In 2013, the UN Intergovernmental Panel on Climate Change (IPCC) released a comprehensive report outlining many approaches to CDR (section 6.5 starting on page 546). The report is quite technical, but has a number of interesting charts that help explain CDR:
1. A diagram showing the global carbon cycle, helping to show where carbon goes when it gets emitted into the atmosphere. The finding that a significant portion of CO2 can take thousands of years leave the atmosphere makes the case for developing CDR solutions all the more imperative.
Note: the diagram shows carbon fluxes, not CO2 fluxes. To convert to the more commonly-cited CO2 figure, multiple the these numbers by 3.67 (which represents the weight of a CO2 molecule compared to a molecule of pure C).
2. A table outlining many of the various CDR approaches, which vary quite widely in their methods.
3. A table showing the potential for different CDR approaches. PgC, or petagrams carbon are equal to 1 gigatonne (1 billon metric tonnes) of carbon. Annual emissions are on the order of 10 PgC per year, meaning that it is technically possible to remove A LOT of carbon from the atmosphere with currently identified techniques.