New view of Tweed Valley’s attraction

Australia’s Tweed Valley region, in northern NSW, boasts world-class surf breaks and sub-tropical rainforest – and according to new research, it is also the perfect natural laboratory to pull carbon out of the atmosphere.

To meet the Paris Agreement and prevent the average global temperature from rising more than two degrees Celsius above pre-industrial levels, the world needs to rapidly slash emissions. But current national commitments are falling dismally short of the target.

Research is attempting to pick up the slack by developing methods to actively remove carbon dioxide from the atmosphere, using both technology and enhanced natural processes.

One proposed method involves ramping up the natural weathering of silicate rocks like olivine or basalt, formed by ancient volcanic activity.

“When common rocks, known as olivine, chemically break down, they absorb carbon dioxide to form carbonates that can then be washed into the oceans,” explains lead author Kyle Manley, a postgraduate researcher now at the University of California Irvine, US.

Plankton use these dissolved carbonates to build their calcium carbonate shells or skeletons. When they die and float down to the sea floor, their bodies accumulate into thick layers of deep-sea sediments that keep the carbon locked away for millions of years.

Previous research has suggested that olivine weathering could be harnessed to remove millions of tonnes of carbon from the atmosphere every year, but those ideas have not yet been tested on a large scale.

Now, geoscientists from the University of Sydney have used computer modelling to study a local region with the potential to test this method of carbon capture: the 1326-square-kilometre Tweed catchment area, which is near the site of a large extinct volcano.

Their results are published in the journal Frontiers in Earth Sciences.

“We ran seven scenarios up to 2100 and 2500 to see how much carbon might be absorbed in different climatic conditions,” explains co-author Tristan Salles from the University of Sydney.

The scenarios attempt to describe the complex connections between weathering and sea-level rise predicted to occur along the Tweed coast.

“Future climate change will increase the rate of weathering in this area and distribute enormous amounts of eroded volcanic debris across the coastal floodplain and along the coast,” says co-author Dietmar Müller, also from the University of Sydney.

Although coastal erosion from rising seas will counter some of the effects, all seven scenarios estimated that millions of tonnes of carbon dioxide could be absorbed by olivine weathering by the end of the century.

“But this is a drop in the ocean of the billions of tonnes a year of carbon pollution expected to be emitted over the coming decades and centuries,” cautions Salles.

The United Nations estimates that in a mid-range scenario, where we cut emissions but not as drastically as needed, humans will emit 70 billion tonnes of carbon per year by 2100. A site like the Tweed River region would therefore absorb less than 0.1 percent of carbon emissions.

Pep Canadell, a researcher at the CSIRO Climate Science Centre who was not involved in the study, agrees that scale of removal is an issue.

“Australia is emitting about 530,000,000 tonnes per year of CO₂ equivalent from human activities,” Canadell says – while the modelling predicts the Tweed region would absorb an average of 780,000 tonnes of carbon per year.

Although every effort helps, he says that this region “won’t change a bit the overall trajectory of the human influence in the accumulation of atmospheric CO₂.”

However, Müller points out that studying smaller areas is still important to better understand the efficiency of carbon sequestration processed outside of the lab.

“Nobody is suggesting that carbon sequestration via olivine weathering will solve our problems,” says Müller.

“[But] natural laboratories need to be investigated to find out whether this process could be turned into a negative emissions technology. The idea is that volcanic olivine sand would be spread across coastal areas to create green sand beaches. Waves help break down the rock, accelerating a reaction that ultimately removes CO₂ from the atmosphere.”

The modelling in this study could also help identify other regions ideal for enhanced natural carbon sequestration – and, as a by-product, model how these landscapes will be transformed as the seas rise.

“In the most extreme climate change scenario… the morphology of the NSW north coast and Gold Coast will be unrecognisable by 2500,” says Müller.

“The coast will be a series of embayments, estuaries and lagoons, with dark volcanic sand changing the white colour of beaches forever. If this is not what we want to see happening, we need to make a much more serious effort to reduce carbon emissions.”