The total activity of 137Cs discharged into the atmosphere by all 535 atmospheric nuclear explosions was around 1018 Bq. This is much more than from the Chernobyl and Fukushima accidents. For Fukushima, the amount of 137Cs released is estimated to be 1.2 × 1016 Bq and this is about 14% of the emission estimated for the Chernobyl accident (Steinhauser et al., 2014). Some of the 137Cs inventory in the environment has already decayed but the half-life of 30.04 years implies that a large portion persists. Today’s remaining ¹³⁷Cs inventory from atmospheric nuclear tests is on the order of 2–3 × 1017 Bq. A more precise estimate will be determined by a project…