The shell specimens dated back to 1996 and the earlier ones had weighed in at 20 micrograms. But Roberts observed that as the specimens became more recent, the weight of the shells had fallen. When her last specimen, from 2005, weighed in at just 10 micrograms, Roberts barely dared to breathe. "Wow, what is going on?" she asked herself. A halving of shell weight in just one decade was a real worry.

Roberts's still unpublished research is just one reason why her collaborator, Dr Will Howard, from the Antarctic Climate and Ecosystems Cooperative Research Centre, this week convened an extraordinary meeting of Australia's leading marine scientists in Hobart. For three days, the 50 scientists, along with colleagues from America and New Zealand, focused their collective minds on a threat that has emerged, it seems, from out of the blue: the growing acidification of our oceans. These scientists now know that burning fossil fuels and massive land clearing are not just warming the planet and raising sea temperatures, they are also changing the chemical make up of the oceans. A vast amount of the carbon dioxide humans have pumped into the atmosphere since the industrial revolution has been absorbed by oceans.

A new report by the Antarctic research centre, released at the Hobart meeting, says that about half the fossil fuel carbon dioxide released into the atmosphere by humans has now dissolved into the oceans. If we keep pumping carbon dioxide into the atmosphere at the current projections, by 2100 the ocean acidification will be three times that experienced at the end of the glacial period, 15,000 years ago. The chemistry is basic. The ocean is a weakly alkaline solution. When carbon dioxide sucked in from the atmosphere dissolves in sea water, it forms a weak acid, making the ocean more acidic. For sea life with fragile shells, corals and countless other sea creatures, a more acidic ocean could be disastrous and have unknown impacts right up the marine food chain.

"It's going to affect every part of Australia's marine environment, every bit of water that's in contact with the atmosphere," Howard told the Herald. "If I could sit Kevin Rudd down tomorrow, I would say: this is an inevitable and inexorable consequence of our putting carbon dioxide into the atmosphere. It's not going to stop. What we need to do quickly is get some research together where you can anticipate the ecological impacts of this." So concerned were scientists at the meeting they decided to launch a Hobart declaration on ocean acidification. While their final communique is being thrashed out, all present were alarmed by the growing evidence that the oceans are changing, with consequences so far immeasurable for marine life. Using the most basic calculation, Australia controls some 8 million square kilometres of ocean. Those waters generate about $52 billion in national wealth, according to the CSIRO, including a $2.5 billion fishing industry, and vast tourism dollars. Just as valuable is the extraordinary array of marine life that protects the coastlines, supports the reefs, and stops algae from choking the beaches.

What the scientists are asking is this: how quickly will the oceans reach the point where some vital sea creatures will not survive? How many will be able to adapt to the new conditions? What happens to all this marine life when rising acid levels combine with the rising sea temperatures caused by global warming? Right now, the best predictions are that within 50 to 60 years, a serious rise in ocean acidification is likely to leave some species struggling to survive, especially corals and creatures with fragile shells.

"There are distinct chemical thresholds and once they are crossed, these organisms' shells would tend to dissolve," Howard explains. "As the ocean approaches those thresholds, the organisms' ability to make those shells are compromised. There is a zero sum game." Australian marine scientists working in the Southern Ocean now unexpectedly find themselves on the front lines in this new crisis. For a range of complex reasons, the impacts of ocean acidification are expected to be felt first in the deep, cold, Antarctic waters, which will become a giant lab lesson for the rest of the world. One of these frontline scientists is Dr Martin Riddle, a marine biologist with the Australian Antarctic Division. Back in December, Riddle and his team made an extraordinary discovery off the Antarctic coast near the Mertz Glacier. Between 600 and 800 metres underwater they came upon a stunning cold water coral community as colourful as anything on the Great Barrier Reef. "We were blown away by it," Riddle recalled.

The discovery made news around the world, but Riddle believes it might one day return to the headlines for quite different reasons than its beauty. Rising acidification of the Southern Ocean is likely to overtake the beautiful reef in 50 to 60 years. "This could be a dramatic change that nobody but me would have known about," says Riddle. "If we hadn't gone down to find it, we wouldn't have even known about it. But it's really the canary in the cage. It's the early warning system. Ocean acidification is going to affect cold, deep areas first. They will indicate what is likely to happen elsewhere into the future. That is really the importance of this particular site."

If the bottom of the food chain around reefs like this begins to change, he explains, we will see changes in the rest of the food chain. "Does it worry me? Of course it does." Disturbing findings about the impacts of acidification - some definite, many preliminary - were debated at the Hobart meeting. A series of early lab tests on krill, a vital food source for the Southern Ocean whale population, found that as acid levels rose krill kept reproducing, but the offspring developed deformities. While the research is incomplete and inconclusive, it underscored anxiety about Australia's need for a major research effort to grasp the enormity of the problem. Professor Maria Byrne, from Sydney University, warned that ocean acidification must be examined in tandem with climate change, especially rising sea temperatures, because the most damage to marine life would come from a combination of stresses.

Last year, CSIRO researchers reported Australia's southern east coast could be hardest hit by global warming, with sea temperatures rising by up to two degrees by 2070. East of Tasmania, sea temperatures are already rising faster than the global average, increasing by more than two degrees since the 1940s. "We know NSW is a global climate change hot spot," says Byrne. "If you look … from Cape Byron all the way down to Tasmania, you'll see the red on the map of the CSIRO climate change model."

Byrne had previously examined the impacts on sea urchins,"the cows of the sea" that keep NSW shores free of algae. First, she heated their water to 24 degrees, equivalent to the hottest contemporary NSW summer sea temperature. The sea urchins survived OK. But when she raised the water temperature to 26 degrees, things quickly went bad. "I got a 75 per cent mortality rate. The embryos started to die after three days." And when Byrne added a higher acid level to the water, all hell broke loose. "It's the two stresses together," she said. "It caused massive mortality within hours." Five years ago, almost no prominent scientist in Australia was talking about ocean acidification, including those who worked on the peak United Nations scientific body, the Intergovernmental Panel on Climate Change. Indeed, the panel devoted just one line to the topic in its Nobel Prize-winning report. That is now rapidly changing.

A bill was introduced last year to the US Senate for a $US30 million ocean acidification research program. Next week, a similar European project will be launched. The Australian scientists, led by Howard and the CSIRO's Dr Bronte Tilbrook, hope to galvanise political and community support behind a national research effort to help not only Australia but the whole South Pacific region adapt to a profound and enduring change to marine life.

Even if carbon dioxide emissions are radically reduced now, Howard and Tilbrook explain, the oceans will take hundreds of years to recover. But right now, the biggest cause for concern, says Howard, is that it is starting to look like some of the changes are happening much faster than anyone anticipated.