Different techniques can, and have been, used in the removal of carbon from the atmosphere and its subsequentstorage. Some CDR activities aim to enhance existing sink mechanisms in the Earth system:

• CDR measures aiming to enhance biological carbon uptake processes include the expansion of existing terrestrial or coastal vegetated ecosystems (a/reforestation, coastal blue carbon enhancement, respectively). 
• CDR measures aiming to enhance chemical carbon uptake processes include the increase of weathering processes by adding alkaline materials on land or on the surface ocean (terrestrial weathering or ocean alkalinity enhancement, respectively).

Geological carbon dioxide removal (CDR) refers to the process of capturing CO₂ from the atmosphere (and more recently from the ocean surface) and storing it permanently underground in geological formations such as deep saline aquifers or depleted oil and gas reservoirs.

The different CDR techniques can have very different mitigation potential, associated storage timescale and technical/political readiness. Most techniques considered more conventional (such as forest management or coastal restoration) can be implemented readily, but typically with a storage potential shorter than that of other novel techniques (for example ocean alkalinity enhancement or direact air capture and storage). Investments in CDR research and improved development of CDR application have been increasing over the past decade, yet gaps in policy clarifications, procedure for monitoring, reporting and verification, as well as process-understanding on individual CDR potential in future scenarios remain.

This phase of CDRMIP aims to solve many of the questions posed by the latter source of uncertainty, allowing for a better understanding of CDR efficiency and side-effects, for both individual CDR options and CDR portfolios, and for distinct possible futures.