Direct air capture machines suck carbon dioxide from the atmosphere. Are they part of the solution to climate change?

DAC technology has been mooted for years, but faced huge engineering challenges and, until recently, was dismissed as a costly fantasy. (Supplied: Climeworks)

On a barren lava plateau in Iceland stands an entirely new kind of industrial facility that sucks carbon dioxide from the air and traps it in stone.

The world's first commercial direct air capture (DAC) plant is designed to remove thousands of tonnes of greenhouse gas every year and then inject it deep underground.

Technology like this has been mooted for years but faced huge engineering challenges and, until recently, was dismissed as a costly fantasy.

Now the first plants are coming online, with the Intergovernmental Panel on Climate Change (IPCC) recognising that, even if the world reduces its ongoing emissions as quickly as possible, there will still be too much CO2 in the atmosphere to avoid catastrophic levels of global warming.

The DAC plant in Iceland is the first in the world to be operated commercially. (Supplied: Climeworks)

In short, the IPCC says, the world needs to both reduce future emissions and remove historical ones to reach a safe climate.

Experts say DAC could become a trillion-dollar global industry — if it can be deployed at scale.

So how does DAC work, what's the future of the carbon removal industry, and is this an opportunity for renewables-rich Australia?

Why not just plant more trees?

When Deanna D'Alessandro, a professor of chemistry at the University of Sydney, encountered the idea of mechanical carbon removal, she wondered if there wasn't a simpler solution.

A tree, of course, is a pre-existing and relatively cheap technology that sequesters CO2 in wood and other biomass.

When scaled up, it's called a forest.

"My first thought was why not plant more trees," Professor D'Alessandro said.

"And then I did the numbers and stood in awe of them."

By her own calculations, using reforesting to capture Australia's CO2 emissions for two years (about 1 billion tonnes), would require an area of land equivalent to the size of New South Wales.

DAC could do the same with 99.7 per cent less space, she said.

Mark Howden, director of the Climate Change Institute at the Australian National University, agrees.

"The science is very clear that to keep temperatures down to [an increase of] 1.5C, we not only need to reduce greenhouse gas emissions, we also have to absorb CO2 from the atmosphere," he said.

"It's increasingly clear that doing that just from planting trees and relying on farmers and soil carbon is not enough."

How does direct air capture work?

DAC is just one of several proposed technologies designed to remove emissions from the atmosphere, which also include repurposing offshore oil and gas platforms to grow seaweed and turn it into fire-resilient bricks.

So, DAC works a little bit like a household dehumidifier, but instead of stripping water out of the air, it removes carbon dioxide.

DAC would have to be scaled up enormously to be useful. (Supplied: Carbon Engineering)

The greatest challenge, says Professor D'Alessandro, is processing enough air to capture a significant amount of CO2, given the gas makes up just 0.04 per cent of the air we breathe.

There are generally two approaches.

In the first, a fan pulls air into a structure lined with thin plastic surfaces that have potassium hydroxide solution flowing over them.

The solution chemically binds with the CO2 molecules, removing them from the air and trapping them in the liquid solution as a carbonate salt.

In the second method, a sponge-like filter absorbs CO2 and is then reheated to release the gas into storage.

In the case of the plant in Iceland, the captured CO2 is injected about a kilometre underground into volcanic rock.

Over two years, it reacts with the basalt to form a solid carbonate material.

The captured carbon dioxide is injected into the ground at these nearby pods. (Getty Images: Arnaldur Halldorsson)

But underground storage isn't the only option, Professor Howden said.

"Probably the dumbest thing we can do with captured CO2 is put it in the ground," he said.

"To my mind, if we've gone to the bother of capturing CO2, why not treat it as a resource?"

Another DAC company, Canada's Carbon Engineering, plans to use captured CO2 as an input to make carbon-neutral synthetic fuels that can substitute for diesel, petrol or jet fuel.

Other proposals include using CO2 in cement production and plastics manufacturing, which could make buildings and water bottles carbon negative.

Is this any different to carbon capture and storage?

