans put into the air. Now, the first year-by-year accounting of this mechanism during the industrial era suggests the oceans are struggling to keep up with rising emissions -- a finding with potentially wide implications for future climate. The study appears in this week's issue of the journal Nature.

The researchers estimate that the oceans last year took up a record 2.3 billion tons of CO2 produced from burning of . But with overall emissions growing rapidly, the proportion of fossil-fuel emissions absorbed by the oceans since 2000 may have declined by as much as 10%.

Some have already predicted such a slowdown in the oceans' ability to soak up excess carbon from the atmosphere, but this is the first time scientists have actually measured it. Models attribute the change to depletion of in the stratosphere and global warming-induced shifts in winds and ocean circulation. But the new study suggests the slowdown is due to natural chemical and physical limits on the oceans' ability to absorb carbon—an idea that is now the subject of widespread research by other scientists.

"The more you put in, the more acidic the ocean becomes, reducing its ability to hold CO2" said the study's lead author, Samar Khatiwala, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory. "Because of this chemical effect, over time, the ocean is expected to become a less efficient sink of manmade carbon. The surprise is that we may already be seeing evidence for this, perhaps compounded by the ocean's slow circulation in the face of accelerating emissions."

The study reconstructs the accumulation of industrial carbon in the oceans year by year, from 1765 to 2008. Khatiwala and his colleagues found that uptake rose sharply in the 1950s, as the oceans tried to keep pace with the growth of carbon dioxide emissions worldwide. Emissions continued to grow, and by 2000, reached such a pitch that the oceans have since absorbed a declining overall percentage, even though they absorb more each year in absolute tonnage. Today, the oceans hold about 150 billion tons of industrial carbon, the researchers estimate--a third more than in the mid-1990s.

For decades, scientists have tried to estimate the amount of manmade carbon absorbed by the ocean by teasing out the small amount of industrial carbon—less than 1 percent—from the enormous background levels of natural carbon. Because of the difficulties of this approach, only one attempt has been made to come up with a global estimate of how much industrial carbon the oceans held—for a single year, 1994.

Khatiwala and his colleagues came up with another method. Using some of the same data as their predecessors— seawater temperatures, salinity, manmade chlorofluorocarbons and other measures—they developed a mathematical technique to work backward from the measurements to infer the concentration of industrial carbon in surface waters, and its transport to deep water through ocean circulation. This allowed them to reconstruct the uptake and distribution of industrial carbon in the oceans over time.

Their estimate of industrial carbon in the oceans in 1994—114 billion tons—nearly matched the earlier 118 billion-ton estimate, made by Chris Sabine, a marine chemist at the National Oceanic and Atmospheric Organization in a 2004 paper in the journal Science.

Sabine, who was not involved in the new study, said he saw some limitations. For one, he said, the study assumes circulation has remained steady, along with the amount of organic matter in the oceans. "That being said, I still think this is the best estimate of the time variance of anthropogenic CO2 in the ocean available," said Sabine. "Our previous attempts to quantify anthropogenic CO2 using ocean data have only been able to provide single snapshots in time."

About 40 percent of the carbon entered the oceans through the frigid waters of the Southern Ocean, around Antarctica, because carbon dioxide dissolves more readily in cold, dense seawater than in warmer waters. From there, currents transport the carbon north. "We've suspected for some time that the Southern Ocean plays a critical role in soaking up fossil fuel CO2," said Khatiwala. "But our study is the first to quantify the importance of this region with actual data."

The researchers also estimated carbon uptake on land, by taking the known amount of fossil-fuel emissions and subtracting the oceans' uptake and the carbon left in the air. They were surprised to learn that the land may now be absorbing more than it is giving off.

They say that until the 1940s, the landscape produced excess carbon dioxide, possibly due to logging and the clearing and burning of forests for farming. Deforestation and other land-use changes continue at a rapid pace today—but now, each year the land appears to be absorbing 1.1 billion tons more carbon than it is giving off.

One possible reason for the reversal, say the researchers, is that now, some of the extra atmospheric carbon—raw material for photosynthesis--may be feeding back into living plants and making them grow faster. "The extra carbon dioxide in the atmosphere may be providing a fertilizing effect," said study coauthor Timothy Hall, a senior scientist at NASA's Goddard Institute for Space Studies. Many other scientists are now working to determine the possible effects of increased carbon dioxide on plant growth, and incorporate these into models of past and future climates.

