The arrival of Arthur 'Bomber' Harris to take charge of Bomber Command heralded a new attitude. He was in favour of revenge on a massive scale. He accepted the target statistics and started a system of night 'area' bombing as an alternative to individual target raids which previously had proved disastrous for the British. In July 1943 at Hamburg, at least 30,000 people died, many of them killed by the heat which, in places, reached an estimated 1000ºC. German civilian morale, for the first time, was shattered.

Source: http://www.theworldatwar.com/