Above treeline in New Hampshire brings a slew of new elements- blinding cold, brutal winds, deep fog, and ice- lots and lots of ice.
On Mount Washington, one of the state's largest mountains, it's currently -33 degrees F. That's painful cold. That's cold that requires double thick, extra windproof mitts, a solid face mask, ski goggles that don't fog up. That's cold enough to whiten any exposed skin within seconds.
Sometimes it gets so cold that it hurts to breath. Your nose doesn't run anymore, because- well- you can figure out why. Oh and stopping to go the bathroom? Just forget about that until your are back down at your car.
One recent sub-temperature treeline hike here.