There are persistent rumors that during the seventies South Africa together with Israel conducted an atmospheric nuclear test in the South Atlantic and the world did not notice it. This is a very large planet and although our detection technologies have improved a good deal since the Seventies, we are still more guessing than measuring. Our atmosphere is a big place too and its dynamics are still poorly understood. Most are conjecture and assumptions. We should go back and measure more instead of pretending our opinions to be facts.
The uncertainty makes it hard for governments to make concrete pledges—and to hold them accountable.