Scientists say they are planning to scale up an experiment using cloud-brightening technology to slow the impact of coral bleaching on the Great Barrier Reef.

Key points: Droplets of salt water shot from a snow cannon mix with clouds to brighten them

Droplets of salt water shot from a snow cannon mix with clouds to brighten them The brighter clouds can reflect the sun and reduce heat on the reef

The brighter clouds can reflect the sun and reduce heat on the reef It is considered a way to protect the reef from coral bleaching

The technique uses a device like a snow cannon to shoot microscopic saltwater droplets into the air.

In theory, the smaller droplets mix with low-altitude clouds which brighten enough to reflect the sun and reduce heat on the reef.

It is considered one way to protect the reef from mass coral bleaching as it experiences its third event in five years.

"The corals were bleaching all around us while we conducted our tests," project leader Daniel Harrison said.

"This was both shocking and heartbreaking in what should have been an ordinary non-El Nino, non-bleaching year.

"It really emphasises how little time we have for this research."

The technique uses a device to shoot salt water into clouds. ( Supplied: Brendan Kelaher/SCU )

While COVID-19 restrictions prevented international researchers from joining the trial, a local contingent set off last month in two large vessels to Broadhurst Reef, 100 kilometres off the coast of Townsville.

To remain isolated from coronavirus, the team drove the 3,600-kilometre return trip from Coffs Harbour to Townsville, camping and cooking along the way.

They carried a prototype cloud-brightening machine, air-sampling equipment and 80 kilograms of instrumentation.

Dr Harrison, from Southern Cross University and the Sydney Institute of Marine Science, said while the brightening machine worked, more trials were needed over the next four years to prove the theory.

"The technology worked a lot better than we planned at these early stages," he said.

"With the drone we could see, as we hoped, the [salt crystals] are getting mixed up into the atmospheric boundary layer towards the clouds.

The prototype was tested near Broadhurst Reef off Townsville. ( Supplied: Brendan Kelaher/SCU )

"We're aiming in about four years' time to have a couple of stations that are large enough to do a big experiment where we will actually try to brighten the clouds and look at how well it works.

"One machine, or the three, will be able to do cloud brightening over around a 400-square-kilometre area."

'We were amazed'

Dr Harrison formed his hypothesis for the technique during a previous research project in 2017.

Knowing that every cloud droplet needed a nucleus to condense onto, he theorised there might be a shortage of suitable nuclei during summer when coral bleaching occurred.

"Nobody had previously measured atmospheric particle concentrations above the reef before and during bleaching events," Dr Harrison said.

"We were amazed to see that the number of atmospheric nuclei were far lower than even I expected."

Using the cloud-brightening machine, the team was able to create hundreds of trillions of sea salt crystals per second which floated into the sky to bolster the existing clouds' reflectivity.

Daniel Harrison is leading the cloud-brightening trials. ( Supplied: Southern Cross University )

Further trials for the cloud-brightening approach, along with 42 other concepts, will be funded by the Federal Government's $150 million reef restoration and adaptation package, announced this week.

"We don't know yet which interventions are going to prove to be winners," Dr Harrison said.

"The risks to the environment potentially are that there could be some minor changes in rainfall patterns over the reef and we need to do research into that area."

He said the technology was relatively cheap.

"It's about $150 million to $200 million a year to run cloud brightening over the whole reef; it's fairly small in comparison to the $7 billion or so a year that the reef brings into the Australian economy.

"It's actually protecting the reef as it already is … trying to restore it is a much harder and, I think, ultimately more expensive proposition, because once it's gone, it's a lot harder to replace it.

"With cloud brightening, you only need to put in a very small amount of energy to potentially get a large amount of cooling because nature is doing all the work for you."

But he said ultimately, more work was needed to reduce emissions.

"That's the only thing that's going to ultimately save the future of the Great Barrier Reef," Dr Harrison said.

Cloud brightening involves spraying microscopic seawater droplets into the air. ( Supplied: Alejandro Tagliafico/SIMS/SCU )

A lifeline for the reef

Mundaburra man Usop Drahm was a part of the team aboard the research vessels and said the traditional owners of the area welcomed the project.

"The reef has always provided food for us and it is a part of Mother Earth, which in turn is a part of us," he said.

"With the reef dying and the temperatures being quite high, anything that can help with that, that doesn't have an impact in another way, is good.

"If you are picking up seawater from the ocean and spraying it across the ocean, you are not taking anything away, and you are not adding anything to the water, so that is all a positive."