Revisiting the Apparent Negativity of Lapse-Rate Feedback Through a Physics-Based Climate Feedback Framework

In this study, we revisit the widely accepted interpretation of predominantly negative lapse-rate feedback, particularly in the tropics, by applying a physics-based climate feedback framework. We perform a side-by-side comparison of TOA-based PRP (partial radiative perturbation) and EGK-centered (energy gain kernel) climate feedback analysis frameworks. The only difference between them lies in their approach to accounting for temperature feedback. Under the EGK framework, all input energy perturbations are intimately related to temperature feedback through energy amplification following a multiplication role. The vertically integrated amplified input energy perturbation by temperature feedback is always substantially greater than the vertically integrated input energy itself. Such great amplification arises from the continuous back-and-forth relay of warming-induced thermal emissions from individual layers to absorption by other layers throughout the atmosphere-surface column until the system reaches a new equilibrium state. This is the positive aspect of temperature feedback. Temperature changes predicted from EGK automatically ensures energy is balance at all layers, including the TOA, through their thermal emissions. Thermal emissions reflect the negative aspect of temperature feedback.

The perturbation energy balance equation at the TOA only involves a simple addition of vertically integrated (partial) energy perturbations associated with external forcing and non-temperature feedbacks, plus OLR perturbations due to temperature feedback. The lapse-rate feedback mainly reflects the level where input energy is placed, rather than the physical nature of air temperature feedback. Its sign changes from positive for input energy at lower levels to negative for input energy at upper levels. Because energy perturbations due to radiative processes tend to have vertically decreasing profiles, their lapse-rate feedback tends to be predominantly positive. When also considering non-radiative feedbacks, such as enhanced vertical convection, the net effect of non-temperature feedbacks tends to be weak or even negative at the surface but strongly positive in the upper atmosphere in the tropics. This explains why the lapse-rate feedback is predominantly negative in the tropics.