When riding in cold weather, why is proper thermal windproof riding apparel critical for safety?

1. Wind chill rapidly induces hypothermia, causing severe shivering, numb fingers that cannot operate brake levers, and dangerously slowed mental reactions
2. Thick clothing is needed mainly to cushion the rider in a fall rather than to retain heat
3. Cold weather is only a concern on journeys longer than two hours
4. Shivering keeps the body warm, so cold poses no real risk to control of the machine