Carbon removal sucks

Carbon dioxide removal systems, taking carbon dioxide gas out of the atmosphere, are touted as techno-fixes for global warming, but in practice they can sometimes put more green house gases into the air net than they take out, a recent study claims. 

Carbon capture and storage (CCS) is perhaps the most familiar of the carbon removal options. With CCS, the CO2 produced by coal- or gas-fired power stations is collected and then stored, although, so far, most of the few systems that have been built simply use it for enhanced oil recovery (EOR)- squeezing more oil out of near empty oil wells. In that case, when the oil is burnt, you get more CO2 back again. Some Direct Air Capture (DAC) systems have been built with a storage option, but the proportion of CO2 in the atmosphere is much lower than that in power station exhausts, and DAC use a lot of energy to extract CO2 from it: so we are no further forward if this is fossil energy, and not much further forward if this is renewable energy – it would a probably have been more effective to use that energy direct so as the avoid producing CO2 in the first place. We also have to find somewhere to store the CO2 reliably – for ever. As an alternative, it is possible to use the CO2 captured by DAC or by fossil CCS, along with hydrogen from some source, to make new synfuels, but you need a lot of energy to do this and when the synfuels are burnt, you get the CO2 back again. 

The basic problem is that there is little commercial incentive to bury carbon, which is a quite costly and uncertain process, so that at present, instead, the emphasis is on trying to find ways to commercialize captured carbon dioxide- for example by using it to make salable fuel.  However, that undermines any net carbon reduction effect. Indeed, if it involves or enables the use of fossil fuel, it can make the situation worse, adding more CO2 net. 

The new paper by Sekera & Lichtenberger puts some numbers to it.  For example, it says CCS with EOR emits between 1.4 and 4.7 tonnes of the gas for each tonne removed. Fossil powered Direct Air Capture (DAC), emits 1.4-3.5 tonnes for each tonne it recovers. Just sticking with DAC might work if green power could be used to drive it, but the amount of energy needed to make a difference to the climate would be gigantic. As People and Planet note, capturing 1 gigatonne of CO2 (1 GtCO2, just one-fortieth of current global CO2 emissions) would need nearly twice the amount of wind and solar electricity now produced globally and vast areas for the equipment. Some say that biomass combustion with carbon capture and storage (BECCS) would be a good carbon negative energy supply option, but you would need vast areas for biomass growing & CO2 storage. The later could be avoided if the CO2 could be used to make a saleable fuel, but then the whole process would no longer be carbon negative. 

Most government scenarios have CCS/CCUS as quite central, but the new paper says we have to move away from the drive to commercialise CO2: ‘dedicated storage, not sale, of captured CO2 is the only assured way that mechanical–chemical methods could meet the collective biophysical need of absolute atmospheric CO2  reduction, governments should approach CO2 removal and storage as a public service, like water treatment or waste disposal. It should be operated in the public interest, with CO2 captured from the air being sequestered for dedicated, permanent storage.’                  

However, most greens seem to have concluded that, even with storage, in general carbon removal and processing is not on environmentally. It is just an expensive and difficult way to allow us to keep burning fossil fuel or compensate for past combustion, and this new paper has been welcomed as far as it goes. But its analysis seems to suggest that carbon removal with full storage can still be condoned, and views differ on that and on other carbon removal options. 

For example, as I noted a chapter in a recent book, even if emissions can be reduced this way to some extent (CCS never captures 100%, more like 80-90% net in practice), some say that, in opportunity cost terms, the net impact over time may be negative in carbon removal terms: investing in carbon removal will detract from investing in zero carbon renewables.  The compromise position is that a bit of CCS for hard-to-decarbonise industry may be OK, and some CCU in special sectors too, even some BECCS, but most greens would no doubt say, let’s just get on with renewables and energy saving to avoid emissions. And if you want to store carbon, then go for trees and natural biological methods of carbon removal -  although they too have limits. There may not be enough space for the scale of tree growth needed to deal with past and projected future carbon emissions, certainly not indefinitely. Basically, although it makes sense to plant trees (there are other benefit from reafforestation), and we should draw down as much CO2 as we can effectively, however we try to do it, we can’t soak up all our carbon sins for ever. 

The analysis above does conflict with one of the prescriptions explored in the otherwise generally excellent new book by Kim Stanley Robinson ‘The Ministry for the Future’. This science fiction novel looks at what might be done given the ostensible failure of the current UNFCCC/COP approach to climate change and eco-crises. Its main focus is political and economic change, but it does also push some geoengineering ‘tech fixes’, including carbon removal via CCS/DAC, with, rather simplistically, the vast amount of CO2 collected being stored somewhere as ‘dry ice’ (frozen CO2). That would need not just space but also a huge amount of energy. Maybe as much as for running the block-chain carbon-coin system that is also proposed. Though it could be that renewables could provide it, as is explicitly proposed (but abandoned) in the book for pumping sea water back up to freeze on the melting Antarctic ice-sheet. That’s one of the few direct mentions the book makes of renewables, though presumably they would be widely and directly used for power, heat and transport in its proposed future world. Whether it also makes sense to use them for carbon removal is debatable- that may not be the most efficient use of inevitably limited green power sources, and, in any case, as is admitted in the book, carbon storage is not a viable, secure long-term option.  

Back in the real world, the UK National Infrastructure Commission (NIC) is seeking evidence on using carbon capture and storage (CCS) technologies for the removal and storage of greenhouse gases in the UK- focusing on DACS and BECCS. It will be interesting to see what they come up with.