On a very cold night, ice forms on the surface of a pond. The air above stays at a fixed temperature below $0^\circ\text{C}$, and the water below the ice stays at $0^\circ\text{C}$. The first $1\ \text{cm}$ of ice takes $2$ hours to form. How much longer does it take for the ice to grow from $1\ \text{cm}$ to $2\ \text{cm}$ thick?