Air temperature decreasing with height in the troposphere due to adiabatic expansion and radiative balance is a fundamental physical principle of atmospheric science that does not require citation.
The claim describes a textbook physical phenomenon of atmospheric science (the tropospheric lapse rate, driven by adiabatic processes and radiative-convective equilibrium). This is a well-established, foundational fact of everyday scientific observation and physical definition rather than a disputed empirical hypothesis needing new evidence.