Despite the past three sodden La Niña years on the East Coast, Australians are unlikely to forget the Millennium Drought.
The twelve-year long drought carved an indelible scar on the landscape of southern Australia, devastating farmers in particular. Victoria was the first state hit, but the drought eventually dug its fingers into most of Australia bar the Northern Territory. Melbourne’s water storages dropped from 97.5% in October 1996 to just 33% by June of 2010.
The Millennium Drought was the first major Australian drought to be partly attributed to anthropogenic global warming, though it was also driven by a prolonged period of El Niño over the Pacific Ocean.
Australia faced another trying drought between 2017 to 2019, which contributed to the devastating 2019-20 bushfires.
Current climate models predict more severe droughts in the future as the world warms. Could cloud-seeding save us from another millennium drought?
In the western US, policymakers are hoping so. A February 2022 study in Nature Climate Change found that the period between 2000 and 2021 was the driest 22 years in the US mid-west in more than a millennium. That study attributed a fifth of the drought to anthropogenic climate change.
To respond to the mega crisis, several Western US states have resorted to cloud seeding in a desperate attempt to bulk up precipitation. Those states include Idaho, Utah, Colorado, Wyoming and California.
“The last 10 years of drought have led to an acceleration of these programmes and advances in the science, and the drought has certainly caused a much greater interest in glaciogenic seeding in the western US,” says Steven Siems, an expert in cloud microphysics and precipitation at Monash University.
Siems is also a member of the World Meteorological Organisation’s expert team for weather modification, a group that promotes research into weather modification practices. He’s worked with both Hydro Tasmania and Snowy Hydro, and he was on the science oversight panel for the 2008 Queensland cloud seeding research program.
But while western US cloud-seeding activities have had some limited success in enhancing snowfall – thus increasing the availability of water in the warmer months – these activities have barely scratched the surface of the region’s drought problem.
Siems says part of the reason is that you need incredibly specific conditions, including very specific cloud types, to actually be able to seed.
“First off, cloud seeding is very limited,” he says. “Here in Australia you’re looking at Tasmania and the Snowy Mountains, and Victoria could do it if it wanted to in the winter time. But you’re not looking at busting a drought in the middle of the summer, that doesn’t work.”
For the silver iodide particles to find water particles to cling to, you need super-cooled liquid water droplets that remain liquid even when temperatures drop below freezing. That only happens in specific types of clouds, most of which form during the winter. That’s also why the 2008 Queensland program failed.
“So, I don’t think that’s going to be a silver bullet for us,” Siems says.
Cloud-brighteners: weather modification may shield the Great Barrier Reef
There’s another way in which scientists are trying to modify the weather to solve an Australian problem, and this method is showing some promise.
In 2020, a team of researchers led by Dr Daniel Harrison of Southern Cross University, loaded up a repurposed ferry with what looked like a large, white cannon, took it out to a vulnerable part of the Great Barrier Reef, and began spraying seawater into the sky.
The Reef Restoration and Adaptation Program, the largest concerted scientific effort to save the reef from the devastating impact of climate change, is looking to insulate vulnerable parts of the reef from bleaching events. It’s doing this by intervening in an unprecedented way: changing the composition of the clouds that drift over the natural wonder.
Enter the massive cannon shooting salt water off the back of a former car ferry.
The salt particles in the water that are sprayed over the reef travel upwards into the clouds as the water evaporates, forming nuclei around which vapour can condense, thickening the clouds and so making them brighter – meaning they reflect more light away from the vulnerable reef below.
“We as humans are doing cloud brightening all the time accidentally, because we’re releasing lots of extra aerosols into the air, some of which are good cloud condensation nuclei,” says Harrison. “So, we’re inadvertently brightening clouds on a global scale.”
Marine cloud brightening is being posited as a genuine adaptation technique to deal with anthropogenic global heating, under the international Marine Cloud Brightening (MCB) Project, headed up by Professor Robert Wood, an atmospheric scientist at the University of Washington.
The principle is basically provable – more particles in the atmosphere equals less heat. In 1991, Mount Pinatubo in the Philippines erupted, spewing an estimated 20 million tonnes of sulphur dioxide particles into the atmosphere. Those particles cooled the planet by around 0.5C – as reported in Nature, for about 18 months average global temperatures returned to what they had been before the arrival of the steam engine.
The Great Barrier Reef program, by contrast, has a more modest goal: to protect vulnerable reefs at the hottest times of year, on a case-by-case basis, almost like putting out spot-fires. It’s also one of the very first of its kind.
“For thirty years people have researched cloud brightening, but its always been entirely theoretical, and there’s been very few people who have actually tried to look at how you could do this in the real world,” says Harrison.
“The real challenge is producing the absolutely immense numbers of cloud condensation nuclei from seawater, atomising the seawater at a sufficient rate for a reasonable amount of energy,” he says.
At this stage, the project is still ironing out the finer details, like the correct nozzle size for atomising the water. They’re also still gathering the data, which is not yet comprehensive enough to prove their concept – though Harrison believes it’s getting there.
“We’re still at an early stage, where we’re trying to understand, what are the key parameters? How do you make more efficient machines? How much energy will they require? What type of droplets are produced?”
That last point is important because, as Harrison points out, the wrong type of droplet could be a disaster: “different sized droplets affect the cloud in different ways – so if you make the wrong sized droplets you can actually make the cloud dimmer instead of brighter.”
As well as proving the concept and demonstrating its effectiveness, the program estimates deployment of cloud brightening as a firefighting tool to protect parts of the reef is still at least a decade off because of the regulatory and social license work that needs to be done.
But if it works, this program could form the model for similar practises globally, as we move into the adaptive phase of our encounters with climate change.
According to Harrison, these kinds of nimble, adaptable approaches will be critical for protecting the reef. Traditional conservation work simply won’t cut it.
“The reef is the size of Italy, something like 90 per cent of the reef, no one ever goes there,” he says. “It’s just so large, and so remote, that more traditional conservation techniques just can’t be applied. They’re not scalable to something as large as the Great Barrier Reef, especially when the population is not there to implement them.
“What motivates me is that, even though it’s too early to say whether it will work or not, there’s very few things, other than a really dramatic global decline in greenhouse gas emissions – which I’m sceptical will happen in time – that I think can work.”