It is shown that during L-H and H-L transitions, soft terminations and strong ELM induced cooling, ce changes across most of the JET plasma column on a millisecond time scale (more than a hundred times faster than the energy confinement time tE) and usually simultaneously with the evolution of Ha radiation. The speed of response to these transitions is very much faster than previously observed. The jump in the electron conductivity can be easily obtained from experimental data. No scaling ce(Te, Te) can describe the observed electron temperature evolution during the transition. Possible explanations for the jump in ce are advanced.