system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't greenhouse gases reflect just as much incoming sunlight as they trap?

The common explanation of greenhouse gases is that sunlight that would bounce off the Earth out into space instead bounces off the greenhouse gas, trapping that heat on Earth. 

But if greenhouse gases simply reflect solar radiation, wouldn't they also reflect from the "outside", too, thus preventing solar radiation from reaching the Earth in the first place?
gpt
Greenhouse gasses, like the glass of their namesake, are transparent to most of the visible light spectrum, but more absorbent of infrared light (ie heat radiation). 

When visible light passes through the atmosphere and hits the earth, it warms up the earth, which then re-radiates that energy to space as infrared. 

So hence the greenhouse gasses pass through the visible light on the way down, but block the infrared from getting back out again, so energy is trapped in the atmosphere.