Greenhouse gases primarily warm the planet by absorbing incoming short-wavelength solar radiation in the stratosphere, which directly increases the thermal energy of the troposphere through convection.

Homonuclear diatomic molecules like $N_2$ and $O_2$ do not contribute to the greenhouse effect because their vibrations do not create a change in molecular dipole moment, rendering them infrared-inactive.

Increasing the concentration of greenhouse gases reduces the planetary albedo, allowing more solar radiation to reach the surface and thus raising the global average temperature.

Triatomic molecules like $C{O}_2$ are highly effective greenhouse gases because they possess a large permanent dipole moment in their linear ground state, allowing them to scatter incoming infrared light.