The knowledge that carbon dioxide build-up might cause serious problems was not restricted to files marked Top Secret. It was reported in the popular press from the early 1950s onwards (first about the work of Gilbert Plass, and then in connection with the International Geophysical Year of 1957-8. There were peaks and troughs in awareness. Until the late 1970s newspaper reports were always caveated with “scientists are not sure/some disagree”. By the late 1970s the frequency of newspaper articles was increasing, and the certainty of the scientists was firmer. This was usually (but not always) reflected in the reporting.