Coral Reefs Will Suffer If Climate Change Goes Unchecked
September 17, 2012

Coral Reefs Will Suffer If Climate Change Goes Unchecked

Brett Smith for - Your Universe Online

Time may be running out for the world´s coral reefs which could be severely victimized by rising global temperatures and carbon dioxide levels, according to a new report in Nature Climate Change.

"Our findings show that under current assumptions regarding thermal sensitivity, coral reefs might no longer be prominent coastal ecosystems if global mean temperatures actually exceed 2 degrees Celsius (3.6 Fahrenheit) above the pre-industrial level," said study author Katja Frieler from the Potsdam Institute for Climate Impact Research.

"Without a yet uncertain process of adaptation or acclimation, however, already about 70% of corals are projected to suffer from long-term degradation by 2030 even under an ambitious mitigation scenario."

Because corals depend on a symbiosis with a certain type of microalgae, they are sensitive to small increases in water temperature. The death of these symbiotic algae causes the coral reefs to "bleach" or turn pale and could lead to massive reef die-off if the warmer temperatures continue.

"This happened in 1998, when an estimated 16% of corals were lost in a single, prolonged period of warmth worldwide," Frieler said.

An international team of researchers used 19 different climate models based on carbon emissions and average global temperatures to calculate the future sustainability of over 2,100 reefs in the most comprehensive study on reef bleaching to date. Their models represent over 32,000 simulation years and a fairly robust analysis compared to previous studies.

Some biologists have put forward mitigation strategies and scenarios that could prevent a massive bleaching of these reefs, such as the emergence of symbiotic algae with a higher thermal tolerance. The researchers point out that those possible developments, which they accounted for in their study, would still not prevent some level of reef damage at this point.

"Corals themselves have all the wrong characteristics to be able to rapidly evolve new thermal tolerances," said co-author Ove Hoegh-Guldberg, a marine biologist at the University of Queensland in Australia. "They have long lifecycles of 5-100 years and they show low levels of diversity due to the fact that corals can reproduce by cloning themselves. They are not like fruit flies which can evolve much faster."

In addition to the threat of rising global temperatures, coral reefs could also face the hazard of ocean acidification. As more and more carbon dioxide enters the atmosphere, the ocean absorbs greater amounts, resulting in more acidic seawater. Higher acidity hampers the calcification process coral use to protect themselves and could affect their durability in general.

Based on the potential impact of further acidification, Hoegh-Guldberg said, “the current assumptions on thermal sensitivity might underestimate, not overestimate, the future impact of climate change on corals."

Overall, the study provides further evidence of the dangers of increased levels of carbon dioxide in the atmosphere and suggests that we may already passed the point of complete prevention.

"The window of opportunity to preserve the majority of coral reefs, part of the world's natural heritage, is small," said co-author Malte Meinshausen, a professor at the University of Melbourne. "We close this window, if we follow another decade of ballooning global greenhouse-gas emissions."