IPCC author team consults in Mexico City on methodology for CO2 removal and storage

More than 120 authors of the Intergovernmental Panel on Climate Change (IPCC) are meeting in Mexico City from 11 to 14 August to discuss the First Order Draft of a methodological report intended to clarify the accounting of CO2 removal as well as the capture, utilization and storage of carbon dioxide (CDR/CCUS). The report is being prepared by the Task Force on National Greenhouse Gas Inventories and is scheduled for 2027.

Why the methodology matters

National greenhouse gas inventories are the basis for climate policy, international reporting and the review of emissions targets. A consistent, scientifically robust methodology for CO2 removals and storage creates comparability between countries and projects — from government reports to voluntary mitigation programs. Inconsistent rules, overestimations or double counting undermine the credibility of climate action.

Points of contention on the agenda

The discussions center on measurability, uncertainties and the temporal dimension of reliable storage (permanence). While geological storage can potentially remain stable over long periods, biological sinks — such as afforestation — carry risks from fire, pests or land-use change.

Other core questions concern accounting rules: How are life-cycle emissions included? What thresholds and definitions apply to leakage effects? How can double counting between the country of origin, buyers and international mechanisms be avoided? And how are baselines and additionality determined, i.e., the demonstration that projects remove CO2 beyond business-as-usual developments?

Terms and technologies: CDR and CCUS

CDR refers to measures that remove CO2 from the atmosphere — for example, afforestation, improved soil management, bioenergy with carbon capture and storage (BECCS), direct air capture or enhanced rock weathering. CCUS encompasses the capture of CO2 at emission sources, its utilization and/or storage. Not every CCUS application results in a net removal from the atmosphere; that depends on the accounting rules and the permanence of storage.

Risks and social aspects

Large-scale CDR projects can create trade-offs in land use, biodiversity and water resources. Geological storage requires strict safety standards to minimize risks such as induced seismicity or impacts on groundwater. Questions of justice and participation are also central: the rights of local communities, inclusion of indigenous groups and clear requirements for monitoring, reporting and verification.

Process and outlook

The current draft represents an early step in the IPCC process. The First Order Draft will be followed by expert and government reviews and revisions before the final report is published in 2027. In Mexico City, wording will be refined, methodological gaps addressed and responsibilities clarified.

International dimension

The author team brings together expertise from atmospheric sciences, geology, engineering, ecology, economics and the social sciences. The broad composition aims to ensure that the guidance remains applicable across different geographic, economic and legal contexts — from countries with limited monitoring capacity to industrialized nations with extensive technical infrastructure. Clear, verifiable rules increase transparency around CO2 removals and storage — but do not replace the need to rapidly and permanently reduce emissions.