Removing greenhouse gases


Engineering the removal of carbon dioxide from the atmosphere is essential if we are to meet the targets laid down in the 2015 Paris Agreement for reducing greenhouse gas emissions. There is an overwhelming scientific consensus that, in the fight against climate change, the world cannot rely on simply reducing carbon dioxide (CO2) emissions. We need to remove greenhouse gases from the atmosphere directly. Published in September, an important report from the Royal Academy of Engineering and the Royal Society, Greenhouse gas removal, presents an ambitious plan setting out how the UK can lead the way in deploying such technologies so that the country is carbon neutral by 2050.

Dr Scott Steedman FREng

Dr Scott Steedman CBE FREng

The idea of greenhouse gas removal (GGR) is not new, but technology development, let alone implementation, has been painfully slow. Government and industry urgently need to understand the effectiveness and cost of full-scale GGR projects so that the UK can devise a robust strategy for developing and implementing the technologies.

One of the technologies that will play a critical role in GGR is carbon capture and storage (CCS). CCS involves removing carbon from carbon-rich gases, often pre- or post-combustion at power stations, and storing the CO2 underground (‘Carbon capture and storage’, Ingenia 27; ‘Underground coal gasification’, Ingenia 43).

The history of CCS in the UK has not been promising. In 2012, the Department of Energy and Climate Change (now part of the Department for Business, Energy and Industrial Strategy) launched a competition to support CCS technologies to extract and store CO2. The programme was cancelled in 2015, despite proposals for full-scale trials in North Yorkshire and Aberdeenshire. Meanwhile, other countries are making real progress. The Academy’s report cites two projects, one in Canada and one in Texas, that are at the demonstration stage and many others are reported to be in operation or under construction worldwide.

There are other ways to remove CO2 from the atmosphere, but their capacity is limited. The most obvious GGR technique that the UK could implement immediately is increased forestation and wetland development. The largest wetland element could be restoration of salt marshes around the coast. Carbon could also be captured in soil by adapting farming practices on cropland or grassland. But there is limited land available. Even if the area of forestry land in the UK increased by over a third, to 5% of the total land area, the report suggests that this would contribute less than 12% of the UK’s 2050 target for CO2 removal. We need other ways to meet that target.

The built environment is an obvious place to look for ways to store carbon. Using more wood in construction, such as timber-framed housing, would be an easy win. Concrete is a major source of CO2 emissions in the construction industry where a net carbon saving could be achieved by using different aggregates or novel chemistries for cement production. But again, the total achieveable contribution is likely to be low, around 4% of the UK target.

Other ideas are still at an early stage. One proposal is to spread silicates, potentially derived from industrial waste, on arable land as rock dust, which would react with carbon dioxide in the atmosphere and accelerate natural soil weathering. However, it will take extensive research, development and field trials before this could be licensed.  

It is clear that if the UK is to meet its 2050 targets, reducing carbon emissions will not be sufficient. Removal of CO2 from the atmosphere is also essential. Most of this reduction will have to be achieved by using CCS, contributing up to 60% of the total target. The favoured approach is to deploy CCS on biomass power plants, with plants generating energy by burning agricultural, forestry or municipal waste, bringing a double benefit. However, the Academy’s report concludes that even this will not be enough and that CO2 may need to be extracted directly from the air. Pilot projects are already operating in other countries but, as with CCS, not in the UK.

In turbulent political times it is difficult to keep an eye on the long term, but ignoring the problem of climate change is unlikely to lead to a cost-effective outcome for industry and society in the UK. Government needs to heed this important report and urgently re-open the file on CCS.

Dr Scott Steedman CBE FREng

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