Great Barrier Reef watchers anxiously await evidence of coral bleaching from aerial surveys.

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The aerial surveys of hundreds of reefs will be completed in the bottom two-thirds of the world’s most significant reef system, the Great Barrier Reef. Through this, the full impact of coral bleaching across the Great Barrier Reef will become clearer this week.

Last week, an aerial survey was carried out in which 500 individual reefs between the Torres Strait and Cairns showed signs of severe bleaching near the shores.

From Monday, the spotter plane will head south over reefs where satellite observations and temperature readings have shown corals are likely to have undergone higher levels of heat stress than those in the north.

Scientists fear those corals could be found to have poorly been bleached, as they are less used to higher temperatures. They had not been affected much in 2016 and 2017.

The chief scientist at the Great Barrier Reef Marine Park Authority, Dave Wachenfeld, told Guardian Australia that whatever the survey concluded, the current bleaching should sound “a deafening alarm bell” on the plight of the reef under global heating.

This summer has led to excessive heat stress building across the length of the reef where many anecdotal reports from tourism operators, tourists, and recreational diver of severe bleaching.

Scientists believe that the sea surface temperatures have been on the rise due to the accumulation of greenhouse gases by the oceans. This has mostly been a result of burning fossil fuels. Thus the temperature of the water had risen by 1.25 degrees.

Corals tend bleaching during exposure to heat. The survival of the coral depends on the fluctuations in temperature. Also, it depends on the type of coral as each of them has different susceptibility to heat.

2016 and 2017 experienced a lot of coral bleaching, and it was assumed that maybe half of the reef’s corals would be killed by this phenomenon. The central and southern parts of the beach were although not affected much in those years.

Prof Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, spent 17 hours across four days in the air last week, scoring bleaching on reefs with a staff member from the authority.

After completing the first four of nine days of aerial surveys, Hughes told Guardian Australia most of the severe bleaching had been seen at coastal reefs.

On Friday, flying from Lockhart River to Cairns, Hughes said corals at Princess Charlotte Bay at the bottom of the Cape York Peninsula had been severely bleached, but the impacts were much less on reefs further away from the coast.

Many of the outer reefs in the north – known as “ribbon reefs” because of their slim and snaking appearance from above – had escaped bleaching.