Will 90% of reefs disappear even if we curb greenhouse gases? Some recent studies suggest this will be so. And some recent comments by scientists suggest this view is too pessimistic.
According to a study by Long Cao and Ken Caldeira, any climate change action will come too late to save most of the world's coral reefs. Human activity over the last two centuries has produced enough acid to lower the average pH of global ocean surface waters by about 0.1 units, placing more than 90% of coral reefs in jeopardy. "We can't say for sure that [the reefs] will disappear but ... the likelihood they will be able to persist is pretty small." Here's another article about the study.
Another study led by Ove Hoegh-Guldberg suggests that rising carbon dioxide levels in the world's oceans due to climate change, combined with rising sea temperatures, could accelerate coral bleaching, destroying some reefs before 2050. "Previous predictions of coral bleaching have been far too conservative, because they didn't factor in the effect of acidification on the bleaching process and how the two interact." Some coral species were able to cope with higher levels of ocean acidification by enhancing their rates of photosynthesis, but if CO2 levels became too high "the coral-algal system crashes and the corals die."
In an earlier study Ove Hoegh-Guldberg also found that sea water covering 98 percent of all coral reefs may be too acidic by 2050 for some corals to live, and while others may survive they would be unable to build reefs. Unless still rising carbon dioxide emissions fall in the near future, existing reefs could all be dying by 2100.
Some scientists have commented on Ove Hoegh-Guldberg's study and suggest that "Ove is very dismissive of coral's ability to adapt, to respond in an evolutionary manner to climate change. Coral has an underappreciated capacity to evolve. It's one of the biological laws that, wherever you look, organisms have adapted to radical changes."
"There will be sweeping changes in the relative abundance of species. There'll be changes in what species occur where. But wholesale destruction of reefs? I think that's overly pessimistic."
The Coral Reef Alliance (CORAL) at at the recent International Coral Reef Symposium "agreed that the demise of coral reefs is not a foregone conclusion. Though time is running out, building resilience through large networks of marine protected areas will be key in securing the future of coral reefs."
"Cao and Caldeira have written the post mortem while the patient is still alive. There are currently a large number of conservation projects worldwide that get to the heart of building resilience to climate impacts—and many are already showing positive results."