For example, we know that if the amount of carbon dioxide (CO2) in the Earth's atmosphere doubles from the pre-industrial level of 280 parts per million by volume (ppmv) to 560 ppmv, this will cause an energy imbalance by trapping more outgoing thermal radiation in the atmosphere, enough to directly warm the surface approximately 1.2 °C. (skepticalscience.com)
Since the solar input is being kept constant, the outgoing thermal radiation will have the same (constant) effective temperature, and the TAU = 1 level will continue to coincide with the same physical temperature equal to the effective temperature. (realclimate.org)
There is a graph showing the spectra of incoming solar radiation and outgoing thermal radiation. (desmogblog.com)