How do greenhouse gases modify Earth's temperatures?

Answer 1

If you want to see an example of the greenhouse effect, just go to Venus! (Atmosphere of Venus: 96.5% carbon dioxide. Temperature of Venus: 467°C (872°F))

To answer your question, when rays of the sun come through our atmosphere they heat the land, water and such. This heat then radiates out from the warmed earth. Some of the goes back through the atmosphere and out into space, but the greenhouse gases capture and retain some of this heat. This is the natural greenhouse effect that keeps the planet warm. Any extra greenhouse gases (from man's activities of burning fossil fuels and deforestation) are too much for the natural carbon cycle to remove, so they absorb extra reflected heat. This is what is causing global warming.

Answer:

The popular view is that the atmosphere has some sort of layer of carbon dioxide "up there" that reflects heat back down to Earth rather than letting it escape to space. That would be like the glass on a greenhouse trapping warm air in while letting the sunlight through to increase the heat. In a greenhouse the sunlight warms the benches and floor, he warm objects heat the air, the air is trapped by the double layer of insulating glass.

It does not happen that way in our atmosphere.

Sunlight comes in and warms the Earth's surface. It warms the gases in the air too, at least some of them with a bond size that gets excited by sunlight. These special gases are greenhouse gases (carbon dioxide, methane, water vapour and a few others). They are mixed evenly through all of the atmosphere (not in layer). When the gases are warm they share their heat with all their gas molecule neighbour and heat the atmosphere generally.

The effect i more like wet sand in a microwave. Microwaves do not heat sand. They do heat water. When you microwave wet sand, the water heats up - might even turn to steam. The hot water warms the sand.