Jason Hall-Spencer thinks he has seen the future of the world’s oceans while diving at marine volcanic sites around the world, where jets of carbon dioxide fizz out of vents on the sea floor.

Most scientists use computer models or laboratory experiments to try and predict how the oceans will change because of the growing amount of carbon dioxide being absorbed from the atmosphere.

But Dr. Hall-Spencer, an associate professor at the School of Marine Science and Engineering at the University of Plymouth, in the United Kingdom, said he thinks the best way is to dive on volcanic vents, where carbon dioxide is naturally injected into the ocean.

“It’s like a time machine looking into the future of how the oceans are going to acidify,” he said at the annual conference of the American Association for the Advancement of Science, which is under way in Vancouver this weekend.

“What I’m doing is a bit different to what most people do, in that I’m looking at the effects of carbon dioxide release on the sea bed naturally, and using this as giant laboratories to see how ecosystems are affected,” he said.

Dr. Hall-Spencer said researchers can only look at one species at a time in a lab, but he has entire, complex ecosystems to study around volcanic, carbon-dioxide vents.

He said by proceeding along a gradient on the sea floor it is possible to move from slightly acidic, to intensely acidic ocean environments.

“If you roll into the water at these vent systems you see this Jacuzzi of bubbles. That’s the carbon dioxide. And what you can do is you pick somewhere along the gradient that reflects what it’s going to be like in five years time, or 10 years time, or 50 years time, and see the effect of ocean acidification on the entire system. That’s almost impossible to do in laboratory settings,” said Dr. Hall-Spencer.

“And what we notice unfortunately is this very dramatic shift in the ecosystem. There’s a tipping point that occurs about the levels of ocean acidification we expect to see at the end of this century,” he said.

“As you increase CO2, to the levels that we predict for this century, you get a 30-per-cent drop in the biodiversity, not only of microbes, but also of all the plants and all the animals, from corals to fish. So, it’s just not good.”

Dr. Hall-Spencer said many species are under apparent stress because the carbon dioxide has made the sea corrosive, and then it just takes a slight increase in temperature to push them over the edge.

“It’s like us panting for oxygen at high altitude. They are struggling. And in the summer when the temperatures are high, these organisms that are struggling just die.

“And that’s very problematic because of course carbon dioxide not only acidifies sea water, but it’s increasing the temperature of the atmosphere. Those two things combined are a double whammy,” he said.

Dr. Hall-Spencer drew a link between the Alberta oil sands project and the environmental problems he sees on the sea floor.

“Digging up things like the tar sands of Canada is a really bad environmental idea,” he said. “We can’t stop the sea becoming acidified by this CO2 that’s already up there [in the atmosphere]. But what we can do . . is reduce the amount of CO2 that we’re putting into the atmosphere now.”

Another member of an oceans panel at the AAAS conference, Gretchen Hoffman, professor of marine biology at University of California at Santa Barbara, said the polar seas might be the first areas devastated by ocean acidification.

She said because cold water tends to hold more gas, the Arctic and Antarctic oceans already contain more carbon dioxide than other areas.

Dr. Hoffman said some oceanographers are predicting that by 2030 the Antarctic ocean could reach a point where it is impossible for some key organisms to survive.

“They are already on the hairy edge. They’ll probably be the first to cross the line,” she said of the polar seas.