Geoengineering has been advocated as a solution to climate chaos. Mirrors in space to reflect sunlight, human induced algal blooms to absorb carbon, and cloud seeding have all been proposed as ways to manage an impending climate crisis.
Many of these options, however, attempt to deal with the effects of climate change, not its causes. Their benefits are fleeting, they depend on continuous programmes of intervention and they have unacceptable side-effects at local and regional levels. They are unlikely to gain political support and will not succeed.
Prevention, not cure
We need solutions that deal with the causes of climate change - rising concentrations of greenhouse gases in the atmosphere - not just crudely with its symptoms, and in a way that can be socially, politically and environmentally acceptable. We are already at 391 parts per million (ppm) of CO2 in the atmosphere and this is increasing at 2 ppm annually. This gives us less than 30 years before we breach the 450 ppm threshold, where average global temperature are likely to rise by 2 degrees or more. There is clearly an urgent need to develop such solutions.
Fortunately, there are a suite of emerging technologies that can scrub carbon from the air and these could have a role in helping to reduce the stock of CO2 in the atmosphere. “Negative emission” technologies (NETs), combined with robust mitigation efforts, could help us tackle climate change.
The Grantham Institute for Climate Change at Imperial College London have just published a new report that investigates how NETs could be deployed to successfully scrub emissions from the atmosphere at a scale able to make a meaningful difference to climate change and in a way that might be acceptable to society.
The study looked at how five emergent NETs could be scaled up so as to successfully scrub 0.1 ppm of CO2 from the atmosphere each year. This is equivalent to annually removing 781 MtCO2 and is roughly 1.5 times the annual emissions of the UK.
The technologies studied - direct air capture, the soda-lime process, augmented ocean disposal, biochar and bio-energy carbon capture and storage (BECCS) - could remove 0.1 ppm annually at estimated annual costs of between $46bn and $120bn.
Each option has strengths and weaknesses. Three of the technologies - direct air capture, the soda-lime process and BECCS - are heavily dependent on the deployment of carbon capture and storage (CCS) technology to successfully transport and sequester carbon once it has been extracted from the atmosphere. This reinforces the need for investment in CCS infrastructure over the long term and an emphasis on BECCS in particular, as this has been entirely ignored in recent competitions to fund CCS demonstration plants. CCS could ultimately be for the atmospheric scrubbing of CO2, opposed to merely reducing emissions from carbon intensive processes.
Some of the technologies have important co-benefits that could make them relatively more attractive. Biochar can make an effective fertiliser substitute, potentially reducing costs for agriculture and BECCs generates electricity and heat that can be sold to offset its increased cost. Augmented ocean disposal can help to reverse ocean acidification, which is damaging marine ecosystems around the world and worsening as the climate changes.
The study also highlights the lack of clarity over mechanisms to support NETs. The sooner investors have visibility on how mature and operational NET projects might be remunerated, via the carbon market for instance, the easier it will be to attract capital into earlier stages of research, development and deployment. It is, therefore, important to develop support mechanisms soon so as to provide visibility on the route to market and encourage investment today. Policy makers need to think urgently about how support for NETs might work and also reflect on how they should be best regulated.
Despite the potential, none of the NET options are straightforward and there are serious challenges associated with their deployment at 0.1 ppm scale, even if a combination of the technologies are utilised at lower levels. New industries would need to be created, land would need to be found and competition with agriculture and other sectors managed. We would also need to find ways to minimise localised impacts and ensure that NETs genuinely deliver lifecycle negative emissions, without compromising other important environmental objectives, such as biodiversity conversation.
So while NETs could potentially make our task easier in some ways and allow us to come back from the brink after we breach a 450 ppm limit, it does not let us off the hook in terms of the need to dramatically reduce the flow of global emissions into the atmosphere. To be successful we must both reduce emissions quickly and act to scrub some carbon from the air as well.
Ben Caldecott is Head of Policy at Climate Change Capital