Yes, negative numbers exist, and numbers beyond 100. But they’re not that important. 0 is basically the lowest temperature that matters in day to day life. If it’s colder, you don’t do anything different unless you’re preparing for an outdoor adventure. Same with 100. 100 is the hottest temperature that makes a difference. Beyond 100 it only matters if you’re preparing for an outdoor adventure. The 100 degree scale is about describing the normal range that humans interact with their environment in. Even if it can get extreme beyond that, that doesn’t mean the 0-100 scale isn’t useful.