It is unrealistic to expect that humanity will be able to develop enough carbon sequestration in time to hit our climate targets. This emphasises the need to electrify and decarbonise faster.

When you burn a hydrocarbon, it becomes three times bigger as a molecule, because you add two oxygen atoms to each carbon atom. It also becomes about 5000 times larger because it becomes a gas (CO 2 ), where in most cases it started as a liquid or a solid. The fossil-fuel industry is invested in the idea that you can keep burning their product, provided you capture that CO2 and bury it. To capture the CO2 requires expensive filtration equipment that, even if you exclude the cost of capital, requires a great deal of energy to operate. So the idea amounts to using more energy to capture the CO2 , then yet more energy to compress the CO2 , then yet more energy again to transport that CO2 to somewhere the geological formations allow you to hide it for hundreds or thousands of years while you hope it turns into a rock.

Today we pull roughly 10 billion tonnes of fossil fuel out of the ground each year. It becomes 30 billion tonnes of CO2. The fossil-fuel industry wants you to believe they can keep emitting a whole bunch more because we’ll be able to sequester it, but the world is already counting on a physically unrealistic amount of sequestering to compensate for ‘overshoot’ – the fact that we’ll go past our 1.5°C target and have to use negative emissions.

In a nutshell, carbon sequestration can only make fossil fuels more expensive, which will make them even less competitive with cheaper renewables. We can’t do enough carbon sequestration to maintain even a fraction of the existing fossil-fuel industry. It is unlikely the world will be able to do enough carbon sequestration just to offset our overshoot, let alone to allow for continued offsetting of fossil fuels. Electrification will be cheaper anyway, and will reduce the amount of energy we need by half while improving our quality of life.

We are already geoengineering. Burning fossil fuels is geoengineering that gives us climate change. The question is, can we geoengineer for good instead?

Geoengineering is not a decarbonisation strategy. It is a hope to control the temperature of the earth while giving up on CO2 strategy. Many of the early arguments for studying geoengineering were that we should know how, just in case the world turns out to be apathetic about climate change. We now know multiple paths to geoengineering climate change: most of them amount to managing the incoming flux of energy from the sun. You have probably heard of these ideas - giant space mirrors, scattering reflective particles in the atmosphere, artificially-generated clouds. In an ecosystem as complex as that of earth, they will all have unintended effects. 

Geoengineering would also make us dependent on always needing geoengineering in the future. It's a bit like using liposuction as the solution to obesity when you're just going to keep eating cheeseburgers. Even if it works, and we do it, we can't afford to take the pressure off the better, cleaner solutions proposed. 

The problems of trying to control the climate are many. Who sets the temperature? Low-lying islanders and people who love coral or northern Europeans who might benefit from a bit more climate change? We don’t really know all of the unintended consequences - environmental, social, or political.

It is a good idea to study geoengineering schemes, and it does help us understand earth systems better, but this is not a realistic permanent solution. It could draw large amounts of resources away from technologies we already know can solve the problem.