A new study from the University of Ottawa shows that sugar maples in Gatineau Park, Quebec, retained elevated carbon-14 from Cold War nuclear bomb tests for about six decades, long after atmospheric levels returned to normal. The leaves peaked at 842 parts per thousand above the reference level in 1964, but only matched the pre-bomb baseline around 2024, roughly two years after the atmosphere did. Researchers say the delay comes from trees recycling older stored carbon to grow new leaves, not from atmospheric conditions. The findings matter for climate science because scientists often use carbon-14 in leaves and tree rings to reconstruct past atmospheric CO2 levels. If that record lags by a few years, historical climate reconstructions need to be corrected by plant species. The study also notes that fossil fuel burning, which releases carbon-14-free CO2, helped dilute the bomb pulse signal over time, making these leaves a 65-year diary of both nuclear testing and the fossil fuel era.
