Climate change plan B: going negative

Monday, December 7, 2015

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If world leaders can't agree to drastically reduce greenhouse gas emissions, technologies that remove carbon from the atmosphere could be our only hope for avoiding extreme climate change. Gregg Borschmann reports.

With global greenhouse gas emissions projected to continue rising for at least the next decade, scientists and policy makers are quietly but increasingly focused on so-called 'negative emissions' strategies.

These range from simply planting more trees through to technologies like carbon sequestration and even negative emissions concrete.

They're all designed to drawn carbon out of the atmosphere—and they're an increasingly important 'plan B' if the world is to limit global warming to two degrees. It's now thought that without these negative emissions scenarios, the world will overshoot two degrees of warming and enter the territory of dangerous climate change.

Last year, the Climate Institute looked at the potential for negative emissions and concluded that the strategies are essential for a safe climate outcome.

'What we found is that if you exclude negative emission technologies—like storing carbon in the land or capturing it in the atmosphere and storing it geologically through carbon capture and storage (CCS)—then you substantially increase the risk that we won't get on a trajectory to two degrees,' says Erwin Jackson the institute's deputy CEO.

Unfortunately, it may already be too late to avoid a two degree increase in global temperatures.

'If you walked onto an aeroplane, you'd probably want a 99.99 percent confidence that the plane wasn't going to crash,' says David Karoly, professor of atmospheric science at Melbourne University.

'Unfortunately, we're already past the amount of greenhouse gases in the atmosphere that gives us a very high confidence we're not going to exceed two degrees, that we aren't going to exceed the threshold for dangerous climate change.'

Karoly, a board member on the Climate Change Authority, says negative emissions technologies are now the world's best option.

'We have to go to negative emissions so that we suck out carbon dioxide from the atmosphere. It's only by [doing this] that we'll be able to have high confidence of avoiding two degrees and even to go down [further] and stabilise the climate at less than two degrees.'

As the world seeks to hammer out a new global climate treaty in Paris to limit global warming, what's not widely known is that two degree goal on the table only has a 66 per cent probability of success. In other words, even if world leaders can agree on new, ambitious pledges to cut pollution, there's a one in three chance that the world will overshoot two degrees.

It's these odds that are increasing interest in negative emissions technologies.

Image: Negative emissions technologies (Source: Canadell and Schulze (2014) in Nature Communications DOI 10.1038/ncomms6282)

Professor Tim Flannery, chair of the Climate Council, says some of these technologies are unusual. He points to 'carbon negative concrete' as an example

'Negative emissions concrete absorbs CO2 into its structure as it matures,' he says. 'That could be reducing emissions on the gigatonne scale by 2050 if we introduced a carbon price or a cap and trade [emissions trading scheme] into the concrete sector.'

Many negative emissions strategies rely on carbon capture and storage. It's long been thought by many that CCS could save the coal industry, but Flannery says it won't work in that case, though it could with other emissions sources.

'Conventional carbon capture and storage for coal, I think, has now been shown that it doesn't have a future in economic terms,' he says. 'The two [CCS coal] plants that have been built were behind budget, behind time and I don't see anyone lining up now to replicate them. [But] there are other options for CCS that are really interesting.

'One may be associated with seaweed farming, the storage of CO2 in marine sediments down two to three kilometres depth. The thing about those depths is the column of water above tends to pressurise the CO2 and keep it in liquid form and it forms a solid eventually in those sediments.

'The second option might be using the Antarctic's ice cap for the capture of carbon. CO2 falls as snow over the Antarctic when conditions get very cold even today. We could precipitate that snow by chilling the air in parts, [then] burying it and storing it.  These are options for many decades away, they're just desktop studies at the moment. But I think CCS may have a more interesting future than some of us imagined.'

Image: Relationship between average and extreme temperatures in the future (Climate Commission 2013b, modified from IPCC 2007)

For his part, the Climate Institute's Erwin Jackson is not prepared to write off CCS for the coal industry, at least for the moment. However, he agrees with Flannery that the technology could have a number of applications.

'There's potentially innovative strategies where you use bio-energy, for example, to draw carbon out of the atmosphere, then use that as an energy source, capturing the carbon from the burning of those materials and then storing it geologically, like we do and have been doing for decades in the oil and gas industry. We use, capture and store carbon in underground reservoirs'.

In Paris, Environment Minister Greg Hunt said Australia's work on sequestering carbon in rural landscapes—planting trees, storing carbon in soils, fire management in savannah landscapes—is seen as 'world leading'.

And as both major parties move toward 'net zero emissions' in coming decades, there will be a lot more of it.

In a major report this year, Australian National Outlook 2050, the CSIRO estimated that more than one third of Australia's future carbon emissions could be sequestered in restored bushlands and plantations across less productive agricultural zones in Queensland, NSW, Victoria and Tasmania.

Steve Hatfield-Dodds is chief scientist, integration science and public policy, for the CSIRO.

'You're talking up to 20 per cent of cleared land returning to biodiversity plantings in our scenarios and then another 40 per cent on top of that could go to carbon plantings—that's the technical potential that could be realised if Australia chose to go that way.

'You could see lots of areas either return to bush, as they were 100 years ago, or you could see plantations there. Plantations deliver a bit more carbon, so they make more money on that front, but they don't have the biodiversity benefits and they might not have tourism spin-offs.'

'If the world takes more decisive action on reducing emissions, then storing carbon in plants and soils is going to have economic value. Once the [carbon] price gets up towards $45, then you [will] start to see substantial action across the landscape'.

Jackson, however, cautions that there are risks to CCS.

'You don't want to be in a situation in the land sector where you're storing large amounts of carbon or developing large amounts of bio-energy where you're actually impacting on natural environments and also impacting on farming communities,' he says.

And it's not just rural landscapes that could be affected.

Karoly is deeply concerned about research into another Plan B for cooling the earth—geo-engineering, or shooting aerosols into the stratosphere.

'It changes rainfall patterns all around the world and leads to massive drought, particularly in the tropics,' hypothesises Karoly. 'It has adverse health impacts if these particles are injected into the lower atmosphere. If these particles are injected into the stratosphere, it causes enhanced stratospheric ozone depletion which causes increases in UV radiation which causes increases in skin cancer.'

'It's often been thought of as curing the symptoms, rather than curing the problem itself. Unfortunately, this cure might actually have a worse impact. It might kill the patient as well as slowing down global warming. I'm not sure that killing the patient is a good solution in terms of solving climate change.'