AN A300 'CARGO SMOKE WARNING - LAND NOW' ECAM ALERTED AS THE ACFT CLBED AFTER TKOF. THE CREW DECLARED AN EMER AND RETURNED TO LAND.

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WE LEFT ZZZ DELAYED APPROX 2 HRS DUE TO THE FIRST SNOW OF THE YR. THE CAPT FROM THE INBOUND FLT ARRANGED WITH SCHEDULING TO JUMPSEAT TO ZZZ1 WITH US; RATHER THAN LAYOVER THEN COMMERCIAL. ALL PROCS WERE NORMAL DURING GND OPS. WE DID HAVE TO DEICE AND REFERRED TO THE QRH FOR THE DEICE PROCS. THE CAPT COMMENTED 'I'M SURE YOU KNOW THESE BUT USE THE QRH ANYWAY.' I RAISED THE QRH SHOWING HIM I ALREADY HAD IT OUT. WE READ THE ENTIRE PROC BEFORE BEGINNING. ENG START WAS UNEVENTFUL. I NOTED THE ELAPSED TIME AFTER ENG START PRIOR TO TURNING THE AIR CONDITIONING PACKS ON AT JUST UNDER 2 MINS. WE TAXIED AND WAITED UNTIL NEAR THE RWY TO EXTEND THE SLATS FOR TKOF. ACCOMPLISHED THE BEFORE TKOF CHKLIST AND DEPARTED RWY 28R. ACCOMPLISHED AFTER TKOF CHKLIST. EVERYTHING WAS UNEVENTFUL UNTIL CLBING THROUGH 10500 FT WHEN WE GOT A MOMENTARY ECAM. MID 1 MAIN DECK LOOP FAULT; BUT IT JUST FLASHED ON AND IMMEDIATELY DISAPPEARED. (NO STATUS.) THEN PASSING 10700 FT IT CAME BACK WITH A REPETITIVE CHIME AND CARGO SMOKE WARNING LAND ASAP. I CONTINUED TO FLY; THE CAPT DIRECTED THE ENTIRE CREW TO DON OXYGEN AND THEN RAN THE ECAM. WE LEVELED OFF AT 11000 FT AND INFORMED APCH WE HAD A PROB. THE JUMPSEATER CONFIRMED THE CARGO COMPARTMENT WAS FULL OF WHAT APPEARED TO BE MIST FROM THE TOP OF THE CANS. WE GOT VECTORS BACK FOR THE ILS TO RWY. THE CAPT COMPLETED THE ECAM AS WELL AS THE APCH AND LNDG CHKLISTS. I FLEW THE APCH WHICH HE MONITORED. ON FINAL CAPT ASKED THE TWR IF THE FIRE TRUCKS WERE STANDING BY AND THEY SAID YES. WE BROKE OUT AT MINIMUMS AND LANDED NORMALLY. THE CAPT ASKED THE TWR IF THEY SAW ANY SMOKE COMING FROM THE ACFT AND THEY SAID NO. WE CLRED THE RWY ON A TXWY WHERE A FIRE TRUCK WAS STANDING BY. THE CAPT TOLD THE TWR IF THE FIRE DEPT COULD CHK US OUT WE WOULD TAKE THE AIRPLANE BACK TO PARKING. THE FIRE DEPT CHKED US OUT AND SAID WE COULD TAXI TO THE RAMP AND THEY WOULD FOLLOW. UPON PARKING AND NORMAL SHUTDOWN THE FIRE DEPT USED INFRARED EQUIP TO CONFIRM THERE WERE NO HOT SPOTS. THE FIRE CHIEF RELEASED THE ACFT. THE CAPT WROTE UP THE AIR TURN BACK AND CARGO SMOKE WARNING IN THE LOGBOOK.