On cold days, earmuffs are necessary.

She was wearing earmuffs to protect her ears from the cold.

You need earmuffs on cold days.

Your cooperation is needed for this project.

I need you.

On cold days, warm coffee is the best.

On a cold winter night, hot cocoa is the best.

The cold has become severe.

It's very cold today, isn't it?

It's difficult to go outside in this coldness.