To build an artificial lake in the city, the temperature is adjusted by using the large specific heat capacity of water. If the mass of an artificial lake is 1× 107Kg, the water temperature is.

Because of the large specific heat capacity of water, during the day, water with the same quality absorbs the same heat than sand, and the temperature of water rises less; The same heat is released at night, and the temperature of water is reduced less, which makes the temperature difference between day and night small and can effectively adjust the climate;

Heat absorbed by water:

Q suction =cm△t=4.2× 103J/(kg? ℃)× 1× 107kg×2℃= 8.4× 10 10J。

So the answer is: big, 8.4× 10 10.