Mass coral bleaching events are among the most conspicuous signs of the extent to which our oceans are warming.
The latest alarming evidence indicates that reefs themselves can heat up substantially more than the waters surrounding them, adding to the shock the coral experiences from considerable temperature changes.
It is this heat change that stresses the corals, causing bleaching that can kill living reefs.
A recent study, led by Thomas DeCarlo at the University of Western Australia, demonstrates that much of the world’s coral is more vulnerable than previously thought.
During June 2015, the South China Sea warmed up by 2C as is usual following an El Nino weather pattern.
The temporary rise in temperature was not expected to have a serious impact on coral.
However in some northerly parts of the sea, the temperature rises were steeper. At Dongesha Atoll, sea-surface temperatures rose as much as 6C above average, which killed 40 per cent of the coral.
According to researchers, the shallow water amplified the El Nino effect, while unusually weak winds meant heat was trapped in the area for an unusually long period.
Speaking to the New Scientist, Mr DeCarlo said: “Ocean temperatures are already warming due to climate change.”
“But what we’ve shown is that on top of that, local weather anomalies or processes like reduced wind can drive reef temperatures even higher. That compounds the risk that corals are facing.”
The evidence from the study adds greater weight to arguments that current targets for reducing damaging greenhouse gas emissions are not enough to prevent catastrophic loss of the world’s coral reefs.
Sea surface temperatures around the planet have risen by an average of 0.07C each decade over the last century.
Under the terms of the Paris climate change agreement, signature countries are obliged to work towards limiting global climate change to a rise of 2C, but this may not be enough to prevent catastrophic loss of coral.
In January Japan’s environment ministry reported that over 70 per cent of the country’s largest coral reef was “dead” after sea temperatures were between one and two degrees Celsius higher than normal.
In Australia, a heatwave which caused record-breaking temperatures and wildfires earlier this year has also meant no relief for the Great Barrier Reef, which was ravaged by heat-induced bleaching last year, killing swathes of the coral.
In February Dr Gareth Williams of Bangor University told The Independent that though the situation was “terrifying” immediate action could save coral reefs.
He said: “The critical thing here is that we have to tackle global climate change. But what will save coral reefs is a planet-wide multi-government co-ordinated effort to reduce greenhouse gas emissions.
“There’s huge danger in thinking we can climate-proof coral reefs. That’s a dangerous idea. We have to start tackling the root cause of this, and the root cause is global climate change.”Reuse content