It was 13 degrees, snow whirlpooling in 50-mile-an-hour gusts around us. Looking to Bill, I said brightly, shouting, really, so he could hear me under layers of fleece and wool, “All we need to do is stay warm!” I buckled the hip belt of my backpack. “Our only job is temperature regulation.”

“Yeah,” Bill shouted back. “I’ve been thinking about not freezing to death all morning.”