Variation in the spectrum due to an upper atmosphere temperature perturbation, centred at 10⁻⁴ bar. Due to the changes in the temperature structure, both the equilibrium chemical abundances and the opacities structure change, inducing changes in the outgoing emitted spectrum. The largest impact of this upper atmosphere warming is on the 3.3 µm absorption feature, due to its relatively high abundance in the upper atmosphere and large cross section at 3.3 µm, which causes the atmosphere to become optically thick at lower pressures.