Hothouse effect

[emmaareitch]

How does the heatwaves from the son enter the earth's atmosphere, reflects off the earth and is then unable to leave again? It gets thru' easily, so why can't it leave easily?

[rekstout]

When the heat energy (in the form energy waves in the IR spectrum) comes from the sun it is of a certain frequency - this frequency can pass through the atmosphere. When it is reflected off the ground, it changes frequency (just as some white light is absorbed by coloured objects thereby reflecting only certain light frequencies) these frequencies are less able to pass through the atmosphere on the way out.