We have long known of the heat retaining properties of carbon dioxide in the atmosphere.

This was proposed in the early 1800s by the French scientist Joseph Fourier (Van der Veen 2000), that the earth’s atmosphere retained some of the heat entering as sunlight, as happens in a glass greenhouse, that is, longwave radiation passes through the glass to the soil and surfaces within, which are heated, the heat is then emitted as shortwave radiation, infrared, which can’t pass through the glass as well.