Khatiwala says there are still large uncertainties, but in any case, natural mechanisms cannot be depended upon to mitigate increasing human-produced emissions. "What our study and other recent land studies suggest is that we cannot count on these sinks operating in the future as they have in the past, and keep on subsidizing our ever-growing appetite for fossil fuels," he said.

Source: The Earth Institute at Columbia University (news : web)

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defunctdiety
2 / 5 (8) Nov 18, 2009
Too bad this most recent bit of AGW PROPAGANDA is not academically honest, right along with AGW theory in general.

Good thing there's A LOT more that goes into it, as is shown by these two academically honest studies.

http://www.physor...715.html

http://www.physor...550.html
gmurphy
4.2 / 5 (5) Nov 18, 2009
Actually, if you had bothered to read the article properly, 2nd last paragraph, the absorption of CO2 by the land is fully acknowledged. Evidently, science which doesn't conform to your own beliefs isn't worth reading.
defunctdiety
2.3 / 5 (3) Nov 18, 2009
Admittedly I didn't read the last 4 paragraphs or so (at work, I skim) but it still doesn't change the fact that the AGW movement as a whole only presents 1 chapter out of a trilogy of novels, so to speak.

Thanks for pointing that out gmuprhy.

They do at least pay lip service to the tremendous uncertainty. This actually fits perfectly into the CO2 lag of rising temperatures trend too.
3432682
1.8 / 5 (5) Nov 18, 2009
CO2 absorption removes about half of what is released by burning fuels. Something is absorbing it, and ruining the UN projections of atmospheric CO2. Which also ruins UN temperature predictions.

Actually, all the factors in the UN temperature model are over-estimated, and thus their high temp predictions are not being achieved. Alarmists are working hard to create more dire theories and predictions.

Science is not accustomed to political bias, incentives to find certain types of results, bias in the selection of research topics and aims, bias in who gets the funding.

When all these conditions are present, as in climate research, we do not have normal science at work. We need to slow down and do basic research, and validate or reject the theories.

In the meantime, we must not tax away our prosperity, nor extinguish the energy which drives prosperity. Nor allow a world economy takeover by socialist greenies.
Caliban
2.6 / 5 (5) Nov 18, 2009
@3432682
Scientific research has ALWAYS been largely driven by the the biases you mention. Incredible that you should be so naive as to think otherwise.
Roderick
3 / 5 (4) Nov 18, 2009
3432682,

The UN temperature model has done quite well. You need to substantiate your claim instead of ranting and raving like Rush Limbaugh (a hero of yours?).
Wesch
5 / 5 (1) Nov 19, 2009
The article says:

Khatiwala and his colleagues came up with another method. Using some of the same data as their predecessors— seawater temperatures, salinity, manmade chlorofluorocarbons and other measures—they developed a mathematical technique to work backward from the measurements to infer the concentration of industrial carbon in surface waters, and its transport to deep water through ocean circulation. This allowed them to reconstruct the uptake and distribution of industrial carbon in the oceans over time.

We only have somewhat accurate seawater temperature measurements for the last half century or so. We have very little information about global salinity. Chlorofluorocarbons have only been made for half a century. Our understanding of the totality of ocean currents is low.

Could someone explain to me how they can use these to say how much carbon was absorbed by the ocean in say 1850 or 1920? Sounds like guesswork to me, not science.
po6ert
1 / 5 (1) Nov 19, 2009
higher acidity will lead to a change in flora and fauna. all the layer of limestone testify to the ability of organism to fix carbon more or less permantantly as calciaum carbonate. we live in an ice age. who is to say that this is not the result of excessive carbon sequestration?
jonnyboy
1 / 5 (3) Nov 19, 2009
@Wesch, you have got it exactly right. This is just another computer model designed to validate the same old "alarmist" BS the GW proponents have been trying to shove down our throats for years.

@gmurphy, almost every one of these AGW stories (they have the nerve to call them study's when they don't really sturdy anything) has a throw in phrase in the last paragraph(or two) covering their rear's in the event that the BS they publish is proven to be wrong.
GrayMouser
2.5 / 5 (2) Nov 26, 2009
@3432682
Scientific research has ALWAYS been largely driven by the the biases you mention. Incredible that you should be so naive as to think otherwise.

A bunch of it is stuffed shirts stoking their egos.
Another bunch is people getting off on poking holes in the stuffed shirts.
And some of it happens from people following a lead to it's end without regards to what their initial position was.

I like the last ones the best 8-)