Schwarzschild formulated in 1906 a mathematical model for radiative heat transfer based on two-way flow of heat energy, which allowed simple analytical solution and thus become popular. Schwarzschild’s model has been used to give support to an idea of “back radiation” with heat transfer from cold to warm as an element of a “greenhouse effect” threatening humanity by global warming from burning of fossil fuel adding CO2 to the atmosphere.

However, Schwarzschild’s model including “back radiation” is unphysical, which questions the existence of a “greenhouse effect” and thus also CO2 alarmism. The unhysical aspect of Schwarzschild’s model is exposed here.