The oil spill in the Gulf of Mexico is a disaster, but it may pale compared to what scientists say is brewing in the world's oceans due to everyday consumption of fossil fuels.
The billions of tonnes of carbon dioxide sent wafting into the atmosphere each year through the burning of oil, gas and coal are profoundly affecting the oceans, says a series of reports published Friday in the journal Science.
One says there is mounting evidence that "rapidly rising greenhouse gas concentrations are driving ocean systems toward conditions not seen for millions of years, with an associated risk of fundamental and irreversible ecological transformation."
Another says that the effects are already rippling through the food web in Antarctica.
And a third says humans, and their ever-increasing carbon emissions, are acidifying the ocean in a "grand planetary experiment" that could have devastating impacts.
Marine scientists Ove Hoegh-Guldberg, at the University of Queensland in Australia, and John Bruno, at University of North Carolina, describe how the oceans act as a "heat sink" and are slowly heating up along with the atmosphere as greenhouse gas emissions climb.
The warming, they say, is "likely to have profound influences on the strength, direction and behaviour" of major ocean currents and far-reaching impacts on sea life.
The oceans also soak up close to a third of the carbon dioxide that humans put into the atmosphere and it reacts with sea water to form acidic ions. The rising acidity "represents a major departure from the geochemical conditions that have prevailed in the global ocean for hundreds of thousands, if not million of years," the scientists report.
Add it all up and they say there is there is "overwhelming" evidence human activities are driving changes on a scale similar to volcanic eruptions or meteorite strikes, which have driven ecosystems to collapse in the past.
"The impacts of anthropogenic (human) climate change so far include decreased ocean productivity, altered food web dynamics, reduced abundance of habitat-forming species, shifting species distributions and a greater incidence of disease," they say.
In a second report, Oscar Schofield at Rutgers University, and his colleagues describe how rising temperatures over the last 30 years have coincided with a shift in the food web along the West Antarctic Peninsula — most notably to a shrinking of marine algae cells. Organisms known as tunicates are so efficient at feeding on the smaller algae they appear to be displacing krill, a mainstay of many creatures up the food web. Fish, seals, whales, penguins and other seabirds could all be affected, they say.
A news report, accompanying the Science papers on the oceans, says by increasing the ocean's acidity "humans are caught up in a grand planetary experiment" that could take a "potentially devastating toll on marine life." The rising acidity could erode the calcium carbonate shells and skeletons of corals, mollusks and some algae and plankton — and there is some evidence it is already starting to occur.
"The physics and chemistry of adding an acid to the ocean are so well understood, so inexorable, that there cannot be an iota of doubt — gigatons of acid are lowering the pH of the world ocean, humans are totally responsible, and the more carbon dioxide we emit, the worse it's going to get," it says.
It goes on to quote a recent issue of the journal Oceanography that said unconstrained growth of emissions is likely to leave the current era of human planetary dominance "as one of the most notable, if not cataclysmic, events in the history of our planet."
