Why is the greenhouse effect only one way?

Question

So what I’m reading is that these gas absorb the light from the sun and keeps it trapped on the earth.

What I don’t get is how is it letting the light and heat in from the sun in, but not the light and heat reflected from the Earth out? If it’s a barrier, shouldn’t it block both ways? If it’s not a barrier, how is it trapping the heat?

In: 950

Answer 1

So the thing about greenhouse gasses is that they are transparent to visible light but opaque to infrared radiation.

So light from the sun passes through the atmosphere. The energy is absorbed by things on the planet’s surface. Those things then release that energy through blackbody radiation, which will be in the infrared range, which we experience as heat.

That radiation ideally reaches space and beyond, cooling the planet. But greenhouse gasses reflect it back to the earth’s surface instead.

It’s exactly like a literal greenhouse, except with gas instead of glass.