杏吧原创

Drax鈥檚 domes: where biomass is stored (Image: Paul Rogers/The Times)

Update: Since we published the article below, Drax energy company has pulled out of the White Rose carbon capture and storage project, citing the UK government鈥檚 decision to reduce subsidies for renewable energy. The company says it will continue converting parts of its existing power plant to burning biomass. It says this will lower its CO₂ emissions, but the prospect of negative emissions has for now ended

IT IS the dream scenario for fighting climate change: a power station that delivers negative emissions. And it could be coming to the UK, helped along by the growth of forests in the American South and some handy holes beneath the North Sea.

The giant coal power station at Drax in Yorkshire, with its 12 cooling towers, is one of the world鈥檚 largest greenhouse gas emitters. It sends some 23 million tonnes of carbon dioxide up its stacks each year, while supplying up to a tenth of the UK鈥檚 power.

Its owners are now planning to replace coal with wood pellets and bury the emissions. Combined with growing trees to replace all those burned, the mega-polluter could one day be transformed into the world鈥檚 largest industrial absorber of CO₂.

鈥淭his is a very exciting new technology,鈥� says of the National Non-Food Crops Centre, a consultancy that promotes bioenergy. 鈥淚t means we can actually reduce the volume of CO₂ in the atmosphere.鈥�

鈥淭his is a very exciting new technology. It means we can reduce the CO₂ volume in the atmosphere鈥�

The biomass side of the transformation is already under way. 鈥淪ince the beginning of July, half of Drax鈥檚 electricity has been generated by burning biomass, mostly from pine forests in the American Deep South,鈥� Drax鈥檚 vice-president for sustainability, Richard Peberdy, told me during a tour of those forests in Mississippi. The fourth of its six generators converts to biomass next year.

To feed the furnaces, the Drax company recently opened mills in Louisiana and Mississippi that turn logs cut from local pine forests into dried and compressed pellets, and a port at Baton Rouge, Louisiana, to ship them. It also buys hardwood pellets from elsewhere in the South, as well as Canadian sawdust, and will soon start burning wood from Brazil.

All told, 7 million tonnes of pellets will cross the Atlantic next year. Only about 5 per cent of Drax鈥檚 biomass comes from the UK, mostly straw and miscanthus.

Click on the interactive map below to explore carbon鈥檚 journey from American trees to Yorkshire power plant to storage under the North Sea (Storymap by Iona Twadell)

Next up is carbon capture and storage (CCS). Later this year, the UK government is expected to give the go-ahead for the 拢500-million , which from 2020 could capture 2 million tonnes of CO₂ annually from a new power plant burning coal and biomass, sending it down a 165-kilometre pipeline for burial under the North Sea.

With CO₂ burial up and running, the White Rose project will make electricity carbon-negative for the equivalent of around 600,000 homes. The pipeline will be big enough to take most of the rest of the CO₂ produced at Drax if it were captured in future.

The UN Intergovernmental Panel on Climate Change sees such measures as vital to curbing global warming. Its most recent report, published last year, concluded that widespread use of biomass with CCS would be needed to keep warming below 2 掳C.

鈥淭o arrest climate change we need negative carbon emissions. At the moment sustainable biomass with CCS is the leading technology to achieve this,鈥� says , a Drax director and chairman of Capture Power, the consortium behind White Rose.

The most pressing question for now is the cost in CO₂ emissions of producing the biomass. Drax says the energy needed to harvest, process and transport the wood will produce emissions just 14 per cent of those from burning coal. It also claims that all the carbon emitted by burning the wood can be recaptured by planting new trees.

However, Timothy Searchinger, an environmental analyst at Princeton University, and soak up CO₂ will increase the rate of global warming for several decades. And once trees have been felled, the land could be converted to other uses. A and Climate Change found that in the worst case, in which cut forests are replaced by cotton farms, burning biomass at Drax might end up emitting three times as much CO₂ as burning coal does.

What鈥檚 the catch?

But Drax is creating an economic incentive for planting and better forest management, Peberdy says. By providing a market, its plan could increase the carbon content of the forests. 鈥淲e believe forests are growing [in area] faster than they would be if we weren鈥檛 here.鈥�

Better than coal? (Image: Jez Coulson 鈥� The Sunday Times)

Dale Greene, dean of forestry at the University of Georgia, agrees. He says markets for timber products are the reason that southern forests have been growing in extent for decades. Mississippi has added 400,000 hectares, many on former cotton fields. 鈥淭he effect of Drax鈥檚 arrival has been to help keep the South forested. If we harvest more, we plant more and there is more carbon in the forest,鈥� he says.

Even so, trees would have to be planted on a vast amount of land to have any effect on climate change, says John Lanchbery of the RSPB. 鈥淭his would be land which is currently used for something else, like wildlife or farming,鈥� he adds.

Such land may be less diverse than the original forests. Scot Quaranda of the Dogwood Alliance, an environmental NGO, says that the more intensive forestry encouraged by Drax鈥檚 presence is replacing naturally regenerated diverse pine forests with uniform ranks of planted yellow pine.

Thomas Gasser of the Climate and Environmental Sciences Laboratory in Gif-sur-Yvette, France, backs the development of negative-emissions technologies, but adds that much more action is needed. 鈥淒rax is not a miraculous solution that spares us from shifting to a less carbon-based energy mix, and of reducing overall energy demand.鈥�

This article appeared in print under the headline 鈥淣egative emissions ahead鈥