Warming alarmists claim: “Earth’s atmosphere acts like the glass in a greenhouse.”
This is false.
Glass is largely transparent to incoming solar radiation which warms whatever is inside the greenhouse. If the greenhouse had no walls (like the atmosphere), warmed greenhouse air would rise by convection, escape out via the open sides, and heavy cooler air near to the ground would flow in to take its place. This open “Greenhouse” would stay close to outside temperature.