The atmospheric detonations of nuclear weapons during tests in the 1950s and 1960s injected much radioactive debris into the troposphere and stratosphere. Figure 1 (compiled from Warner and Kirchmann, 2000), summarises the major explosions and illustrates the different phases of the tests, categorised by their yield. The large explosions emitted radioactivity and radioactive aerosols into the stratosphere, which was slowly transported into the troposphere, where it was removed by a combination of gravitational settling and cloud processes. One unexpected consequence was abundant experimental evidence for atmospheric circulation (WMO, 1965), but the radioactivity also directly affected atmospheric electricity. Radioactive aerosols emit high energy particles which form molecular ions, causing charging of the radioactive aerosols (Clement and Harrison, 1992). Ionisation generated by radioactivity and radioactive aerosols increases the electrical conductivity of air.