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Scientists reveal excess atmospheric carbon dioxide causes rapid ocean acidification, threatens species

By Fiona Harvey, The Guardian
Sunday, August 25, 2013 16:52 EDT
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Experts claim current rate of change is likely to be more than 10 times faster than it has ever been in Earth’s history

Rapidly rising carbon dioxide levels in the atmosphere are causing a potential catastrophe in our oceans as they become more acidic, scientists have warned.

Hans Poertner, professor of marine biology at the Alfred Wegener Institute in Germany, and co-author of a new study of the phenomenon, told the Guardian: “The current rate of change is likely to be more than 10 times faster than it has been in any of the evolutionary crises in the earth’s history.”

Seawater is naturally slightly alkaline, but as oceans absorb CO2 from the air, their pH level falls gradually. Under the rapid escalation of greenhouse gas emissions, ocean acidification is gathering pace and many forms of marine life – especially species that build calcium-based shells – are under threat.

Poertner said that if emissions continue to rise at “business as usual” rates, this would be potentially catastrophic for some species. Acidification is just one of a broader range of the problems facing the oceans and the combination of different effects is increasing the threat. Poertner said: “We are already seeing warm water coral reefs on a downslide due to a combination of various stressors, including [rising] temperature. Ocean acidification is still early in the process [but] it will exacerbate these effects as it develops and we will see more calcifying species suffering.”

However, the process of acidification takes decades and the worst effects on some species could still be avoided if emissions are urgently reduced. “The ocean is changing already, mostly due to temperature – acidification will exacerbate those effects,” Poertner said.

Evidence from prehistoric ocean life provides a comparison. “The [effects observed] among invertebrates resembles those seen during the Permian Triassic extinctions 250m years ago, when carbon dioxide was also involved. The carbon dioxide range at which we see this sensitivity [to acidification] kicking in are the ones expected for the later part of this century and beyond.”

Oceans are one of the biggest areas of focus for current climate change research. The gradual warming of the deep oceans, as warmer water from the surface circulates gradually to lower depths, is thought to be a significant factor in the earth’s climate. New science suggests that the absorption of heat by the oceans is probably one of the reasons that the observed warming in the last 15 years has been at a slightly slower pace than previously, and this is likely to form an important part of next month’s Intergovernmental Panel on Climate Change (IPCC) report.

The IPCC report, the first since 2007, will provide a comprehensive picture of our knowledge of climate change. It is expected to show that scientists are at least 95% certain that global warming is happening and caused by human activity, but that some uncertainties remain over the exact degree of the planet’s sensitivity to greenhouse gas increases.

The new study, entitled Inhospitable Oceans, published on Monday in the peer-review journal Nature Climate Change, was based on examinations of five key components of ocean eco-systems: corals, echinoderms, molluscs, crustaceans and fish. All were found to be adversely affected by acidification: crustaceans were more resilient, while corals, molluscs and echinoderms were worst affected. The direct effects on fish were less clear.

Astrid Wittmann, co-author of the paper, said species with low resilience could be outcompeted by those that were more vulnerable to acidification, and that further studies were needed, particularly on plants and plankton, which were left out of this research.

guardian.co.uk © Guardian News and Media 2013

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