Question

What would happen if most of Earth’s surface suddenly became covered with ice?

Answer 1

in other words "Earth would cool down because it would reflect more solar radiation."

Answer 2

There would be a lot less agricultural land available, so it would be very difficult to support the human population. And the physical shape of the continents would look completely different across the whole planet; A huge drop in sea level of up to 120 metres would close down marine channels and create new areas of land that could be used for habitation or agriculture.