A lake has a layer of ice on its surface of area 1800 m², thickness 0.025 m and density 920 kg/m³ (mass of ice = 41400 kg). At night, the temperature of the ice on the lake falls by 3.5 °C. The specific heat capacity of ice is 2.1 × 10³ J/kg °C.

Calculate the change in energy as the temperature falls.