James Cook University professor Terry Hughes says he flew over 600km of reef and more than 60% was bleached

This article is more than 4 years old

This article is more than 4 years old

An aerial survey is revealing the worst bleaching ever seen on northern parts of the Great Barrier Reef, as the scientist leading the survey live-tweets the devastation and pleads for the world to take action on climate change.

Last week Terry Hughes, a professor at James Cook University and convener of the National Coral Bleaching Taskforce, told Guardian Australia he planned to hire a charter plane and map the bleaching to see how bad it was.

They would start from Cairns and fly north, he said. “We’ll expand that initial aerial survey to crisscross the whole northern region and map it all out.”

Now, using both planes and helicopters, Hughes has found what he says is the worst bleaching in the region he has ever seen.

On Tuesday, Hughes said he surveyed 600km of reef and found that more than 60% of it had been bleached.

Terry Hughes (@ProfTerryHughes) Day 1 of #coral #bleaching surveys on #GreatBarrierReef. 179 reefs surveyed along 600km track, most >60% bleached pic.twitter.com/o5e4KgsU6W

That was just two days after the Great Barrier Reef Marine Park Authority raised the threat level of coral bleaching to the highest possible alert, “level 3” , indicating “severe regional bleaching” in the northernmost quarter of the 344,400 sq km marine park.

On Wednesday Hughes upgraded to a helicopter and continued the survey.

Terry Hughes (@ProfTerryHughes) Day 2, flew 1200km in 8 hours. We stopped for lunch here. pic.twitter.com/X8XNNk78dz

Over the following days, Hughes tweeted photographs of reef after reef, all appearing stark white.

On day three, he said only four of 400 reefs he saw were not bleached and that, while there had been bleaching in 1998 and 2002, this event was the worst.

Terry Hughes (@ProfTerryHughes) Day 3: 400 reefs scored by lunchtime. FOUR of them have no #bleaching. pic.twitter.com/8NWGaK3GFQ

Bleaching occurs when coral gets stressed, usually by heat, and it expels the colourful algae that live inside it, giving it its brilliant colour and providing it with most of the energy it needs. If it stays bleached for long enough, the corals die and the reefs risk being colonised by other organisms such as seaweed.

This bleaching event is linked to the current El Niño, which raises temperatures in the region, on top of climate change-induced warming.

While Hughes surveyed the reefs from the air, other teams were in ships, examining the coral up close to get a more in-depth picture of which corals were bleaching, he said.

Terry Hughes (@ProfTerryHughes) Day 2 #coral bleaching surveys. 322 reefs assessed now. Most look like this. Ban #coal mines. pic.twitter.com/Jm9raFppwT

Terry Hughes (@ProfTerryHughes) Day 3: Even in the remote Torres Strait, #coral #bleaching is extreme. VOTE for the Reef, not for #coal pic.twitter.com/QtxHueSApn