You can see them even at that scale. The original experiments by Tyndall that demonstrated the effect were in a tube [1] currently on display at the Royal Institution.
Incorrect. This is a fundamental property of the molecule CO2. CO2 absorbs infrared radiation. In the atmosphere this property of CO2 prevents infrared radiation from radiating back out into space.
> While transparent to visible light, carbon dioxide is a greenhouse gas, absorbing and emitting infrared radiation ... Absorption of infrared light at the vibrational frequencies of atmospheric CO2 traps energy near the surface, warming the surface and the lower atmosphere. Less energy reaches the upper atmosphere, which is therefore cooler because of this absorption.
