Since he caused an ice age i'll assume that he lowered the temp of the atmosphere to -25 C.
Mass of the atmosphere = 5.15e18 kg (source )
c = 1000 j/kg*K
ΔΤ = T(final) - T(initial) = 288 - 248 = -40 K (average temperature of the earth is around 15 C)
Q = m*c*ΔΤ
Q = 2.06e23 Joules (49.2 Teratons of TNT) Country level