Ocean study: 'Mass extinction event may already be underway'

October 18, 2013
The combined effects of acidification and ocean warming will seal the fate of the world's coral reefs.

Mainstream media outlets gave substantial coverage to the UN’s new report on the climate change crisis late last month, which said the Earth’s climate is warming faster than at any point in the past 65 million years and that human activity is the cause.

Disappointingly, though not unsurprisingly, the news reports dried up after only a few days.

But another major scientific study, released a week later and including even graver warnings of a global environmental catastrophe, was mostly ignored.

The marine scientists that released the State of the Ocean 2013 report on October 3 gave the starkest possible warning about the impact of carbon pollution on the oceans. They said: “We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure. The next mass extinction event may have already begun.

“Developed, industrialised human society is living above the carrying capacity of the Earth, and the implications for the ocean, and thus for all humans, are huge.”

Report co-author Professor Alex Rogers of Somerville College, Oxford, said on October 3: “The health of the ocean is spiralling downwards far more rapidly than we had thought. We are seeing greater change, happening faster, and the effects are more imminent than previously anticipated.

“The situation should be of the gravest concern to everyone since everyone will be affected by changes in the ability of the ocean to support life on Earth.”

The ocean is by far the Earth’s largest carbon sink and has absorbed most of the excess carbon pollution put into the atmosphere from burning fossil fuels. The State of the Ocean 2013 report warned that this is making decisive changes to the ocean itself, causing a “deadly trio of impacts” — acidification, ocean warming and deoxygenation (a fall in ocean oxygen levels).

The report said: “Most, if not all, of the Earth’s five past mass extinction events have involved at least one of these three main symptoms of global carbon perturbations [or disruptions], all of which are present in the ocean today.”

Fossil records indicate five mass extinction events have taken place in the Earth’s history. The biggest of these — the end Permian mass extinction — wiped out as much as 95% of marine life about 250 million years ago. Another, far better known, mass extinction event wiped out the dinosaurs about 66 million years ago and is thought to have been caused by a huge meteor strike.

Another big species extinction took place 55 million years ago. Known as the Paleocene/Eocene thermal maximum (PETM), it was a period of rapid global warming associated with a huge release of greenhouse gases. “Today’s rate of carbon release,” said the State of the Ocean 2013 report, “is at least 10 times faster than that which preceded the [PETM].”

Ocean acidification is a sign that the increase in CO² is surpassing the ocean’s capacity to absorb it. The more acid the ocean becomes, the bigger threat it poses to marine life — especially sea creatures that form their skeletons or shells from calcium carbonate, such as crustaceans, molluscs, corals and plankton.

The report predicts “extremely serious consequences for ocean life” if the release of CO² does not fall, including “the extinction of some species and decline in biodiversity overall”.

Acidification is taking place fastest at higher latitudes, but overall the report says “geological records indicate that the current acidification is unparalleled in at least the last 300 million years”.

Ocean warming is the second part of the “deadly trio”. Average ocean temperatures have risen by 0.6°C in the past 100 years. As the ocean gets warmer still, it will help trigger critical climate tipping points that will warm the entire planet even faster, hurtling it far beyond the climate in which today’s life has evolved.

Ocean warming will accelerate the death spiral of polar sea ice and risks the “increased venting of the greenhouse gas methane from the Arctic seabed”, the report says.

Ongoing ocean warming will also wreak havoc on marine life. The report projects the “loss of 60% of present biodiversity of exploited marine life and invertebrates, including numerous local extinctions”.

Each decade, fish are expected to migrate between 30 kilometres and 130 kilometres towards the poles, and live 3.5 metres deeper underwater, leading to a 40% fall in fish catch potential in tropical regions.

The report says: “All these changes will have massive economic and food security consequences, not least for the fishing industry and those who depend on it.”

The combined effects of acidification and ocean warming will also seal the fate of the world’s coral reefs, leading to their “terminal and rapid decline” by 2050. Australia’s Great Barrier Reef and Caribbean Sea reefs are likely to “shift from coral domination to algal domination”.

The report says the global target to limit the average temperature rise to 2°C, which was adopted at the Copenhagen UN climate conference in 2009, “is not sufficient for coral reefs to survive. Lower targets should be urgently pursued.”

Deoxygenation — the third prong of the “deadly trio” — is related to ocean warming and to high levels of nutrient run-off into the ocean from sewerage and agriculture. The report says overall ocean oxygen levels, which have declined consistently for the past five decades, could fall by between 1% and 7% by 2100. But this figure does not indicate the big rise in the number of low oxygen “dead zones”, which has doubled every decade since the 1960s.

Whereas acidification mostly impacts upon smaller marine life, deoxygenation hits larger animals, such as Marlin and Tuna, hardest.

The State of the Ocean 2013 report cautions that the combined impact of this “deadly trio” will “have cascading consequences for marine biology, including altered food webs dynamics and the expansion of pathogens [causing disease]”. It also warns that it adds to other big problems affecting the ocean, such as chemical pollution and overfishing (up to 70% of the world’s fish stock is overfished).

“We may already have entered into an extinction period and not yet realised it,” the report said.

“What is certain is that the current carbon perturbations will have huge implications for humans, and may well be the most important challenge faced since the hominids evolved. The urgent need to reduce the pressure of all ocean stressors, especially CO² emissions, is well signposted.”

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