Carbon dioxide (CO2) is painted as the arch-villain in climate change, but how bad is it in reality? To give away the answer right at the start, it is not necessarily bad and is in fact an essential atmospheric constituent, one that has in a very real sense enabled life on planet Earth. The challenge with CO2 is one of those ‘too much of a good thing’ things…
CO2 is for sure a greenhouse gas, amongst a club of co-defendant evil-doers like NOx, SOx, methane, water vapour and a bunch of others, collectively referred to as Greenhouse Gases (GHG’s). Each contribute to warming of the planet to different extents but because the largest volume contributor is CO2, we compare the effects of each of the others against it. We use a measure called the Global Warming Potential. That measure shows how bad each unit of any particular GHG is compared to a unit of CO2, which allows us to come up with a Carbon Equivalent (CO2 equivalent more accurately) value for that gas… Methane for instance has a CO2 equivalent of 28, meaning each kg of methane has the same global warming effect as releasing 28kg of CO2. As that is the standard by which we measure how climate damaging our activity is, all roads in our simplified sustainability world and all climate crimes therefore, are represented by Carbon Dioxide…
But CO2 is not inherently a bad thing and in fact could be recognized as a bit of a hero. If you’re so inclined and punch the numbers, you can determine that the sun only supplies enough energy to the Earth to heat it up to approximately minus 18°C. We should therefore by rights be a lifeless frozen ice ball of a planet, which overall is a bit of a shocker the first time you work it out! But not to worry, GHG’s have come to our rescue. Visible light from the sun heats up the Earth’s surface, and in turn the heated surfaces radiate that energy out to space as infra-red radiation. Mixed in with all the other atmospheric gases, GHG’s act as reflective molecules specifically to this infrared radiation, delaying its immediate escape by bouncing the energy back and forth between land, sea and air before its eventual release to space. That causes the Earth as a system to get hotter than it would otherwise do and in the pre-industrial stable world (a world before climate change) this results in the predicted minus 18°C average temperature rising to approx. plus 15°C. Just in case there is any confusion here or something seems amiss, and to emphasise, we’re talking global average temperatures here. Weather systems and other planetary physics unevenly push the atmosphere around distributing heat differently within and between different regions, leading to our diverse, beautiful and distinctly non-average world. Some areas are hotter, some cooler, but we average things out when looking at a global scale. Importantly the amount of heat retained as a result of atmospheric GHG’s leads to an ample temperature to ensure liquid water and enable life. No more frigid snowball, time to rethink its criminal status - all hail CO2.
Pre-industrial levels of CO2 were about 240-280ppm, that means on average it made up less than 0.028% of the Earth’s atmosphere. At that level we had a equitable balance of received sunlight vs. retained heat and all was well – it was a stable system. (Just as a side observation, it is pretty staggering how little that CO2 percentage is and the scale of the effect it produces – nature is amazing huh?) Over the course of the industrial age we’ve managed to pump enough CO2 into the atmosphere to raise that level up to more than 420ppm, and that’s where all the trouble comes from. The balance has changed and we’re holding on to too much heat – we essentially added a thicker more densely populated GHG layer that is acting too effectively. The result is additional global warming and now quite noticeable climate change. Currently this ‘improved’ insulation around us has on average raised global temperature by between 1.2 to 1.5°C. It is obvious (at least it should be) that we can’t continue to pump out GHG’s and keep raising the temperature. It takes very little foresight to predict that what we’ve done, if continued, will really not go well for us.
So, ever the optimist, let’s look at solutions. Prevention is better than cure and as a community we’ve targeted the big dog first, energy, specifically fossil fuel energy. Oil, gas and coal are the largest overall GHG contributors by far and are viewed quite correctly as the main culprits of global warming. In some geographies coal which is the worst of all fossil fuel polluting sources (emitting somewhere around 2.5 tonnes of CO2 for every tonne of coal combusted) has now been fully retired, and less polluting natural gas has been widely adopted as a transition fuel until we can go to 100% renewables. (A quick clarification as some of you for sure questioned that last number I gave – burning 1 tonne of coal gives more than 1 tonne of GHG emissions, that doesn’t sound right, right? Well, the emissions are more than the mass of the original coal because the burning process leads to the combination of carbon and oxygen in the form of our old friend CO2, and it’s the captured oxygen molecules that add that extra mass to the emissions). Sadly, some areas have not transitioned and still rely heavily on coal, and some countries are still building coal plants, something that really is no longer supportable given the situation we find ourselves in. We should fix that really quite urgently.
Burning gas emits much lower levels of GHGs than coal so is a good step forward, but it is very much a half-step towards a clean energy system rather than a solution. If we can fix the dispatchability problem (i.e. we need “power on demand” which is tricky for renewable power generation systems) by adding sufficient storage to our grids, then additional gas power plants would become unnecessary, and a sustainable energy system comes into reach. COP28 set a target of tripling the renewable capacity globally by 2030 but actions so far are insufficient to meet that target. While the growth rate of renewables and the rapid cost reduction is great news and an impressive story of global scale human action, the transition needs to accelerate even more significantly if we’re to keep our temperature targets in sight.
In addition to energy, other GHG contributors include transport, agriculture and importantly industry. These make up the so called ‘hard to abate’ sectors - a club of activities that are tricky or currently uneconomical to make emissions free. Biofuels, ammonia, methanol and hydrogen are interesting options as replacement fuels in this sector, but they need further development to become widely economic, which is where our work in TII is focussing. Until we achieve economic levels for these replacements an option for reducing net CO2 emissions is Carbon Capture, Utilization, and Storage (CCUS). The ‘capture’ part of CCUS is carried out by separating CO2 from exhaust or flue gases so that they don’t make it into the atmosphere. Several technologies exist for doing this such as chemical solvents like amines, solid sorbents, or membranes that selectively remove the CO2 from the mixture of exhaust gases. Once captured, CO2 can be collected for storage, typically in secure geological sites where it will remain isolated for thousands of years and may over time in a slow natural process convert into rocks.
As an alternative to long term storage, the ‘utilization’ part of CCUS focuses on converting captured CO2 into valuable products. For example, CO2 may be used to produce synthetic fuels, chemicals, or building materials. Making use of CO2 needs significant research and development works though as at this stage the processes we’ve come up with are uneconomical. Perhaps in the future, if we have a renewably powered grid system and we use the excess (thus almost free) energy produced to power these processes, they might become viable. I remain firmly convinced that the person who invents a cost-effective use for CO2 will become a very rich human being, which certainly spurs on work in this area!
Whichever analysis I look at about achieving net-zero 2050, CCUS is an important part of our journey but CCUS in all its forms is currently expensive and energy intensive, so they all need further development – again, the team at TII are onto it, working on novel, low energy, high efficiency options to make this option economically viable. But as with all things to do with climate change and CO2 emissions reduction, the answer to how we fix it is we need to do everything – displace fossil fuels, make processes more fuel efficient, electrify whatever we can and then capture or offset what we can’t avoid… Reducing CO2 though is right at the centre of everything.