ACIDIFICATION THREATENS WORLD'S OCEANS

The rise in human emissions of carbon dioxide is driving fundamental and dangerous changes in the chemistry and ecosystems of the world's oceans, international marine scientists have warned in a study reported in ScienceDaily.

surface waters have already acidified an average of 0.1 pH units from pre-industrial levels, and we are seeing signs of its impact even in the deep oceans.

"Future acidification depends on how much CO2 humans emit from here on--but by 2100 various projections indicate that the oceans will have acidified by a further 0.3 to 0.4 pH units, which is more than many organisms like corals can stand," says co-author, Prof. Hoegh-Guldberg of the ARC Centre of Excellence for Coral Reef Studies and The University of Queensland. "This will create conditions not seen on Earth for at least 40 million years. These changes are taking place as much as 100 times faster than they ever have over the last tens of millions of years."

Under such circumstances, "Conditions are likely to become very hostile for calcifying species in the north Atlantic and Pacific over the next decade and in the Southern Ocean over the next few decades," the researchers warn.

Besides directly impacting on the fishing industry and its contribution to the human food supply at a time when global food demand is doubling, a major die-off in the oceans would affect birds and many land species and change the biology of Earth as a whole profoundly, Prof. Hoegh-Guldberg adds.

The scientists say there is now persuasive evidence that mass extinctions in past Earth history, like the "Great Dying" of 251 million years ago and another wipeout 55 million years ago, were accompanied by ocean acidification, which may have delivered the deathblow to many species that were unable to cope with it.

"These past periods can serve as great lessons of what we can expect in the future, if we continue to push the acidity the ocean even further" said lead author, Dr. Carles Pelejero, from ICREA and the Marine Science Institute of CSIC in Barcelona, Spain.