CCS involves capturing CO2 at the site of production, such as a gas liquefaction plant or coal-fired power station, and then pumping it deep underground.

Instead of filtering the air, it filters emissions from a smokestack.

Although the Australian government has singled CCS out as a priority technology for emissions reduction, critics have said it's a failure.

One of the major problems is CO2 leaking from underground reservoirs.

With DAC, there's a much lower risk of leakage, Professor Howden said.

"With standard CCS you're restricted in the geology to somewhere close to the point of combustion, whereas you can put a DAC system anywhere, so you find geology that's suitable and locate it there."

How much CO2 needs to be captured?

DAC would need to be enormously scaled up to be useful.

Even if the world reaches net zero by 2050, it will still be necessary to remove 5 to 14 billion tonnes of CO2 per year from the atmosphere from 2030 onwards to keep global warming below the 1.5C limit set by the Paris Agreement, according to a University of Melbourne report.

The DAC plant in Iceland, which is the world's biggest, can capture and remove 4,000 metric tonnes of CO2 a year.

That's about 10 million times less than annual global emissions.

At our current level of emissions, humanity is cancelling out the plant's yearly efforts every three seconds.

The "mechanical tree" concept uses wind, rather than fans, meaning a much lower energy cost. (Supplied: Silicon Kingdom Holdings)

Daniel Egger, the chief commercial officer of Climeworks, the operator of the Iceland facility, said the company was on track for "megaton capacity" by the second half of this decade.

"To be an effective solution for climate change, an entire carbon removal industry will need to develop over a period of the next 10 to 20 years, creating capacities of at least 5 billion tonnes of carbon removal by 2050," he said.

Professor Howden estimated DAC would ultimately account for a more modest amount of carbon removal.

"DAC of 1 to 1.5 billion tonnes of CO2 a year is potentially feasible," he said.

What does it cost?

DAC is currently prohibitively expensive, mainly due to the cost of energy.

Climeworks has priced its DAC offsets at about $US775 ($1,094) a tonne and says this will fall as low as $US250 ($353) by the end of the decade.

The US Department of Energy recently announced a goal of slashing the cost to $US100 per tonne ($141) by the end of the decade.

That's still a lot more expensive than offsetting CO2 by planting trees, which costs as little as $US20 ($28) per tonne.

Bushfires can release carbon sequestered in timber and undo millions of tonnes of offsets. (Supplied: Jochen Spencer)

So who's paying Climeworks a premium for DAC offsets?

"We have an array of corporate clients such as Stripe, Audi, Shopify, Microsoft, Swiss Re, Boston Consulting Group," Mr Egger said.

Microsoft, for instance, has committed to going carbon negative by 2030 and is investing $US1 billion ($1.4 billion) from 2020 to 2024 to "stimulate and accelerate the development of carbon removal technology."

Is Australia doing DAC?

There are several proposed DAC projects in Australia, but nothing yet at a commercial scale.

Energy giant Santos struck a deal with CSIRO last November to trial the government agency's new DAC technology in South Australia.

That same month, Elon Musk's philanthropic research foundation awarded a University of Sydney team $250,000 to develop solar-powered DAC modules the size and shape of a two-person tent.

An illustration of the solar-powered DAC module technology developed at University of Sydney. (Supplied: Southern Green Gas)

These could be deployed in non-arable parts of Australia with high levels of solar radiation, said Professor D'Alessandro, a member of the team.

A start-up named Southern Green Gas (SGG) plans to produce and deploy at least some of these modules by the end of the year.

Australia's abundant solar energy makes it an ideal location for DAC, Professor Howden said.

"DAC takes a lot of energy, so increasingly that will be sourced from renewables.

But, according to Professor Howden, for the industry to prosper, it will need a price on carbon and more research funding for universities.

It will also need public support, as the solar panels and wind-capture systems used for DAC will take up land.

"Would the public like those sorts of things dotted across the landscape?" Professor Howden said.

"We need to put in place [systems of support for DAC] early and that requires proactivity, which requires vision and foresight.

"If we're smart about this, this could be a billion-dollar earner for Australia."