The greenhouse effect is not unclear; it is a simple, demonstrable fact of nature.
If you wrap a blanket around yourself, it is not the blanket that warms you with it's own energy by convection. The blanket is preventing the emission of heat away from your body. That is a thermal imbalance. So your body warms until the energy is again in balance.
A greenhouse gas does the same thing, it prevents radiation from escaping to space.
You can see how various gases affect the transmission of radiation through our climate system:
If you want to test the theory more sensibly, one should expect cloudy nights to be warmer than clear nights. This has been tested, and indeed cloudy nights are warmer than clear nights.