Some may have said this, but they are just alarmists. Tornados, and the thunderstorms that they result from, derive their energy from the average energy of the atmosphere. The average energy of the atmosphere is proportional to the absolute temperature, so any change will be according to the ratio of the 2 temperatures involved.
So for a 1o change,
Tfinal/Tinitial = 292/291 = 0.0034 = 0.34%
So, 0.34%/oC is all the extra energy available to do what they claim. That's not a significant increase at all, and it's flat out fraud to claim that it is.
You're telling me. (:^D)