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Railway cargo cars carrying coal
Credit: satephoto/Shutterstock
3 February 2015 7:00

Coal carbon capture could increase future climate risks, study finds

Simon Evans


Simon Evans

03.02.2015 | 7:00am
CoalCoal carbon capture could increase future climate risks, study finds

Coal-fired power stations should be replaced by low-carbon energy sources rather than retrofitted with carbon capture and storage (CCS), according to new research from the University of Oxford.

The study dents the idea that coal can be compatible with climate action as long as it uses CCS. It says finite CCS capacity should be held in reserve in case negative emissions technologies are needed to return dangerous greenhouse gas concentrations to a safe level after 2050.

The new report on Stranded Carbon Assets and Negative Emissions Technologies is published today by the Smith School of Enterprise and the Environment.

Stranded assets

The idea that companies could be sitting on fossil fuel assets they can’t burn if the world tackles climate change has now  hit the mainstream. One study found nearly 90 per cent of the world’s coal reserves are  unburnable if we’re to avoid dangerous warming.

A counter-argument is that firms could carry on burning coal while capturing the emissions through CCS. Smith School analysis suggests this has the potential to capture 125 gigatonnes of carbon dioxide in total  by 2050, against today’s  annual coal emissions of around 12 gigatonnes.

So coal plants could have another 10 years of business-as-usual operation without eating into carbon budgets, if they used all available CCS capacity to capture their emissions.

Negative emissions technologies that remove carbon from the atmosphere could extend the operating life of coal plants even further, again assuming only coal emissions are offset.

The Smith School report looks at what types of negative emissions technologies are available and how much breathing space they might inject into the  carbon budget for two degrees.

Negative emissions

The idea behind negative emissions is that even if atmospheric greenhouse gas levels overshoot safe limits, new technologies or different ways of managing land could be used to pull back from the brink.

Options include reforestation to lock up carbon in wood, soil enhancement to store it in the ground or biomass energy with CCS, known as BECCS, where carbon-rich biomass is burned to generate energy and the emissions are locked away underground. Direct air capture, where a chemical reaction is used to suck carbon dioxide from the air, is another possibility.

In total, these technologies could remove up to another 120 gigatonnes of carbon dioxide by 2050, the Smith School paper finds. This is around another 10 years of current annual global coal emissions.

By 2100, negative emissions schemes could remove a further 1,000 gigatonnes, though the study notes this figure is much more uncertain and represents an extremely challenging scenario. Reaching this sort of scale would require deployment on an “improbably massive scale”, comparable to today’s global energy or agricultural systems.

For example, the amount of carbon dioxide captured and stored under this scenario in 2050 would be around 7,000 million tonnes. This exceeds the 4,000 million tonnes of oil extracted each year by an industry that employs several million people around the world..

Good news for coal?

Despite this challenging outlook, the large potential of negative emissions technologies might appear to be good news for owners of coal mines and coal-fired power stations.

But the reports says:

“It would be foolhardy for an owner or operator of carbon-intensive assets to assume that negative emissions technologies will fundamentally alter the carbon budgets that they face due to climate policy and regulation.”

Ben Caldecott, Smith School programme director, tells Carbon Brief:

“The coal industry keeps saying CCS will allow them to keep combusting coal. But if you combine the space in carbon budgets created by both CCS and negative emissions you do not create enough space for the coal industry to keep going like business as usual.”

Under business as usual, for the coal industry could use up all the available negative emissions and CCS breathing space out to 2050 within a couple of decades. More importantly, that breathing space should be reserved for other sectors rather than being used up by coal, Caldecott’s report argues.

Back from the brink

There are geological, political and economic constraints on the amount of carbon dioxide that can be stored using CCS, the report says. If coal uses it up then there will be less of this finite space available to use for negative emissions techniques, such as BECCS, should the world need to pull back after overshooting its carbon budget.

Caldecott tells Carbon Brief:

“The thing that was most surprising to me was this very clear trade off between coal CCS today and negative emissions as an emergency option post 2050.”

The report says the breathing space would be better used as offsets for sectors such as aviation and agriculture, which have emissions that are technically challenging to avoid. Coal emissions, in contrast, can be removed by generating power from low-carbon energy source such as nuclear or renewables.

Preparing to be able to use negative emissions as an emergency measure post-2050 means the technology would need to be tested and developed, Caldecott says. But he says that’s a very different proposition from retrofitting lots of coal-fired power stations with CCS.

Climate insurance

The findings come at a bad time for the coal industry. Several of the largest firms in the sector have lost 60 per cent of their value in the past year. Now they’re being told that even CCS won’t save them from the strictures of climate action, because CCS capacity should be set aside as insurance against a failure to cut global emissions fast enough.

There’s clearly a tricky balancing act around the report’s conclusions. The world’s first full-scale CCS plant is a coal-fired power station in Canada. If coal is excluded from CCS, it’s unlikely the technology would be mature enough to be part of a rapid roll out of negative emissions schemes that could put the brakes on dangerous warming later this century.

That’s why other negative emissions schemes like reforestation would be a safer bet, the Smith School says: they have other benefits, cost less to get going and do not rely on CCS to achieve their aims.

Main image: Railway cargo cars carrying coal.
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