The largest living structures on Earth and the millions of livelihoods which depend upon them are at risk, the most definitive review yet of the impact of rising carbon emissions on coral reefs has concluded.
If world leaders do not immediately engage in a race against time to save the Earth's coral reefs, these vital ecosystems will not survive the global warming and acidification predicted for later this century. That is the conclusion of a group of marine scientists from around the world in a major new study published in the journal Science on Dec. 13.
"It's vital that the public understands that the lack of sustainability in the world's carbon emissions is causing the rapid loss of coral reefs, the world's most biodiverse marine ecosystem," said Drew Harvell, Cornell professor of ecology and evolutionary biology and head of the Coral Disease Research Team, which is part of the international Coral Reef Targeted Research (CRTR) group that wrote the new study.
The rise of carbon dioxide emissions and the resultant climate warming from the burning of fossil fuels are making oceans warmer and more acidic, said co-author Harvell, which is triggering widespread coral disease and stifling coral growth toward "a tipping point for functional collapse."
The scientists argue that rising global CO2 emissions represent an 'irreducible risk' that will rapidly outstrip the capacity of local coastal managers and policy-makers to maintain the health of these critical ecosystems, if CO2 emissions are allowed to continue unchecked.
"This crisis is on our doorstep, not decades away. We have little time in which to respond, but respond, we must!" says Professor Ove Hoegh-Guldberg, lead author of the Science paper, The Carbon Crisis: Coral Reefs under Rapid Climate Change and Ocean Acidification.
"Coral reefs have already taken a big hit from recent warm temperatures, but rapid rises in carbon dioxide cause acidification, which adds a new threat: the inability of corals to create calcareous skeletons," said Harvell. "Acidification actually threatens all marine animals and plants with calcareous skeletons, including corals, snails, clams and crabs. Our study shows that levels of CO2 could become unsustainable for coral reefs in as little as five decades."
"The livelihoods of 100 million people living along the coasts of tropical developing countries will be among the first major casualties of rising levels of carbon in the atmosphere," says Professor Hoegh-Guldberg.
"The warmer and more acidic oceans caused by the rise of carbon dioxide from the burning of fossil fuels threaten to destroy coral reef ecosystems, exposing people to flooding, coastal erosion and the loss of food and income from reef-based fisheries and tourism. And this is happening just when many nations are hoping that these industries would allow them to alleviate their impoverished state."
Coral reefs are often portrayed as natural wonders of great beauty which makes them an important tourism attraction. In Australia, revenue from international tourism to the Great Barrier Reef exceeds $6.8 billion per year. It is estimated that coral reef-related tourism generates tens of billions of dollars per year worldwide. They are the economic engine of a vast number of economies around the world.
Professor Hoegh-Guldberg, who is based at The University of Queensland, says coral reefs occupy a unique niche in the world's environment, where water temperatures and other environmental factors are 'just right'. "But raising as little as 1°C the temperature that ocean surface waters reach in summer subjects coral reefs to stresses which lead quickly to mass bleaching. Raise the temperature a little more, and the corals that build reefs die in great numbers. No coral, no coral reef ecosystem," says Professor Hoegh-Guldberg.
"In summary, the environment that has surrounded coral reefs for hundreds of thousands of years is changing so fast that compensatory biological responses are lagging behind, putting at risk the marine ecosystem with the highest biodiversity on Earth."
Professor Hoegh-Guldberg says the concentration of CO2 in the Earth's atmosphere is 380 parts per million (ppm), which is 80ppm higher than where it has been for the past 740,000 years, if not 20 million years. Increasing atmospheric CO2 has already brought about a +0.74°C rise in temperature, he says.
What can be done?
"If current CO2 emission trends continue, then even the most conservative estimates predict CO2 concentrations exceeding 500ppm and global temperature increases of 2°C or more by the end of the century," Professor Hoegh-Guldberg says. "Under these conditions coral reefs are likely to dwindle into insignificance; they'll be reduced to rubble, threatening the fate of those tens of millions of people whose livelihoods depend upon them.
"We clearly have to do more to reduce CO2 emissions and still more in preparing vulnerable communities to the almost inevitable problems that they will face as a result of already entrained climate change."
As world leaders gather for the last day of the United Nations Framework Convention for Climate Change (UNFCCC) meeting in Bali, the CRTR scientists argue that the issue of global CO2 emissions demands leadership at the international level, including a collective agreement on carbon emission reductions.
Says Dr Marea Hatziolos, CRTR Team Leader, World Bank, and a co-author of the Science paper: "There is an urgent need for high carbon growth countries to reduce their total CO2 emissions and a responsibility on the part of industrialized nations to assist the most vulnerable coral reef states adapt to climate change impacts while reducing local risks to reefs."
Dr Hatziolos points out that most coral reefs occur within developing countries where poverty and reliance on ecosystem goods and services place great pressure on them.
"In developing countries, tourism based on ecosystem services provided by coral reefs is a vital and rapidly expanding industry," Dr Hatziolos says. "Much of the protein consumed by poor coastal communities is supplied in one way or another by coral reefs.
"Less visible, but no less important, is the essential role played by coral reefs in providing habitat for a vast array of marine species which contribute to a complex food chain that extends across the oceans.
"The threats to this natural capital from increased CO2 emissions generated on a global scale simply raise the urgency for local reef managers and policy-makers to take responsibility for the 'reducible risk' to coral reefs, such as over-fishing, pollution and unsustainable coastal development.
"However, this is unlikely to happen, at the intensity and scale required, unless industrialised nations make funds available to assist the most vulnerable coral reef states manage these reducible risks."
Dr Hatziolos says a range of policy and management tools are readily available, some of which have been refined through support from the CRTR Program, and no time should be lost in applying them more widely and effectively.
"These tools include coastal zone management, co-management arrangements between governments and local communities to foster effective stewardship, integrated catchment approaches to managing water quality and environmental flows, enforcement and compliance with fishing regulations, restoration of reefs and coastal vegetation and sustainable tourism," she says.
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