Australia's Great Barrier Reef has experienced its third coral bleaching event in five years, according to researchers who blamed the rapid warming of the planet due to human emissions.
A bleaching event occurs when coral expels a type of algae that provides up to 90 per cent of their energy and gives them their colour.
This expulsion can happen when coral is under stress due to warm ocean temperatures.
Now, a new survey has found the south of the reef is bleaching extensively for the first time.
Professor Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University said: "We surveyed 1,036 reefs from the air during the last two weeks in March, to measure the extent and severity of coral bleaching throughout the Barrier Reef region.
"For the first time, severe bleaching has struck all three regions of the Great Barrier Reef - the northern, central and now large parts of the southern sectors."
Taking 11 flights over nine days in March, Professor Hughes navigated the full length of the Great Barrier Reef to survey reefs from the air.
According to aerial analysis, coastal reefs along its entire length - a stretch of about 1,500 miles (2,300 kilometers) from the northern Torres Strait to the reef's southern boundary - have been severely bleached.
In February, researchers said the area recorded its highest monthly sea surface temperatures since records began in 1900.
Professor Hughes said: "We are all in shock really at how quick this has happened. Three severe bleaching events in five years is not something we anticipated happening until the middle of the century."
Professor Morgan Pratchett, also from Coral CoE at JCU, led studies to determine how bad the recent bleaching event has been.
He said: "A pale or lightly bleached coral typically regains its colour within a few weeks or months and survives.
"We will go back underwater later this year to assess the losses of corals from this most recent event.
"The north was the worst affected region in 2016, followed by the central region in 2017. In 2020, the cumulative footprint of bleaching has expanded further to include the south."
Experts have also observed how the time frame between these bleaching events is shrinking, so the coral reef has less time to fully recover.
The bleaching event this year is not only the largest, but also the most severe on record, with much of the damage likely to be irreparable.
Professor Hughes also added that the number of reefs avoiding bleaching is dwindling each year.
He said: "As summers grow hotter and hotter, we no longer need an El Niño event to trigger mass bleaching at the scale of the Great Barrier Reef.
"Of the five events we have seen so far, only 1998 and 2016 occurred during El Niño conditions.
"We have already seen the first example of back-to-back bleaching-in the consecutive summers of 2016 and 2017."
