University of Ottawa researchers found maple leaves in Gatineau Park still carried carbon-14 from Cold War-era nuclear testing until May 2024. The signal came from atmospheric bomb tests in the 1950s and 1960s, which roughly doubled radiocarbon levels. After decades of uptake by plants and oceans, plus dilution from fossil fuel CO2 that contains no radiocarbon, the leaves returned to pre-bomb levels. On a carbon site, the interesting part is what erased the bomb signal. Fossil fuel emissions are now large enough to mask a global radiocarbon spike that took 65 years to fade. That makes carbon-14 less useful for tracing recent CO2, and it shows how long-term environmental monitoring can capture changes that short studies miss.
