Proposals for geoengineering projects sound like something out of science fiction.

Pumping aerosols into the upper atmosphere to make clouds more reflective, for example. Or fertilizing oceans with iron to promote the growth of plankton and algae so they consume more carbon dioxide.

Then there are proposals to plant vast swathes of trees in desert areas, or brighten clouds above marine areas to prevent ocean warming.

They sound like drastic interventions because that's what geoengineering is: the active and intentional modification of the climate.

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As the Paris agreement target of limiting global temperature rise to two degrees or less seems increasingly improbable, there has been renewed interest in solutions that once seemed morally challenging, or difficult to contemplate.

To proponents, like Cambridge University's Hugh Hunt, geoengineering could mitigate the worst aspects of climate change, and provide time to look for more permanent solutions.

"It's a little bit like someone with lung cancer - we're not going to give you a transplant if you're going to carry on smoking," he said.

"Geoengineering will buy us some time, until we get this sorted out."

Dare not speak its name

Dr Hunt is currently investigating the construction of huge updraft towers in the desert, and using the air flows to generate electricity while stripping the airstream of greenhouse gasses.

He previously worked on a project named SPICE — Stratospheric Particle Injection for Climate Engineering — which looked at sending a tethered balloon 20km above to earth to seed aerosols into the stratosphere.

In theory, the particles would change the optical properties of sunlight, reflecting more solar radiation into space and reducing global temperatures.

The idea was to emulate natural volcanic events, like the 1991 eruption of Mount Pinatubo in the Philippines, which caused global cooling of one degree for about a year.

The Great Barrier Reef has struggled with two consecutive years of serious bleaching. ( Supplied: Caitlin Seaview Survey 2015 )

Intellectual property concerns were among the reasons SPICE and its balloon fell back to earth, figuratively speaking.

"It was closed down because it was deemed to be controversial," he said.

Dr Hunt is concerned about the lack of research into geoengineering solutions, which he says could leave the international community seriously unprepared if any country decided to act unilaterally.

"If they could be made to work, they could be quite cheap - the development time can be short, and the cost low," he said.

"It's like the Voldemort of climate change - it shall not be mentioned.

"My view is if something is going to be done, best we know how to do it safely. I think we should be allowing experiments, but I'm in a very small minority.

Adaptation on the Great Barrier Reef

They may seem far fetched, but geoengineering projects have already been proposed for areas in Australia's backyard.

One of the markers of global climate change is the health of the world's coral reefs, which are particularly sensitive to changing temperatures.

Following two consecutive years of mass coral bleaching, a team of researchers at the Sydney Institute of Marine Science last year proposed altering the clouds above the reef in a bid to save the delicate coral communities below.

They advocated "marine cloud brightening", making larger and more reflective clouds over the ocean to cool the water underneath.

Great Barrier Reef Marine Park Authority (GBRMPA) chief scientist David Wachenfeld said the authority has already undertaken local action to improve the resilience of the reef to climate change, which he said was "far and away the greatest threat" to its survival.

Although they are much smaller in scope than those proposed by geoengineering advocates like Dr Hunt, Dr Wachenfeld said the GBRMPA had already looked at adaptation and marine park management to reduce human impact on the reef, include altering turtle nesting habitats to ensure greater numbers survive each year.

"These areas can certainly still recover if we do the right thing in terms of global mitigation of climate change and local actions to improve resilience," he said.

"We need to try harder, do more and act now."

'What happens if we screw it all up?'

Summer ice in the Arctic is now so thin that researchers last year sailed in small yachts rather than large ice breaking ships.

Scientists say as much as 50 gigatons of methane trapped under the Arctic could be released into the atmosphere if — or when — the protective permafrost completely melts, rapidly speeding up global climate change.

Ice is disappearing from the Arctic. ( Kathryn Hansen/NASA )

The upshot of this and other climatic developments, according to Dr Hunt, is the need to urgently look at solutions that would otherwise seem unthinkable.

But he is not closed to the very real risk of catastrophe that geoengineering poses, pointing out that there are "hundreds" of potential adverse impacts. Most importantly, there is no "Planet B" if we get it wrong.

"The obvious ones are pumping something up high into the atmosphere and we know so little about the upper atmosphere - whatever we put up there has got to be safe," he said.

"What happens if we screw it all up? What happens if we accidentally switch off the Indian monsoon?"

Besides this, there is the risk the projects do not work at all, or are not as effective as advertised.

But Dr Hunt said this required more research and thought applied to the topic.

"I don't know which is worse - a seven metre sea level rise or geoengineering.

"That's putting it in a very pointed way, but we've got to think hard about this.

"It could be that there should be absolutely no way we ever do this. But that's why we've got to do the research."

Dr Hunt and Dr Wachenfeld spoke at the Climate Adaptation 2018 conference in Melbourne, recorded and broadcast by RN's Big Ideas.