Answer
Work is done on the gas and the internal energy increases.
Work Step by Step
We use the first law of thermodynamics.
$$\Delta U = Q-W$$
If the gas is compressed adiabatically, Q=0.
$$\Delta U = -W$$
The compression means that work was done on the gas, so the work done by the system, W, is negative.
We see that the change in internal energy is a positive quantity, meaning the internal energy of the gas increased, so the temperature increased.
