australia's great barrier reef is one of the world's greatest reservoirs of biodiversity.  a world heritage site, it is currently under assault from unusually hot ocean temperatures, which is causing widespread coral bleaching that is damaging and, in some cases, even killing the reefs.  now a new study by scientists at the australian research council finds that the ongoing bleaching event is mainly due to human-caused global warming, and that if global warming proceeds as currently expected, "large parts" of the great barrier reef could die by the mid-2030s.  the study has not yet been submitted for peer review in a scientific journal. and until this study is reviewed and published in a scientific journal, its results should be treated as preliminary, but consistent with other recent climate science research.  the study examines what has caused ocean temperatures to spike to record highs in the coral sea region, which encompasses much of the great barrier reef, including the hardest-hit northern reaches.    "this area has recorded a big increase in temperatures over the past century, with march 2016 being the warmest on record," the researchers wrote in a piece published at the conversation on thursday, a website that publishes academic works.  coral bleaching occurs when coral expels the algae that lives in its tissue, giving it color and nutrients. this action, caused by stresses such as increased water temperature and pollution, leaves the coral skeleton exposed, making it more susceptible to heat stress, disease and pollution.  sea surface temperatures in march 2016. image: mitchell black    the analysis used methods that have also been used to analyze other extreme weather and climate events, including record heat waves and extreme precipitation events.  the scientists found that human-caused global warming made the record warm ocean temperatures and related bleaching events seen this year at least 175 times more likely to occur. the analysis found that climate change increased ocean temperatures by 1 degree celsius, or 1.8 degrees fahrenheit, during march.  coral bleaching on the great barrier reef in 2016. image: catlin seaview survey  the study projects that this year's extreme warmth is likely to occur every two years in the month of march by the year 2034.  the analysis' findings dovetail with other research that has predicted the mass die-off of coral reefs around the planet by the year 2050, as waters warm and exceed the tolerance level of many coral reef systems.  “we have loaded the odds against the survival of one of the world’s greatest natural wonders”  “these extreme temperatures will become commonplace by the 2030s putting a great strain on the ecosystems of the great barrier reef,” said lead author andrew king of the arc centre of excellence for climate system science, in a statement.  “we have loaded the odds against the survival of one of the world’s greatest natural wonders,” he said.  although the study has yet to be peer-reviewed, the methods used to detect the role of climate change in extreme events are becoming more firmly established in the climate science community.  "we hope to submit a more comprehensive version of this analysis for peer-review soon," king told mashable in an interview.  such extreme event attribution studies have been used to detect the influence of human-caused global warming in other extreme temperature events.  for this study, researchers looked at temperature data and computer model simulations that included only natural factors that alter the climate, compared to simulations that include human emissions of greenhouse gases.  they found that the simulations that include greenhouse gases best fit the temperature data, and using statistical techniques they calculated the amount of the ocean warming that should be attributed to human-caused global warming, something known as "fractional attributable risk."  in a blog post, the researchers said that they released the results prior to peer review "because of the grave nature of their findings and importance of the great barrier reef to all australians."  “we are confident in the results because these kind of attribution studies are well established, but what we found demands urgent action if we are to preserve the reef,” king said.  “for this reason, we felt it was vital to get our findings out as quickly as possible.”  coral reefs as the tripwire for "dangerous interference" with climate  the new analysis adds more evidence for those who argue that global warming may already be causing "dangerous interference with the climate system."  that vague phrase from a 1992 u.n. climate treaty established what the nations of the world should work to avoid by cutting emissions of greenhouse gases, such as carbon dioxide and methane.  temperature projection showing that march 2016 temperatures become typical by 2034. image: geert jan van oldenborgh/knmi in the netherlands.  the paris agreement on climate change, which 172 countries signed on april 22, maintains that goal as its ultimate objective, without defining it.  this new analysis suggests we have already crossed into "dangerous" territory.  "the damage to the reef is a very clear indicator of the harm our greenhouse gas emissions are doing to the planet," king said.  "hopefully this severe bleaching will help to trigger action so that we can curb our emissions."    a before and after image of the bleaching in american samoa. the first image was taken in december 2014. the second image was taken in february 2015. image: catlin seaview survey  a strong el niño climate event, combined with the impact of global warming and other factors, has prompted unusually warm ocean temperatures and the world's third-ever global coral bleaching event, which began in 2014 and is expected to continue until 2017.  the bleaching seen in the coral sea is part of this event.    heidi cullen, the chief scientist for climate central in new jersey who leads a consortium of researchers who conduct extreme event attribution studies, told mashable that this new analysis "makes clear the heavy toll of burning fossil fuels."  "it is the ultimate alarm bell that we need to drastically reduce our greenhouse gas emissions right away," she said.  cullen was not involved in the new study.  the projection that much of the great barrier reef could perish within the next few decades could turn out to be too pessimistic, since other research has shown that some species of corals are surprisingly resilient to the stress from changing ocean temperatures.                          in a press release on march 29, the australian coral bleaching task force announced that the northern portions of the great barrier reef are in the throes of the most intense coral bleaching event on record there.  the task force, comprised of 10 australian research institutions, made its determination after completing aerial surveys of more than 500 coral reefs from cairns north to papua new guinea.  “this has been the saddest research trip of my life,” says prof. terry hughes, convener of the national coral bleaching taskforce, said in a press release.  “almost without exception, every reef we flew across showed consistently high levels of bleaching, from the reef slope right up onto the top of the reef," hughes said.  "we flew for 4,000 kilometers in the most pristine parts of the great barrier reef, and saw only four reefs that had no bleaching. the severity is much greater than in earlier bleaching events in 2002 or 1998.”  the ongoing global bleaching event is the longest-lasting one ever observed, and only the third ever seen. it has occurred during the warmest year on record, which occurred in 2015, and the two most unusually mild months on earth, which took place in january and february, respectively.  “this has been the saddest research trip of my life”  it is due to record warm ocean temperatures around the world, partly driven by a strong el niño event in the tropical pacific ocean.
great barrier reef may perish by 2030s as ocean temperatures skyrocket, study finds