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Great Barrier Reef Has Worst Coral Die-Off Ever, Report Finds (usatoday.com)
Australia's Great Barrier Reef has suffered from its worst coral die-off ever recorded, according to a new study from the Australian Research Council Center of Excellence for Coral Reef Studies based at James Cook University. "Stress from the unusually warm ocean water heated by man-made climate change and the natural El Nino climate pattern caused the die-off," reports USA Today. At more than 1,400 miles long, Australia's Great Barrier Reef is the world's largest coral reef and the planet's biggest structure made by living organisms. In the northernmost section of the reef, which had been considered the most "pristine," some 67% of the coral died. The good news, scientists said, was that central and southern sections of the reef fared far better, with "only" 6% and 1% of the coral dead, respectively. Coral reefs result from the work of little polyps, creatures only a few millimeters long, budded on top of one another. Over centuries, the shells of these creatures combine to form the exotic shapes of coral reefs. Tiny differences in the anatomy of each polyp species affect the shape of their shells and produce the exotic shapes of each reef. The vibrant colors that draw thousands of tourists to the Great Barrier Reef each year come from algae that live in the corals tissue. When water temperatures become too high, coral becomes stressed and expels the algae, which leave the coral a bleached white color. Mass coral bleaching is a new phenomenon and was never observed before the 1980s as global warming ramped up. Besides their beauty, reefs shelter land from storms, and are also a habitat for myriads of species.
Disclaimer: I'm a physicist at James Cook University, where this study was published. My mother used to work at AIMS 20 years ago, my sister works for CSIRO in marine research, and my cousin-in-law is currently the Coral Reef ARC's COO.
These are results published by the Australian Research Council Centre for Coral Reef Studies. Prof. Terry Hughes, who runs this centre at JCU, has basically surrounding himself with like-minded people. The self-citation rate for articles published by the centre is remarkably high, and I quite frankly don't trust Prof. Hughes to do unbiased research, or to critically analyse his own work. There is a pretty strong monoculture of reef research, and I believe it's a pretty serious problem. One of my physics lecturers wrote a rebuttal letter to Prof Hughes that was leaked to the press, and was disciplined for it (one more strike and he's fired). I would really like to see a little more diversity in the people that study this topic.
That said, I have no reason to doubt the truth of this study. The die-off is real, and is unprecedented in modern times, and elementary physics tells us that increased temperatures due to climate change can only make it worse, not better. My mum's old boss from AIMS, Charlie Veron said in a seminar 10 years ago that the reef is probably doomed, and that even if we manage to stop all CO2 today, there's enough inertia that very little of the reef will survive.
You're partly right - the answer really varies as different reefs are affected in different ways, but fundamentally global warming can exacerbate effects such as El Nino/La Nina, so that your 3c increase may become 5c for a time. The issue is that these ecosystems are fragile and it only takes small changes to do immense damage. It's not that nature can't adapt to temperature fluctuations and such, it's that it can't adapt at the rate of change we're forcing on it. In terms of global warming in general consider the Polar Bear, normally climate would change over thousands of years and Polar Bears would become more brown, have less insular fur and move south and become more like grizzlies, but we're forcing change to their environment in decades, that's just not long enough for enough generations to be selected for brown fur - you just aren't going to go from white fur to brown fur (and possibly lose some insulating features) and adapt in that kind of compressed time frame, which is why they're at risk.
For what it's worth there are reefs that don't seem particularly affected at all by the temperature change, the Great Barrier Reef seems to be one of the most especially fragile ones, and coupled with it's immense size this makes it stand out. See my other post elsewhere on this topic where I point out that the Red Sea reefs are currently at their most vibrant they've been in a long, long time regardless of temperature change, simply because of the reduction in tourism to Egypt. In contrast, much of the Great Barrier Reef is already protected from humans, yet is still suffering. This should really highlight how different reefs are affected in different ways, that they can recover, but recovery needs different things in different reefs - lack of human presence is doing wonders in Egypt's Red Sea, but it's doing nothing for the Great Barrier Reef, my suspicion being that the Great Barrier Reef suffers far more greatly from the changes in a body as large as the Pacific than the far better protected Red Sea does where humans are by far the largest problem.
Climate change isn't an inherent problem in itself, man-made or natural, you're right, it happens. The problem is the rate of climate change that's occuring right now, that's the real issue here, nature just doesn't have sufficient time to adapt right now which is why we're seeing events like this and why this period is often being called a mass extinction event period.