Dire warming scenarios for world’s reefs

Miguel Llanos Reporter • Profile • E-mail

They get blown up by fishermen, trampled on by tourists and suffer diseases exacerbated by warming seas. The victims here are the world's coral reefs, and if all that's not enough to do them in, there's an even bigger threat on the horizon: oceans becoming more acidic as carbon dioxide emissions increase.

"Rapid increases in the atmospheric carbon dioxide concentration, by driving global warming and ocean acidification, may be the final insult to these ecosystems," 17 scientists reported in a peer-reviewed study published in the journal Science on Friday.

Oceans soak up about a quarter of all CO2 emissions. Absorbing the CO2 reduces warming's atmospheric impact but literally changes the oceans' chemistry. That's because the absorbed CO2 produces carbonic acid — the same stuff that puts the fizz in soft drinks — and that dissolves the minerals used by corals to grow.

"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," lead author Ove Hoegh-Guldberg said in a statement issued with the study.

Video   Crumbling corals Dec. 13: Carbon dioxide emissions can cause coral destruction, a new study calculates. Peter Mumby, a University of Exeter researcher and study co-author, describes the danger using footage off Bonaire in the Caribbean and Heron Island in Australia's Great Barrier Reef. MSNBC

"These changes come at a time when reefs are already stressed by climate change, overfishing and other types of pollution," added co-author Ken Caldeira of the Carnegie Institution of Washington at Stanford University. The stress includes the practice in some waters of blasting reefs to stun and then retrieve fish for the aquarium trade.

"Unless we take action soon," Caldeira said, "there is a very real possibility that coral reefs — and everything that depends on them — will not survive this century."

Those dependents include humans. "The deterioration of coral reef ecosystems is a visually poignant reminder that climate change is not just an environmental issue but a development issue," said Katherine Sierra of the World Bank's sustainable development program. "Coral reefs are much more than a pretty picture, they’re an important asset."

Three scenarios
The researchers plotted three scenarios using the low-end of CO2 projections by the U.N. Intergovernmental Panel on Climate Change, or IPCC. Emissions are measured in parts per million of atmosphere, and the global rate is now around 380 ppm.

The projections were combined with computer simulations of how ocean chemistry changes when CO2 levels range from 280 ppm to more than 500 ppm.

In scenario A, where emissions stabilize at around 380 ppm, corals would be affected but still survive, the experts calculated.

Scenario B, where emissions continue growing at the present pace to 450-500 ppm, "reef erosion will exceed calcification," they found. "The density and diversity of corals on reefs are likely to decline, leading to vastly reduced habitat complexity and loss of biodiversity, including losses of coral associated fish and invertebrates."

Scenario C, looking at 500-600 ppm, was even more dramatic. "These changes will reduce coral reef ecosystems to crumbling frameworks," the authors wrote.

"Under these conditions, reefs will become rapidly eroding rubble banks such as those seen in some inshore regions of the Great Barrier Reef, where dense populations of corals have vanished over the past 50 to 100 years," they added. "Rapid changes in sea level, coupled with slow or nonexistent reef growth, may also lead to 'drowned' reefs in which corals and the reefs they build fail to keep up with rising sea level."

Hoegh-Guldberg, a researcher at the University of Queensland in Australia, emphasized that "under these conditions coral reefs are likely to dwindle into insignificance; they’ll be reduced to rubble."

MORE FROM CLIMATE CHANGE

Climate Change Section Front

Experts eye moving species to save them Gore pitches 10-year shift to clean energy U.S.: Warming worsens health 'disparities' Abandon ice floe, researchers told EPA unveils CO2 storage rule EPA experts list warming's health risks Bush sidesteps court ruling on warming Antarctic ice breaking up even in winter Survey: Third of coral species at risk EPA: Warming could worsen some smog Climate Change Section Front   Add Climate Change headlines to your news reader: