Probably, above 100 Degree Celsius.
The higher the current, the more likely it is lethal. Since current is proportional to voltage when resistance is fixed (ohm's law), high voltage is an indirect risk for producing higher currents.
V1 / T1 = V2 / T2
3.5 / 20 = 3 / T2
T2 = 17.1 C
Earths magnetic field is formed mostly by
B. SOLAR WIND