You need to adjust your clothes to match the terrain. On climbs I take off a vest and unzip my jersey(s). If it's warm enough I use arm warmers, so I can slide them down when on climbs. If I have a long sleeved base layer I will push the sleeves up so I can ditch some heat from my arms.

The idea is to disrobe enough so that you're not getting drenched in sweat on the climb. Then at the top you zip up, pull up arm warmers, put on the vest, etc for the descent.