The impact of climate change on the Great Barrier Reef
The corals of the reef have been bleached white for a second year in a row
The Economist explains
May 5th 2017by R.M. | SYDNEY
THE Great Barrier Reef stretches some 2,300 km down Australia’s north-east coast, covering an area the size of Italy. It is home to about 600 types of coral and 1,625 species of fish. UNESCO calls it a “site of remarkable variety and beauty”.
That may not last. For the second consecutive year, expanses of coral have lost the vivid colours that draw thousands of annual sightseers. Instead, they have bleached a deathly white. Worse, this year the bleaching has extended further south than in 2016. Bleachings were also reported in 1998 and 2002. But for it to happen two years running is unprecedented. Why are the corals turning white?
One factor is the nutrients and pesticides flowing into the ocean from coastal farms and cities in the north-eastern state of Queensland, which have polluted its waters.
But experts agree that the biggest culprit is warmer ocean temperatures linked to climate change.
Corals are marine animals that get their colour and most of their food from the algae that live within them. The higher temperatures stress algae, causing the rich hues to disappear. Some marine scientists liken this to the impact of a prolonged heatwave or drought on a forest. The Climate Council, an Australian research body, says the reef’s surface sea temperatures in early 2016 were the hottest since records began in 1900.
Under prolonged stress corals can expel algae, causing them to starve and die.
In the northern region, where bleaching was most intense, the coral mortality figure was alarming: about two-thirds. Depending on different coral species’ capacity to resist stress, and the distribution of heat patterns through waters, reefs can revive over several years. The difference this time, say experts, is that back-to-back bleaching from two successive seasons of extreme heat have given the reef no time to recover, and have lowered its corals’ stress tolerance. It is too early to measure coral deaths from the 2017 bleaching, but the Climate Council predicts “high mortality rates”.
Two years ago UNESCO was concerned enough about the reef’s health to consider adding it to the short list of world heritage sites in danger.
The Australian and Queensland state governments responded with a plan aimed at improving the local marine environment.
Yet both governments simultaneously support a plan by Adani, an Indian energy company, to open one of Australia’s biggest coal mines in the Queensland outback, and to ship coal to India from Abbot Point, on the Queensland coast, through the reef’s waters.
Russell Reichelt, head of the Great Barrier Reef Marine Park Authority, says there are signs that such happenings will become more frequent due to rising ocean temperatures: “If they do, it will change the whole character of the coral community.”
The reef looks set to become Australia’s next environmental battleground.
Press link for more: The Economist