Losing Nemo: Is There Time to Save the Seas?
Filed under: Discovery,News & Resources
Having compiled a high-level report on the state of the seas, released at the start of this month, Reid has been shocked by the news coming in from all quarters of marine science. “There are clear signs of accelerating change on all fronts, from physical to biogeochemical cycles to the role that biology plays,” he says.
James Lovelock’s Gaia hypothesis posited that the planet has homeostatic feedback loops that keep it within limits that suit life. Push the system too far, however, and those loops break like overstretched rubber bands. Given the quickening rate of change, fears are growing that we may already have broken them.
Richard Somerville, of the Scripps Institution of Oceanography in California, worked on the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC) in 2007, and in Copenhagen he will be delivering an update on what’s changed in the past two years. “The problem is that the planet keeps doing more than the IPCC said it would. The feedbacks are all going the other way,” he says. Rather than keeping things in check, they’re making them worse. When I ask if he thinks we have already passed a critical threshold, he pauses. “Tipping points are by their very nature unpredictable. In the end it’s a question of how lucky do you feel? Science can’t answer that.”
It was only in 2004 that the international scientific community, along with the IPCC, realised that Man’s carbon dioxide emissions had spawned not only climate change but an evil twin sister: ocean acidification. While the complexity of local weather and short-term climatic cycles can camouflage the glower of global warming, the simple chemistry of adding extra carbon dioxide to the ocean gives this new problem a grim predictability.
Dr Peter Brewer, chief scientist of the Monterey Bay Aquarium Research Institute in California, has been warning about ocean acidification since the 1970s, when no one would listen. “They said it was too small an effect, the data was too small and noisy. Besides, there was a feeling that the ocean would buffer the change, and that the uptake would be a good thing,” he says.
Taking all that carbon dioxide out of the air has meant the pH of the ocean has dropped by 0.1 since emissions began. That might not sound like much — pH is measured on a scale from 0 to 14, with things getting more acid as pH falls — but it represents a 30 per cent rise in acidity. The cascading range of impacts is jaw-dropping and expanding, as scientists project the ocean’s pH to drop by 0.4 by the end of the century, meaning acidity will be two-and-a-half times the present level.
Any creature with a shell is at risk. Among the best studied are the pteropods, sea snails the size of a child’s fingernail. In the cold Arctic waters where gases are most easily absorbed, by mid-century their shells will be pitting, peeling and dissolving. Once they are gone, what will replace them as a major food source for salmon, mackerel, herring, cod and baleen whales?
“Something else will grow in their place. It’s just that they may not support the ecosystems and food webs that we’re used to,” says Dr Carol Turley, of Plymouth Marine Laboratory, whose expertise on ocean acidification has earned her the nickname “the Acid Queen”. One of the things worrying her most is what will become of life in and on the seabed. “Organisms like starfish and urchins play a big part in the wider ecosystem. By removing shell-forming organisms, we’re removing the equivalent of earthworms, the bioengineers that stir up sediment and provide nutrients for new blooms,” she says. Without them, the power of the ocean to cycle carbon, nitrogen and other biogases would be hugely damaged.
The larval young of some marine animals are also in jeopardy, apparently unable to survive even a slight drop in pH. Those that do face another problem — the chemical signatures that larvae follow in order to find a suitable home will also be affected. Experiments on clownfish larvae show that they can no longer find a host anemone after just a small change in acidity. In the ocean of the future, finding Nemo may be an impossible task.
Although warm waters will be the last to suffer, for coral reefs, acidification will be the nail in their coffin. By the time carbon dioxide reaches 560 parts per million — projected to happen around 2050 — corals will be unable to grow their skeletons in 80 per cent of the ocean. As they start to dissolve, all the life they support will disappear with them. It would be the Earth’s sixth mass extinction, according to Charlie Veron.
With acidification now firmly on the scientific radar, Peter Brewer has turned his attention to another problem threatening the ocean. The concept is too new to have a catchy name, but it could be dubbed “the suffocating sea”.
It’s a brutally simple idea. Aerobic life — ourselves included — needs a certain ratio of carbon dioxide to oxygen in order to breathe. If you were trapped in a sealed room, it would not be the lack of oxygen that would kill you but the excess of carbon dioxide. The ratio gets increasingly skewed with depth.
In one part of the Pacific, 1,000 parts per million of CO2 at the surface becomes more than 2,500 parts per million 500 metres down, without there being much of a corresponding increase in oxygen.
As atmospheric CO2 levels continue to rise, the skeletal fingers of suffocation will reach steadily up out of the depths. One day they will meet low-oxygen regions that are already spreading, caused by the reluctance of well-oxygenated surface waters to mix with the colder, oxygen-poor waters below. “There is already clear evidence of expansion of the low-oxygen regions of the oceans,” Brewer recently wrote in the journal Science. “When these are combined with rising CO2 levels we will surely see true dead zones created.”
“The vast majority of animals are going to suffer badly,” he later admits. Things are a lot worse than they look.”
Faced with political inertia, scientists are scrambling to slow the ticking of the emissions time bomb. Veron knows only too well that the impacts on coral reefs are multiplying, not just adding up. While warming on its own might not kill a healthy reef, add overfishing, pollution or heavy sedimentation, and warming will surely see it off. The principle holds for other ocean ecosystems, so just as Veron is throwing his weight behind protecting the waters around the Great Barrier Reef and shielding it from fishing within a vast marine park, others are advocating similar ideas around the world.
But even an immediate halt to marine pollution and overfishing will not stop the timer. There is no James Bond-style fix for ocean acidification or suffocation. The only solution is to cut emissions of CO2.
Veron remains stubbornly optimistic. “Turning this around would be much less effort than a world war, and it’s much more serious. We have to attack this on all fronts, from grassroots to political. It doesn’t have to have a huge impact on human lives, but unless we do something it will. If ecosystems collapse then all else is irrelevant.”
A brittle star that lives in the eastern Atlantic seems to symbolise the plight of the oceans. It catches food by waving its arms in the current. When made to live in water whose chemistry matches that projected for 2100, the slender starfish spends all its energy just trying to grow the skeleton for its arms; it has no strength left to lift them, let alone wave.
