A CRJ Flight Crew returned to their departure airport when the aircraft failed to pressurize. Maintenance discovered an improperly closed cargo door that was not detected by the aircraft door warning system.

Narrative

We were climbing through 10;000 feet when we received a CABIN ALT caution message followed by a CABIN ALT warning message. The Captain was the flying pilot and disconnected the autopilot so he could stop the aircraft from climbing. ATC allowed us to stop the climb at 10;000 feet. The Captain then assumed control of the radios and flight controls and told me to perform the QRH procedures. I followed all QRH procedures; but we still couldn't get the aircraft to pressurize. The door synoptic page said that all of the doors were closed. The Captain told ATC that we were going to return to our departure airport but would need to burn fuel so we wouldn't land above 47;000 pounds. I notified the Flight Attendant of the situation and then made an announcement to the passengers letting them know why we were returning. We then landed and maintenance met the aircraft. Upon inspection of the aircraft maintenance informed us that the cargo door was NOT closed properly even though the door synoptic page said that it was closed. The improper closing of the cargo door prevented the aircraft from pressurizing normally.