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Wednesday, September 23, 2020
BROOKLIN, Canada, Nov 12 2007 (IPS) - Coral reefs face certain extinction in a few decades unless there are unprecedented reductions in carbon emissions, leading Australian scientists warn.
The reason? Rising carbon dioxide (CO2) levels in the atmosphere are turning the oceans acidic far faster than previously observed.
“It isn’t just the coral reefs which are affected. A large part of the plankton in the Southern Ocean, the coccolithophorids, are also affected,” said Malcolm McCulloch, an environmental research scientist at the Australian National University in Canberra.
“These (coccolithophorids) drive ocean productivity and are the base of the food web which supports krill, whales, tuna and our fisheries,” McCulloch said in a statement.
Plankton also play a vital role in removing carbon dioxide from the atmosphere and sequestering it in the deep ocean. Major declines in plankton mean atmospheric CO2 levels would rise far faster than the present forecasts and oceans would become even more acidic.
“This is still early days for the research, and the trend is not uniform, but it certainly looks as if marine acidity is building up,” said McCulloch.
The oceans and the atmosphere are intimately connected – the quintessential yin and yang. Changes in the atmosphere affect the oceans and vice-versa. Pump extra CO2 into the atmosphere from burning fossil fuels and some of that extra CO2 combines with carbonate ions in seawater, forming carbonic acid. The fact that CO2 is making the oceans more acid was established just three years ago. Scientists are still scrambling to determine the overall impacts.
“The effect of an acidifying ocean is that precious carbonate ions are removed,” says Ove Hoegh-Guldberg, a scientist at the Centre for Marine Studies at the University of Queensland, Australia.
“These ions are critical to the calcium carbonate production (calcification) of a range of marine organisms, including reef-building corals,” Hoegh-Guldberg told IPS.
Hoegh-Guldberg, McCulloch and more than 50 marine scientists attending a recent forum hosted by Australian Research Council Centre of Excellence for Coral Reef Studies have released a formal call to action, calling on “all societies and governments to immediately and substantially reduce greenhouse gas emissions”.
“Ocean acidification due to increased atmospheric CO2 is accelerating…Reducing CO2 emissions is the only way to prevent further damage to coral reefs,” they warn.
As carbon dioxide increases in the atmosphere, the concentration of carbonate ions declines, with the result that corals can no longer build reefs. The oceans have already absorbed nearly half of the fossil-fuel CO2 emitted into the atmosphere since pre-industrial times, causing a significant reduction in seawater pH.
“And with no reef framework, the habitat for an estimated million species is destroyed,” Hoegh-Guldberg said.
Reefs are not only spectacular-looking habitats, they are the world’s largest living organisms easily visible from space. Their economic and biological importance is staggering. While occupying less than one percent of the oceans, they are home to or a vital resource for 25 to 33 percent of the oceans’ creatures. The World Conservation Union (IUCN) considers coral reefs one of the life-support systems essential for human survival.
In island nations where agricultural land is limited, fisheries are the primary source of protein and, often, the only source of income, said Simon Donner, a researcher at Princeton University studying the impacts of climate change.
Australia’s 2,000-km-long Great Barrier Reef attracted over six billion dollars in international tourist income in 2006 alone.
And the half billion people or so that depend on reefs are the least responsible for fossil fuel emissions, emitting less than ten percent of the average U.S. citizen, he told IPS.
Climate change is also raising ocean temperatures, which has resulted in coral bleaching. Last year, warm waters resulted in significant damage to the Great Barrier Reef. In 2005, the corals in the Caribbean suffered an unprecedented die-off from very warm waters.
Reefs can often recover from bleaching if they are healthy to begin with and water temperatures cool. However, recovery will not be possible if CO2 levels rise to 500 ppm (parts per million) because there will not be enough carbonate ions left in the oceans for corals to grow, says Hoegh-Guldberg.
At that point, reefs will be transformed from being “thriving ecosystems into marine deserts”.
That shocking scenario may only be decades away based on the current business-as-usual model of ever increasing use of coal, oil and fossil fuels, as forecast last week by the International Energy Agency (IEA).
The IEA estimates that fossil fuel emissions will rise 57 percent by 2030, at which point CO2 levels are very likely to be in the 450 to 500 ppm range, some experts suggest.
Even the best case scenario of massive cuts in emissions, and achieving the Intergovernmental Panel on Climate Change (IPCC) goal of CO2 stabilisation at 500 ppm by 2050, may simply delay the demise of reefs by another 20 years.
The crisis is here. Going beyond 500 ppm is not an option, it invites catastrophe, says Hoegh-Guldberg.
This a new finding and not everyone agrees.
“I don’t think 500 ppm is the critical threshold,” Ulf Riebesell, a scientist at Leibniz Institute of Marine Sciences in Kiel, Germany told IPS.
Riebesell’s own work in Norway’s cold fjords, published in the magazine Nature Nov. 11, shows that increased levels of CO2 spark plankton blooms in the oceans and may substantially increase the oceans’ ability to absorb carbon from the atmosphere. It would accelerate the existing biological conveyor belt where plankton and the carbon they absorb sink to the bottom of the sea.
If his finding plays out in all parts of the world’s oceans, that would be very good news, slowing the rate of CO2 build-up in the atmosphere. However, there are still likely to be impacts on the oceans. Riebesell worries that all that extra carbon in the deep ocean will turn it acidic – currently only the top layer is being affected.
Another impact may be the creation of large oxygen-deficient areas, or dead zones. When plankton blooms die, they take oxygen from the water, creating vast areas where little can live, as happens currently in the Gulf of Mexico.
Riebesell did not look at impacts on corals, but says that the decline in calcification the Australians have found will affect shell-forming phytoplankton and could slow this biological conveyor that takes carbon into the deep ocean. But that is the subject of intense debate.
“I am certain that scientists will discover further biological feedback mechanisms in the near future,” he says.
It also may also be that by the time carbon dioxide levels are high enough to stop reef building, most of the world’s corals will have been killed by bleaching because the oceans have warmed significantly.
“If you are a coral, pick your poison,” observes Donner.
“The threat to coral reefs is so great, so existential, that you are seeing even the most cautious, reticent scientists shouting from the rooftops,” he says.
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