see a lay explanation of this paper here and here. Following publication, Smith published a rebuttal, and then a rebuttal of Smiths paper was published! See also here.
another scientific post called "The Climate Catastrophe- A Spectroscopic Artifact? by Dr. Heinz Hug argues that "laboratory measurements of the infrared absorption of carbon dioxide using an FT-IR spectrometre suggest that the radiative forcing for CO2 doubling must be much less than assumed by climate scientists until now. A reduction factor of 80 is likely." See also here. And here.