[expat2]

1. The reason a (real) greenhouse warms up is because vertical convection (which causes the land outside the greenhouse to cool off) is blocked by the glass roof. Similarly, the biggest cause of warming of the Earth is the tropopause, which also blocks vertical convection.
2. While CO2 does have the potential to provide some blocking of IR, its role is diminished by the presence of other mechanisms which allow heat to circumvent the CO2 effect in most of the troposphere: (a) vertical convection, (b) latent heat of water (water vapor changes to liquid water droplets and then changes to ice particles, each time circumventing the CO2 affect by transferring heat to higher altitudes.(c) most of the heat input to earth is in the tropics and thunderstorms in the tropics are very common: warm moist air rises to the upper levels of the troposphere, cools to ice pellets which fall to the lower levels as cold rain, thus again circumventing any CO2 effect.
3. There is considerable emphasis on IR absorption by CO2, even though it is largely circumvented in the lower and middle troposphere, but CO2 also plays an emissive, cooling role, which is very important at the upper troposphere, where other means of transferring energy across the stratosphere are no longer available (water is largely frozen out by the extreme cold, and convection is blocked by the stratosphere.

[TigersEye]

I have heard that.

Sky-high hole blown in AGW theory?

"Forbes reports on a peer-reviewed study that uses NASA data to show that the effects of carbon-based warming have been significantly exaggerated. In fact, much of the heat goes out into space rather than stay trapped in the atmosphere, an outcome that started long before AGW alarmists predicted:"

Falsification Of The Atmospheric CO2 Greenhouse Effects Within The Frame Of Physics