Carbon Dioxide Removal (CDR): what would good look like?

I have spent the last 6 months trying to learn about the climate crisis, hoping eventually to contribute to solving it as an operator and an investor. I am by no means an expert and have still a huge amount to learn. This post is an attempt at simplifying and sharing some of my learnings and nascent beliefs. All errors are my own and I welcome correction and feedback.

For a summary of why I ended up looking into CDR, please check the previous post here.

Unlike current carbon permits which are mostly about avoiding emissions (preventing trees from being burned for instance), CDR represents carbon dioxide that was emitted and is now sucked back from the atmosphere. If you want a deeper overview of what this looks like you should read this and that. For the super short version, stay here.

In essence, CDR is about finding a way to capture the carbon from the atmosphere and then sequester it for the long term in a form that is not atmospheric gas.

To simplify things, there are 4 negative emissions paths (experts would probably have a different taxonomy, but I found this one to be useful):

  • BECCS, which is essentially growing huge amounts of biomass (e.g. trees), burning it to generate energy, capturing the carbon in the process, mixing it with water, pumping it at high pressure in the crust of the earth and storing it there on geological time frame.
  • DACCS, which is using various kinds of materials that captures the CO2 from the atmosphere, usually heating that material to separate the carbon, mix it with water and pump it in the crust of the earth
  • Land management, which is essentially growing biomass and managing the land in a way that increases the carbon content of an ecosystem while absorbing carbon directly from the atmosphere (e.g. reforest land, recarbonize soil, etc.)
  • Mineralization, which is about accelerating the rate of carbonisation of certain rocks so carbon is being captured on a monthly or yearly time frame rather than on geological time frames
Cutting edge carbon removal technology

It is important to point out that:

  • All of these methods are already being applied at some scale and there are many academics and entrepreneurs trying to validate, refine and scale solutions. A few random and non exhaustive examples: here (Commercial DACCS), here (Commercial land management and mineralisation. Disclosure: I am an investor in that company) and here (One of the leading research labs on mineralization)
  • But none of these methods seem to be able to scale on their own to the 15Gt per year that we seem to need. Most have a theoretical potential of a few Gt per year each
  • Approaches can be mixed to form hybrid solutions: for instance Enhanced weathering is a land-based method that captures carbon and helps recarbonize the soil but it is essentially a mineralization solution. Some companies are also working on hybrids between mineralization and DACCS (For instance Heirloom or Origen).

And all of these methods have substantial unresolved problems:

  • BECCS will require amounts of water and land to work at scale that is likely to conflict with agriculture and other key human needs
  • DACCS require staggering amounts of energy to work, at a time where 80% of global electricity energy mix is based on fossil fuels and needs to be replaced
  • Land management has a verification process that is questionable at best and very expensive and
  • It is far from certain that mineralization can be sped up enough to matter at big scale
Cutting edge carbon removal technology (BECCS power plant)

For a solution to be credible over the long term, there is a set of attributes that matter. We do not know which solution will end up being successful but we know that it will need several of the following attributes:

  • Sequester carbon for thousands of years or more without requiring intervention from people (from that point of view, a tree on its own is not ideal on its own as once it dies — usually after 60y — the carbon is released back into the atmosphere). This is called permanence
  • Have a low cost and high trustworthiness of verification. The ideal here is something meterable, with results stable over time, where the carbon captured can be measured directly and is not based on statistical models, complicated life cycle analysis or control-group based testing
  • Doesn’t compete with humans for something fundamental: that probably means that the energy requirement or land requirement of carbon capture has to be kept to a manageable size, compatible with a population in the 8–10 billion range
  • The right solution would also be able to capture carbon at scale (hundreds of millions of tons of CO2 — or Megaton — or even billions — or Gigaton) at a cost per ton at or below $100. Incidentally, it means a market worth a total of $1.5t, the same order of magnitude as the fossil fuel industry.
  • In the short term, if the solution could operate at megaton scale without requiring a large, shared CO2 pipeline and storage infrastructure (CCS), it would probably speed up the roll out as it would remove a dependency that has been on governments’ lap for quite a while.

It is worth noting that some people are already buying negative emissions permits along these lines (https://stripe.com/blog/first-negative-emissions-purchases) although speaking with these folks suggest that the current global capacity of rigorous negative emissions is probably in the order of magnitude of hundreds of kilotons per year of CO2e, to be compared with a target of 15Gt per year by 2050.

Sam and I spent the last few months speaking and working with academics to investigate paths, setting up experiments and using these criteria as a yardstick to assess which pathway would provide the most long term potential with the lowest short term scientific risk. I’ll share what we learned in the next post.

Scale-up CEO. Looking at climate-related companies. Ex-CEO @Skimlinks (Acq. in May 2020), Board member at VC-backed companies, investor. Aspiring pianist.