Data from the Optical Transient Detector lightning sensor are analysed to investigate the hypothesis that global lightning activity will increase should the average global temperature increase. It is shown that changes in global monthly land lightning activity are well correlated with changes in global monthly land wet-bulb temperatures. the correlation is strongest in the northern hemisphere and weak in the southern hemisphere. the conclusion is that a high land-area to sea-area ratio is necessary for a good correlation. Contrary to expectation, the tropics show no correlation. the results predict that a change in the average land wet-bulb temperature of the globe of just 1K would result in a change in lightning activity of about 40%.