Rated 16 A continuously at ambient temperatures from 40 °C through 55 °C; above that it derates to 15 A at 60 °C, 65 °C, and 70 °C. That flat 16 A band from 40 to 55 °C is useful in a warm panel — you don't lose headroom until the enclosure interior passes 55 °C.
Breaking capacity — the number that decides fault clearance
The 121 kA figure at 240 V is exceptionally high for a 1-pole 16 A MCCB — it means this breaker can safely interrupt a fault on a high-capacity 240 V supply without the arc re-striking or the case rupturing. At 415 V the 9 kA rating is more typical for a 16 A frame; coordination studies should use the 415 V value for three-phase line-to-line faults.