- 09 October 2013 by Michael Marshall
- Magazine issue 2938.
- For similar stories, visit the Climate Change Topic Guide
In conjunction with scientists attending that meeting, we’ve assessed the effectiveness – and cost – of the most likely methods. They include planting trees, shovelling crushed rock into the ocean, and building millions of chemical “sponges” to pull gas out of the air (see diagram to find out about each technique).
Alone, such CO2-suckers can only handle a fraction of emissions. So we will need several. “If we don’t employ some of these technologies, we will go above 2 °C,” says Richard Lampitt of the UK National Oceanography Centre in Southampton. “A programme of multiple negative emissions technologies could perhaps store a few billion tonnes of carbon per year by mid-century, and conceivably as much as 5 or 10 billion tonnes,” says John Shepherd, also at the UK National Oceanography Centre.
So by 2100, CO2-suckers might just mop up the equivalent of what our annual emissions are now. But there are big costs, even putting money to one side. The biological approaches will cover vast areas of land, pressurising farms and wildlife, while the high-tech approaches will burn lots of energy.
There are other problems. It is hard to verify if plants and oceans are trapping CO2. We need underground space to store the gas. And many techniques could harm ecosystems. Worse, pulling CO2 from the air makes it progressively harder to suck out more, so the methods get less efficient over time (Carbon Management, doi.org/dbkhqh). And models show that removing CO2 from the air affects land plants, too. “They grow more slowly and take up less carbon,” says Andreas Oschlies of the Helmholtz Centre for Ocean Research in Kiel, Germany.
That means we have to start soon: with immediate research to assess safety, and roll-out within 20 years. Some methods, like tree-planting, can begin now; others may be decades away (Process Safety and Environmental Protection, doi.org/n33). On top of all this, CO2-suckers are pointless unless paired with dramatic emissions cuts. If not, even a major programme of ocean liming beginning in 2020 would have little effect.
It ain’t cheap. As a rough estimate, it will cost several trillion dollars a year – a few per cent of global GDP. And it only makes economic sense with serious incentives, such as a high carbon price. But with a combination of CO2 reduction and geoengineering, we might just miss the worst of climate change. The bottom line is that CO2-suckers are essential, but we also need to ditch fossil fuels quickly. It’s that or climate havoc.
This article appeared in print under the headline “Transforming Earth”