Radiocarbon (^(14)C) is a critical tool for understanding the global carbon cycle. During the Anthropocene, two new processes influenced ^(14)C in atmospheric, land and ocean carbon reservoirs. First, ^(14)C-free carbon derived from fossil fuel burning has diluted ^(14)C, at rates that have accelerated with time. Second, ‘bomb’ ^(14)C produced by atmospheric nuclear weapon tests in the mid-twentieth century provided a global isotope tracer that is used to constrain rates of air-sea gas …