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White out Ethan Daniels
28 Nov
Since 2014, a global bleaching event has threatened corals. This season’s El Niño could make it worse

According to the US National Oceanographic and Atmospheric Administration (NOAA), next year’s El Niño is predicted to be one of the strongest since records began. The temperature rise is likely to spread a global bleaching event already taking place in the Pacific and Indian Oceans, NOAA scientists say.

Dr Mark Eakin, NOAA’s coral reef watch coordinator, says ‘the current bleaching event started in mid-2014 and has been causing bleaching in the Pacific Ocean since then. This spread to the Indian Ocean and Atlantic and Caribbean this year. Next year, the impact in the Indian Ocean and Atlantic Caribbean will likely reoccur and may be even worse’.

Bleaching occurs when living algae evacuates the coral structure, causing it to lose colour and one half of its symbiotic relationship. Left under stressful conditions for too long, the algae does not return and the corals can die. Scientists say that local high temperatures have already put some reefs, such as those in Hawaii, under stress.

While El Niño is not triggered by climate change, it is thought to exacerbate its impacts. ‘El Niño results in unusually hot surface water temperatures,’ says Dr Jörg Wiedenmann, Head of the Coral Reef Lab at the National Oceanography Centre in Southampton. ‘There is a danger that large El Niños add to the damage done by other heat stress episodes in non-El Niño years.’

Wiedenmann believes it is mostly the intensity and frequency of episodes of overheated waters that cause bleaching, as opposed to the steady increase in average temperatures caused by global warming.

‘What really has us concerned is that this event has been going on for more than a year,’ says Eakin, ‘and our preliminary model projections indicate it’s likely to last well into next year.’

Other indicators provide further evidence of the strength of the imminent El Niño. Last week, the NOAA announced that temperatures in the ‘Nino 3.4’ region, a central band of ocean running either side of the equator from 5S-5N and 170-120W, were 3ºC above average, the highest ever such recorded temperature. Prior to the infamously destructive 1997-98 El Niño, this measurement reached a recorded high of only 2.8ºC.

Furthermore, a recent University of Brighton study found a strong correlation between historical El Niño events and droughts in southern Africa. ‘Results indicate that the region was affected by severe or multi-year drought on eight occasions,’ says lead author David Nash, from the University of Brighton’’s College of Life, Health and Physical Sciences. ‘Given that this year’s Pacific El Niño event is likely to be the strongest ever recorded, these are potentially worrying times for the people of the subcontinent.”’

This article was published in the December 2015 edition of Geographical magazine.

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