A refrigerator appliance may include a cabinet, a door, a humidity sensor, and a controller. The cabinet may define a chilled chamber. The door may be rotatably hinged to the cabinet to move between an open position and a closed position. The humidity sensor may be mounted to the cabinet within the chilled chamber. The controller may be operably coupled to the humidity sensor. The controller may be configured to initiate an operation routine. The operation routine may include detecting a first humidity level within the cabinet in response to the door being in the open position, detecting a second humidity level within the cabinet when the door is in the closed position following detecting the first humidity level, determining an ambient humidity level outside of the cabinet based on the first and second humidity levels, and transmitting the determined ambient humidity level to a secondary appliance.