CDR Week 45/2026: A value-at-risk metric finally puts numbers on permanence
The most useful paper this week gives carbon dioxide removal (CDR) a single probabilistic number for permanence risk, and its first calibration puts a California forest project’s 95% carbon at risk above 70% over 200 years. Geological storage scores between 0.15% and 17% on the same scale, which makes the permanent versus non-permanent label look crude. Carbon at risk: permanence gets a metric A Nature Climate Change paper borrows value at risk from finance. It defines carbon at risk (CaR) as the probabilistic shortfall between contracted removals and realised storage at a chosen confidence level and time horizon. For forests, Monte Carlo runs driven by satellite fire data give a single-project 95% CaR above 70% over 200 years in California. For geological storage, the Storage Security Calculator gives 0.15% for well-regulated offshore sites and 17% for poorly regulated onshore ones. The authors say buffer pools are currently sized by convention, and they show that portfolios can manage tail risk cost-effectively. They also concede that early applications rest on assumptions until the underlying distributions can be estimated from observed data. My verdict: the metric is the right tool for buffer sizing and insurance pricing, but these figures are proof of concept, not ratings. ...