In that case, CO2 should have an overall negative effect on temperature, by emitting proportionally more IR upwards than it receives from that direction.
"There's more infrared coming from below than above."
"In that case, CO2 should have an overall negative effect on temperature, by emitting proportionally more IR upwards than it receives from that direction."
When an individual CO2 molecule absorbs a photon it can emit one in any direction. But the aggregate of an entire layer of CO2 in the atmosphere doesn't have that behavior.
A CO2 molecule at the bottom of the layer will emit a photon in a random direction. If it emits downwards then there's no CO2 to interact. But if it goes up it can hit another CO2 molecule, which will in turn emit it back in a random direction, which might be back downwards again.
This is a very simplified picture of course, but it illustrates the point. A CO2 layer in the atmosphere isn't like a single CO2 molecule. It's like a thin insulating blanket that has a slight tendency to reflect more infrared back.
That doesn't mean AGW is valid of course. It takes more than this. Some of the reasons I'm still skeptical of AGW are:
CO2 is a relatively minor greenhouse gas in our atmosphere. So say we double the amount of CO2. If CO2 makes up only 2% of greenhouse effect then we've only increased the effect by 2%.
We are talking about relatively minor changes in temperature over long periods of time. But we don't have reliable long term temperature records. Even recent ones made by recording devices are subject to other effects that have to be estimated and corrected. Long term records have to be constructed by indirect means. That's all fine, but every correction factor and every layer of indirection introduces a margin of error. I'm not convinced that the changes being discussed are larger than the margin of error in the measurements.
The global climate may include self-regulating mechanisms. For example, an increase in temperature may increase cloud cover, reflecting more heat outwards. Or an increase in CO2 may cause greater plant growth. Effects like that would act as regulators.
Even if we accept that temperature has risen, the evidence for a human cause seems to be entirely an argument of, correlation equals causation, which is probably the single most common logical fallacy encountered in science. And the correlation isn't that great anyway. We know global climate was getting warmer coming out of the Little Ice Age so how can we distinguish that natural trend from human effects?
None of that disproves AGW, but they are reasons I don't think we should be confident in it.