Oceans of acid

As global warming wreaks havoc on coral reefs, evidence is mounting that another problem caused by carbon dioxide is an even bigger threat. But is it too late to fix?

It’s six o’clock on a Sunday morning and I’m sitting on Queensland’s Four Mile Beach. There’s still a night chill to the air. Though the light is dim, a red glow is building on the horizon as the Sun is about to emerge from beyond the Pacific Ocean.

I’m playing with the sand between my toes and fiddling with a small piece of coral rubbed smooth by the tide.

I’ve spent the preceding few days out on an Australian government marine survey vessel snaking its way along the Great Barrier Reef. The trip has given me a lot to think about, both good and bad, and this morning I’m mulling over everything I’ve experienced.

In late July, the CSIRO invited me to join a team of 14 scientists, led by oceanographer Bronte Tilbrook and climate modeller Richard Matear, as they collected data to predict the future health of the reef.

The issue on their agenda is ocean acidification, commonly referred to by those in the know as “the other CO2 problem” – separate, but linked to climate change. Though acidification has had a lot less press, there is mounting evidence to suggest that it will be a bigger problem for marine life than the warming of the oceans themselves.



Our waste carbon dioxide (CO2) is mostly maligned for causing climate change as it builds up in the atmosphere, trapping heat, but for the past 200 years it’s also been quietly dissolving into the oceans, slowly making them more acidic.

In fact, the oceans are in equilibrium with the atmosphere and have been credited with absorbing something like 40 per cent of all the CO2 we’ve pumped out in the last 200 years. In this way, they have acted as a useful brake on global warming, but experts have slowly come to realise that this service has come at a terrible price.

“The oceans have this huge buffering potential for CO2, and until around a decade ago we thought there was plenty of capacity left and [CO2 dissolving] wouldn’t have a big effect,” says Tilbrook, a tall man with white hair, pale blue eyes and a gentle disposition. But research in the 1990s on corals and early maps of oceanic CO2 concentrations painted a very different picture.

The problem was neatly illustrated by an accidental discovery made more than a decade ago by Victoria Fabry, a biologist at California State University in San Marcos, USA. While out on another research cruise, Fabry found that something strange was taking place in sealed jars of seawater populated with shelled planktonic organisms called pteropods. After a few days the shells of the pteropods started to look thinner, and eventually dissolved.

The reason, Fabry realised, was that CO2 from respiration was building up in the jars, dissolving in the seawater as a weak solution of carbonic acid, and drastically reducing the availability of calcium carbonate (the major constituent of limestone or chalk), which many marine animals need to build their skeleton or shells.

“As CO2 levels rise in the ocean it makes the actual chemical formation of calcium carbonate difficult for organisms,” says Matear, a Canadian lured over to Australia by the CSIRO in the 1990s. “The important thing here is that … the calcium carbonate becomes a little less stable and corals seem to calcify less.”

Joanie Kleypas, based at the U.S. National Centre for Atmospheric Research (NCAR) in Boulder, Colorado, was one of a handful of scientists to realise there was a problem. In the late ’90s, she battled tirelessly to have the research community accept their conclusions.

She explains to me via email that, while warming of the oceans will swiftly kill coral outright through bleaching, ocean acidification will work by hindering recovery. “Increasing atmospheric CO2 is like an underlying disease that causes two different kinds of symptoms,” she says. “One is acute, like a heart attack, and the other is chronic, like osteoporosis.”

The difference in pH we’re talking about seems trifling, but it is enough to have a profound effect on life. Pure water is neutral with a pH of around 7. Seawater is slightly alkaline, and for millions of years has been a fairly constant pH 8.2. But already dissolved CO2 has reduced that to 8.05, and as carbon continues to build up in the atmosphere, it’s going to drop much further.

If projections are correct, an additional drop in pH of 0.4 by the end of this century will be “well outside the realms of anything organisms have experienced in over hundreds of thousands of years,” says Janice Lough, a climate scientist with the Australian Institute of Marine Science, in Townsville, Queensland.

John Pickrell, COSMOS, December 2008. Full article.

2 Responses to “Oceans of acid”


  1. 1 Jean-Pierre Gattuso 6 February 2009 at 11:18

    The title of this article is unfortunate because, as mentioned in the body of the article, the oceans are alkaline and will not become acidic (pH lower than 7) even in the distant future.

  2. 2 jim hackman 25 February 2009 at 16:54

    The oceans will never become acid, ever, I am begining to think all you people don’t know the first thing about chemistry. Please tell me how much carbon it would take to turn the oceans of the world acid , you seem bright enough to predict the future what is the exact tonnage of co2 needed to get below a ph of 7. You can’t acheive more acidic ,you only can get less basic until you get under 7.0
    I lived in the florida keys I swam with the coral you are worried about for years ,never saw bleached coral , because the temperature of the water is not increasing there and as it is not increasing anywhere around the u.s.a. Look at the noaa bouy data it is all there 30 years of data I challenge you to show me one bouy station that shows a temperature increase over the last ten years that has stayed constant.


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