I'm not a physicist, so I won't attempt to explain the principle in that matter. When you pitch up, as in a climb, you are changing the PLANE OF ROTATION of the prop. Assuming the prop rpm is constant, the force applied will be shifted 90 degrees in the direction of prop rotation. That shift in force is felt as a left turning tendency. Get a bicycle wheel, spin it fast, then sit on an office swivel chair with your feet up and holding the wheel in front as a propeller. Move the wheel through different planes of motion. The chair will turn.