ORA-19602: cannot backup or copy active file in NOARCHIVELOG mode

RMAN> backup database;

Starting backup at 01-JAN-16
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=32 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 01/01/2016 09:20:49
ORA-19602: cannot backup or copy active file in NOARCHIVELOG mode
continuing other job steps, job failed will not be re-run
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
including current SPFILE in backup set
channel ORA_DISK_1: starting piece 1 at 01-JAN-16
channel ORA_DISK_1: finished piece 1 at 01-JAN-16
piece handle=/usr/oracle/app/flash_recovery_area/ORCL/backupset/2016_01_01/o1_mf_ncsnf_TAG20160101T092049_c8co3lgb_.bkp tag=TAG20160101T092049 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================

RMAN-03009: failure of backup command on ORA_DISK_1 channel at 01/01/2016 09:20:49
ORA-19602: cannot backup or copy active file in NOARCHIVELOG mode