During compression from a given initial volume to a smaller final volume, the pressure increases. In an adiabatic compression, the temperature also increases, which causes the pressure to rise more steeply compared to an isothermal compression where the temperature remains constant. On a $P$-$V$ indicator diagram, the adiabatic curve lies above the isothermal curve for compression. Since the magnitude of work done on the gas is equal to the area under the $P$-$V$ curve, the area under the adiabatic curve is greater. Therefore, more work is required for adiabatic compression than for isothermal compression.