Each of the phrases below shares a common quality. Can you determine what it is?

1. BAROMETRIC PRESSURE
2. COMPARISON SHOPPING
3. TIMBERLINE ELEVATION
4. PERIOD OF HIBERNATION

HINTS:
A. It has nothing to do with their meanings.
B. Each phrase conceals a related word.

Answer:

Hidden in each phrase is the name of a world capital:

1. baROMEtric pressure
2. comPARISon shopping
3. timBERLINe elevation
4. period of hiBERNation