The 2015 Paris Agreement established the global ambition to “achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases (GHG) in the second half of this century”. This is more commonly referred to as “net zero GHG emissions”. To reach net zero targets, substantial gross emissions reductions of over 90% across all sectors (transport, energy, waste, industry, AFOLU) will be needed.

Realistically, only a small and limited amount of carbon dioxide removal (CDR) – defined as the removal and permanent storage of atmospheric carbon dioxide (CO₂) in stable reservoirs – can be achieved. Nonetheless, CDR will have a crucial role in counterbalancing residual emissions. Options include emerging negative emissions technologies and practices (NETPs) that enhance natural processes or use novel approaches. Each method spans a range of technological readiness, has potential physical limitations, resource dependencies, adverse impacts, and co-benefits. Given these trade-offs, as well as the challenges for storage permanence, liability for any reversals, and limits to upscaling removals, a diverse portfolio is required; no one technology or practice alone can address the challenge of removing the required amount of CO₂ by 2050. Moreover, the risks that come with relying on one single approach, or a small subset of approaches, must be minimised.

The handbook discusses a list of concepts relevant to CDR and explores six different NETPs: biochar, biomass with carbon capture and storage (BioCCS), direct air capture with carbon capture and storage (DACCS), terrestrial enhanced weathering, afforestation and reforestation, and soil carbon sequestration. It is aimed at policymakers, NGOs, journalists, and members of the public with an interest in CDR policy making. As such, it seeks to provide a robust summary of the core principles, concepts, technologies and practices underpinning CDR.