the higher one climbs, the moreUses the pattern ~ば~ほど to express “the more..., the more...” or “the [comparative]..., the [comparative]....” Here, it means that as one climbs higher, it becomes increasingly cold or the temperature drops.
JA: 山は高く登れば登るほど、景色が美しくなる。
EN: The higher you climb the mountain, the more beautiful the view becomes.