@pschwede Oh the experiment is simple. You either put a hot objects ot an object you shine light on, inside a clear tank filled with a gas, then stick that ina . larger tank under vacuum.

You then observe to see how long it takes the hot object to reach room temperature (or some fixed point). You repeat this with a GH gas int eh chamber then do it again with a non-GH gas. It can be trivially observed that with a GH gas present the object retains its heat significantly longer.