The earth radiates the heat, and thus warms the air.
Reflection.
When a piece of bright tin is held near the fire, does the tin become hot?
No; the tin is scarcely warmed.
What does the tin do with the rays of heat from the fire?
The tin throws them back from its surface.
What is this called?
It is called Reflection of heat.
Do all substances reflect heat equally well?
No; some reflect much more heat than others.