Negative emissions tech: can more trees, carbon capture or biochar solve our CO2 problem?

In the 2015 Paris climate agreement, 195 nations committed to limit global warming to two degrees above pre-industrial levels. But some, like Eelco Rohling, professor of ocean and climate change at the Australian National University’s research school of earth sciences, now argue that this target cannot be achieved unless ways to remove huge amounts of carbon dioxide from the atmosphere are found, and emissions are slashed.

This is where negative emissions technologies come in. The term covers everything from reforestation projects to seeding the stratosphere with sulphates or fertilising the ocean with iron fillings.

It’s controversial – not least because of the chequered history of geoengineering-type projects, but also because of concerns it will grant governments and industry a licence to continue with business as usual. But many argue we no longer have a choice.

“Most things are not applied yet on larger scales but we have a pretty good feeling of things that will work and we can quantify roughly how much carbon we should be able to remove from the atmosphere with them,” says Rohling.

The scale of the task is staggering, says Dr Pep Canadell, from the global carbon project at CSIRO.

“The models are basically asking for removing carbon dioxide from the atmosphere which will be equivalent of one-quarter of all carbon emissions at present,” he says.

This amounts to about 10 billion tonnes of carbon dioxide removed from the atmosphere and disposed of each year.

The least controversial method of doing this is deceptively simple: plant more trees. “We have lost a lot of density of carbon in the landscapes because of deforestation and degradation. We have depleted carbon in the soils in all the problem areas of the world,” Canadell says. “What are the opportunities to bring some of this carbon back?”

Again, the scale of reforestation efforts needed to make a dent in atmospheric carbon dioxide is substantial.

“We would need as many as three Indias worth of land globally – and good quality land, not marginal land,” Canadell says. Reforestation also needs enough water, and needs to be done in such a way that it enriches the soil and ecosystems, not deplete them.

The fact that so many soils are carbon-depleted by intensive agriculture offers a way to tackle two environment challenges at the same time. Biochar is a form of charcoal produced by heating plant material in the absence of oxygen. Agricultural waste, which would otherwise be a major source of greenhouse gas emissions if burnt, could instead be turned into a biochar – a process that produces more energy than it consumes – and the biochar could then be used to enrich agricultural soils with carbon. Research suggests that biochars not only boost crop yields, but could lock away carbon for several thousand years.

Another approach designed to lock away carbon while also helping depleted soils is enhanced weathering.

Olivine refers to a group of silicate minerals that react with carbon dioxide to form other compounds. 

Read more https://www.theguardian.com/sustainable-business/2017/may/05/negative-emissions-tech-can-more-trees-carbon-capture-or-biochar-solve-our-co2-problem

Courtesy of Guardian News & Media Ltd