Fifteen years ago large-scale removal of CO2 from the atmosphere was considered a form of geo-engineering that would only be used as a last resort if global climate policies failed. Today it is critical to the net zero strategies of governments and businesses. Its watershed moment came in 2015 when negotiators at the COP21 climate conference conceded that emission reductions alone would not sufficiently constrain increases in average global temperature. Decarbonisation would have to be supplemented with carbon sequestration i.e. ‘negative emissions’. The more we overshoot our carbon budgets, the more CO2 we will need to recapture.
Climate modelling suggests that by 2050 around 6 billion tonnes of CO2 will have to be removed from the atmosphere annually, that’s roughly 14 times as much CO2 as the UK emitted in 2021 and 600,000 times more than sequestered annually by the 18 ‘direct air capture’ plants operating globally in 2022. A ramp-up of this magnitude will be daunting. The National Infrastructure Commission predicts that ‘engineered’ greenhouse gas removal will become ‘a major new infrastructure sector for the UK over the coming decades’.
As CO2 constitutes only 0.04% of the atmosphere, you have to filter a lot of air, using complex chemistry and huge amounts of energy, to extract and purify it for use or storage. It takes around 15 Royal Albert Halls’ of air to capture one tonne of CO2. Where possible we should capture concentrated streams of CO2 from chimneys and exhaust pipes before they’re released.
Bio-energy carbon capture (BECC) relies on vegetation to extract the CO2, but it would require vast tracks of land to operate at the necessary scale and confidence that future deforestation, forest fires and storm damage will not seriously impair this nature-based sequestration. One study also found that end-to-end BECC supply chains from forest to underground storage emitted more CO2 than the amount sequestered! Fortunately software tools have been developed to configure these chains in ways that maximise net CO2 removals.
Value chains will also have to be optimised for sequestered CO2 used in the production of products such as building materials, polymers, proteins and e-fuels. A new US study estimates there is a ‘global utilization potential’ for around 5% of total CO2 emissions, if only they could be economically captured and distributed at scale.
This highlights the pivotal role that logistics will play in the planetary-level sequestration that will be needed to rescue us from what the UN Secretary General recently called ‘climate hell’. It would be simplified if the capture and processing of CO2 could be ‘co-located’ with plants using it as a feedstock or sites for permanent ‘geologic’ storage. Research suggests, however, that much sequestered CO2 will have to be moved long distances. It has been estimated that Europe will require an 11-17,000 km network of CO2 pipelines by 2050. The US already has 5150 miles of CO2 pipeline but most of the gas it carries is used to squeeze more oil out of the ground – the last thing we should do with sequestered CO2!
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