Explanation:

if the experiment is conducted in a sufficiently cold environment, then the cubes will not generally be joined after merely pressing them together with the hands.
It will be necessary to conduce an experiment to see at what temperature they will fail to join. Such an experiment could start at minus 5 degrees Celsius since it seems reasonable to suppose that is cold enough.

At sufficiently high temperatures (surely room temperature but possibly much lower), the cubes will join because they are already starting to melt at the surfaces exposed to the air.

By pressing them together, the touching surfaces are no longer exposed to relatively warm air and so they are effectively cooled by the surrounding ice. If the cooling is sufficient then the melted surfaces will re-freeze. Since the surfaces are in contact with each other, they will be joined.