With every mission impossible film comes more action, more impossible missions and a fresh new 'do. So, if you followed along with the action series you'll notice Ethan Hunt's hair pattern.
Mission Impossible 1
Short Buzz Cut
Why it makes sense? It was built for endurance. Otherwise, he hair would be flying around and covering his eye when he's floating into the vault (slide to see video).
Mission: Impossible II
What's cooler than riding a motorcycle with a swift long hair? Also, keep an eye out for those luscious hair flips. It's definitely made for the runway. Proof? Take a look at the intro scene. No one can rock climb so elegantly and fashionably like Ethan Hunt.
Mission Impossible 3
Lots of intense fight scenes in this one and having short hair gives Ethan Hunt more speed and precision. He really doesn't have time to stop and flip his hair out of his face. This is why Owen Davian (Philip Seymour Hoffman) lost.
Just kidding. But it makes sense, right?
Mission Impossible 4: Ghost Protocol
It's like combining all the previous haircut in one. Not too long and not too short. Cruise probably figured out scene that involve climbing and windy weather looks better with long hair.
Mission Impossible 5: Rogue Nation
Wait. he broke the hair pattern. Why?
Based on the trailer, here are FIVE hypothesis:
1. More motorcycle drifting.
2. Intense plane stunt.
3. Lots of wind involved.
4. Multiple jumping off the platform/building scenes.