Ocean temperatures over parts of the Great Barrier Reef have reached record highs this month, raising fears of a second consecutive summer of massive coral bleaching.
Data from the US government’s National Oceanic and Atmospheric Administration (NOAA) shows sea surface temperatures in the northern parts of the reef were the highest in any November since a record high dating back to 1985.
With the peak period of accumulated heat on the reef not expected until February, cooler weather and cyclonic activity before then could prevent a massive bleaching event.
Professor Terry Hughes, a leading expert on coral bleaching at James Cook University, said he had never seen heat stress build up on the reef so early, but a “cyclone at the right moment” in December could reduce the risk of money laundering.
“It is certain that the temperature records are collapsing. The warning signs are clear,” he said.
Last summer’s massive bleaching, declared by the Great BarrierReef Marine Park Authority (GBRMPA), was the first outbreak of La Niña – a climate pattern that has historically kept ocean temperatures cool enough to avoid bleaching.
Hughes said: “Based on Noaa’s predictions, there’s a good chance we’ll see another back-to-back bleaching event. This was not supposed to happen until the middle of this century.
Rising ocean temperatures due to human emissions of greenhouse gases primarily from burning fossil fuels caused six episodes of massive bleaching along the reef in 1998, 2002, 2016, 2017, 2020 and 2022.
Last summer’s bleaching that affected 91% of all individual reefs came after record high ocean temperatures on the reef in December.
But according to data from Noaa, there is currently more heat accumulated on the reef to the north than at the same time last year.
A current forecast from Noaa suggests that by the end of January large parts of the northern reef are likely to experience significant bleaching, and in the weeks ahead some areas could experience enough heat to cause coral death.
The Bureau of Meteorology forecasts for sea surface temperatures also show that heat builds up in December and January on the reef.
Observations show current temperatures in the central and northern parts of the reef at around 2°C above average.
Corals can recover from bleaching if temperatures are not severe. Scientists have seen an increase in the amount of coral on the reef in recent years – a recovery driven by fast-growing corals which experts say are also the most susceptible to bleaching.
GBRMPA chief scientist Dr David Wachenfeld said the authority was reviewing Noaa and the bureau’s forecast “to understand what might happen this summer”.
He said conditions leading into this summer were of concern, but said ‘local weather patterns will strongly influence sea surface temperatures throughout the summer – for example, if it rains or there are cloudy conditions. Temperatures also tend to be warmest in February.
“At this time it is too early to tell what this summer will mean for the reef, although the current La Niña event is expected to increase rainfall along the east and northeast coast.”
He said the authority would use satellite, aerial and underwater observations to monitor conditions and make forecasts.
Professor Ove Hoegh-Guldberg, a pioneering coral bleaching scientist at the University of Queensland, said: ‘It’s about the steady but rapid rise in ocean temperatures and it’s very worrying. This [heat stress] happens several weeks earlier than usual – in the past it was in January. I had to check my watch.
“The fact that it’s probably the hottest November on record [over the reef] and given what we know about heat stress on corals, that doesn’t bode well.
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