As a high school student I once performed an experiment where I had a sealed glass aquarium, the bottom of which was covered with soil. Inside this aquarium I had a chemical reaction to produce CO2, after which I would shine a lamp above the aquarium (outside the sealed part) and would measure the temperature while the air inside the aquarium heated.
Initially, I expected temperatures to rise faster/higher with more CO2 in the aquarium, but I found the opposite.
Check mate.
While that obviously was a failed experiment for several reasons and does not disprove the link between CO2 and climate change at all, I do wonder how global warming (planar warming?) does not fit into FET?