In the last Sunday Science, I focussed on the latest IPCC report and the urgency of taking action to reduce global warming. I also bemoaned the lack of action so far, and the recent direction of various administrations in the UK, US and Australia which is making the situation worse. It’s enough to make anyone despair. So this week I’m going to focus on things we can do if humanity doesn’t get it’s act together in time to curb CO2 emissions.
In this brief piece, I won’t consider big geoengineering ideas. These essentially aim to mitigate climate change by reducing the amount of sunlight that reaches the earth, e.g. by injecting aerosols into the atmosphere. These are all big-scale projects that are only at a very early research stage, and I don’t like them, basically because I don’t think trying to fix climate change by messing with the climate even more is a great idea. Moreover, we simply don’t have the time to fully research and implement such projects before things reach the danger point. However, if you’d like to explore this further, carbon brief has an excellent page here.
There are basically two things you can do to lower carbon dioxide emissions if you still want to carry on polluting. Firstly, you can capture the waste carbon dioxide and use it for something else. I’m excluding carbon capture and storage from this, because that tends to fall under the umbrella of action taken to mitigate climate change, and ultimately you are still ending up with waste CO2, just not in the atmosphere. In this case, I’m considering not storage but actually using the carbon dioxide. Secondly, you can try and design systems to suck carbon dioxide already in the atmosphere out of it, which does fall under the category of “geoengineering” but one which I have a bit more time for as it’s working to directly reverse the problem created in the first place.
It’s realistic to say that most countries will in the near future be relying on an energy mix provided partly by renewables, but partly by fossil fuels that will produce waste CO2. So let’s consider what we can do to use that CO2 instead of pumping it into the atmosphere and heating up the planet. There’s a nice review I found on current and future technologies here (unfortunately paywalled).
The main difficulty with doing anything with CO2 is that it is a very unreactive, stable molecule: in order to convert it to something else, you need energy and catalysts, and obviously if you use up too much energy then you’re basically back to square one because you’ll need to burn more fossil fuels to make more energy, which makes more CO2…etc.
The authors discuss the electrochemical conversion of CO2 to fuels and feedstocks—the CO2 reduction reaction (CO2RR). In this process, CO2 is converted to hydrocarbons using water and (renewable) electricity. CO2 would need to be captured from emission sources using carbon capture technologies, but those are reaching practical application in their development. The hydrocarbons and other potentially useful molecules that could be generated include hydrogen, methane, and ethane (excellent fuels) and ethylene and ethanol which are useful chemical feedstocks to make other products.
Electrochemical conversion like this is the closest to being realised: photocatalytic conversion, which essentially mimics photosynthesis by using semiconductor catalysts in gas-phase CO2 reactors is also a possibility. This would also use only solar radiation as a fuel, and thus not be dependent on an electricity source. These are their two main possible technologies, there are others outlined below.
I’ll freely admit that their analysis of the costs and efficiency of various catalytic systems is rather beyond my chemistry knowledge, but the point is that at least some of these are within reach practically as well as theoretically.
Here’s their lovely summary figure of the options to catalytically convert carbon:
What if that’s not enough? What if we find we urgently need to decrease the amount of CO2 already in the atmosphere? Can we do that? Well, we can already do carbon capture and storage, as mentioned – but that’s from the very high concentrations present in flue gases of power stations. Can we suck it out the atmosphere, where it’s currently at 400 parts per million? Granted we should focus on capturing it from power plants first, it’s still an interesting possibility, but whether it could ever be done on a scale to actually significantly reduce the concentration in the entire atmosphere is rather out there.
Nevertheless, two prototype power plants have actually managed to do so, and on a scale where it’s almost commercially viable: the CO2 captured is used either to convert to fuel or used directly as a plant growth booster in commercial greenhouses. Carbon Engineering’s plant in Canada is currently pulling about a tonne of CO2 from the atmosphere a day (so a minuscule amount compared to emissions, but nevertheless about the same as a typical car might emit when driven about 5,000 kilometres). It works by using fans to push air through towers containing potassium hydroxide solution, which reacts with CO2 to form potassium carbonate. Another plant absorbs the CO2 in granules and uses the heat from waste incineration to drive it off and capture it. There’s another nice summary piece here.
Incidentally, whilst researching for this piece, I found this nice little blog post about a “self-healing” polymer which takes carbon dioxide out of the air to repair itself and may one day be on the outside of your buildings. So that’s quite neat, on a small scale.
None of these things are anywhere near enough. The carbon capture however could help buy us time, which is the critical limiting factor in implementing the real changes that need to be made in the next 12 years (according to the IPCC) if we are to avert climate disaster. I should also stress that all these ideas are things that can be done in addition to aiming towards zero emissions. These technologies are certainly not replacements: they can mitigate some of the problems, they are not a solution: the only solution is to decarbonise the economy, which means renewable energy, electric cars, reforestation, etc. The naysayers should be ignored. As this pithy and well-known cartoon puts it: why wouldn’t we create a better, cleaner world? Even if you take out the benefits in stopping climate change, all the other positives are more than worth it.
This artist’s rendering shows Carbon Engineering’s design for an ‘air contactor’ to pull carbon dioxide from the atmosphere. Credit: Carbon Engineering. With the graphical abstract from Busheyev et al, 2018 (Joule).
Bushuyev et al, 2018, What Should We Make with CO2 and How Can We Make It? Joule. https://doi.org/10.1016/j.joule.2017.09.003
Keith, et al, 2018. A Process for Capturing CO2 from the Atmosphere. Joule. https://doi.org/10.1016/j.joule.2018.05.006 (2018).
Nature News, June 2018.