Carbon Saturated Ocean
Air Date: Week of November 20, 2009
The Global Carbon Project just released its yearly carbon budget, and they’ve found that our current CO2 emissions put us on track to warm six degrees by 2100. New research suggests that the world’s oceans, responsible for absorbing a quarter of all our CO2 emissions, are maxing out and may not be able to keep soaking up our excess carbon. Host Jeff Young talks with Columbia University researcher Dr. Samar Khatiwala to ask about the ocean’s capacity to keep absorbing carbon dioxide.
YOUNG: From the Jennifer and Ted Stanley Studios in Somerville, Massachusetts - this is Living on Earth. I’m Jeff Young. Developments in both science and politics on climate change: The US and China agreed to cooperate on cleaner and more efficient forms of energy. But world leaders downplayed expectations about next month’s climate summit in Copenhagen. So political leaders sent mixed messages, but climate science sent a clear signal. The international scientists of the Global Carbon Project have a warning about the current trajectory of our CO2 emissions. Their new report, called the Global Carbon Budget, says we’re on a path towards a catastrophic 11 degrees Fahrenheit rise in the planet’s average temperature by the century’s end. Woods Hole Research Center director Richard Houghton helped write the Carbon Budget. He says it compiles the latest data on carbon sources and sinks.
HOUGHTON: We know we’re emitting carbon dioxide through burning fossil fuels and through deforestation. What we don’t know as well is where carbon is going. Only about half what we release stays in atmosphere. And the other half goes back into oceans or goes back into land.
YOUNG: Generally speaking, the sinks, the things that absorb carbon from the atmosphere – they’re not keeping pace with the emissions, it what you’re finding?
HOUGHTON: They’re not quite keeping up and that’s the worry. The point is that nature has been good to us and as these sinks get saturated or start to fill up they will not take up as large a fraction of what’s emitted.
YOUNG: Houghton’s report says natural storehouses of carbon have become slightly less efficient over the past 50 years or so – and two other new studies give us a deeper insight into one of the most important carbon sinks – the ocean. Oceans have been taking up close to a third of all the CO2 humans generate. But research in the current issue of the journal Nature suggests we’ve pushed the CO2 storage of the seas to the limit. Columbia University oceanographer Samar Khatiwala wrote that paper and he’s with us now - welcome to Living on Earth.
KHATIWALA: Thank you. Thanks for inviting me on your program.
YOUNG: Well, what did your study find about oceans and their ability to take up our CO2?
KHATIWALA: So, what we’ve discovered is that starting in about the 1950s or so, there was a really sharp increase in ocean CO2 uptake driven by the very explosive growth in emissions. That uptake is still increasing today, but at a slower pace, so that over time the oceans are absorbing a much smaller proportion of total human CO2 emissions. In fact, as much as ten percent less compared with just ten years ago.
YOUNG: So, just in the past decade it’s ten percent less compared to the emissions we’re putting out there?
KHATIWALA: Right, the proportion of emissions that the ocean takes up has gone down by about ten percent.
YOUNG: Even though the oceans are still absorbing more CO2 than I guess they ever have, right?
KHATIWALA: That’s correct. That, in absolute terms, the oceans are increasingly absorbing CO2. It’s currently about two point three billion tons per year.
YOUNG: Two point three billion tons, that’s how much the ocean is absorbing every year, is that right?
KHATIWALA: That’s correct. It represents about one fourth of total human CO2 emissions. Or to put it another way, it’s about six years worth of US gasoline consumption. So, it’s a very sizable sink for human CO2 emissions.
YOUNG: So, what is the ocean’s ability to absorb this CO2 lessening? What’s going on there?
KHATIWALA: The ocean circulation is really very sluggish, so if emissions grow too rapidly the ocean really can’t keep up. The other reason is what we like to call ‘ocean chemistry’. Basically, as CO2 dissolves in seawater, the ocean becomes more acidic and its capacity to take up more carbon in the future declines. So it’s really a combination of these two factors: ocean circulation and ocean acidification that’s combining to give this reduced uptake – relative uptake of ocean CO2.
YOUNG: So, essentially it’s just it can’t keep up with the emissions we’re pumping out there.
KHATIWALA: Exactly. That’s right. Almost everything, all the feedbacks between climate and the ocean are such that this problem can only get worse. You know, the ocean is only going to get more acidic, there’s nothing to prevent that. The ocean might warm up in the future, and that’s going to release, or make CO2 less soluble in water, for example. So, all these different factors together suggest that CO2 – relative CO2 uptake going into the future is going to decline.
YOUNG: That doesn’t bode well, does it?
KHATIWALA: Not in the long term. You know, in the short term, it’s a small change. But, once you start extrapolating into the future, it’s clearly going to be an important factor. If you look at that total amount of man-made carbon in the oceans at present, it’s about 150 billion tons of carbon, which if I want to put that into some kind of context, if you took all this carbon and you put it into the atmosphere, then atmosphere CO2 would be about 20 percent higher – or about 460 parts per million.
KHATIWALA: A lot of scientists think that if you want to abort sort of dangerous climate change, we should be limiting future CO2 to about 450 parts per million.
YOUNG: So, that chunk alone would already put us over right there?
KHATIWALA: Yeah. That would definitely put us over. So, the ocean is really doing its part in sort of preventing that from happening. You know, it’s giving us three or four decades of time so we can get our act together and hopefully reduce emissions.
YOUNG: So, I guess the takeaway lessons here is nature’s kind of been cutting us some slack. We’ve been pumping a lot of CO2 emissions up there and the oceans have been sucking a lot of it up, but we’re maxing out our account kind of here aren’t we?
KHATIWALA: That’s right. If you look at it as a carbon budget, then, yeah, we’ve been subsidized by the ocean and the land.
YOUNG: But the free lunch might be over?
KHATIWALA: That’s correct, yeah.
YOUNG: Professor Samar Khatiwala thanks very much.
KHATIWALA: Thank you for having me on your program.
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