Water vapor and temperature lapse rate feedbacks in the mid‐latitude seasonal cycle

The ongoing scientific debate regarding the role of water vapor feedback in climate change centers on the effects of water vapor vertical distribution and variation with climate change. The temperature lapse rate is another vertically dependent variable; its combination and interaction with water vapor feedback have an even greater potential for influencing the climate. Here we examine the vertical dependence of the feedbacks, as presently observed in the mid‐latitude seasonal cycle, by means of a radiative‐convective model with climatological lapse rates. It is found that both the water vapor and lapse rate feedbacks are positive, amplifying the seasonal surface temperature cycle by approximately 23% and 15%, respectively, and have considerable thermal coupling. The feedback contributions from the various vertical levels are essentially additive. These vertical contributions are characterized by a bimodal water vapor feedback, with upper and lower troposphere maxima, and by a predominant lapse rate feedback from the lower troposphere. Although a small negative water vapor feedback contribution is found at 150 mb, its significance is overshadowed by the strong positive feedbacks at all other levels, especially in the lower troposphere. The implications for climate change are discussed.