Lecture 1 of the
ICTP/UniTN/UniAQ Joint International Seminar Series
on Weather and Climate: From Fundamentals to Applications
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Since the 1970s, simulations of climate change forced by increased CO2 concentrations have predicted warming that is greatest in polar regions. This polar-amplified warming has been variously attributed to the ice-albedo feedback, associated with the retreat of reflective sea ice in summer; the lapse rate feedback, associated with vertically nonuniform atmospheric warming in winter; and changes in energy transport by atmospheric circulations. Uncertainty in projections of Arctic climate change arise in part from incomplete understanding of the interconnected nature of these processes. Here, I present a new implementation of an idealized model to systematically investigate the roles of moist energy transport and sea ice in driving polar amplification. I additionally introduce a diagnostic decomposition of the lapse rate feedback, applied to an ensemble of comprehensive models, that isolates influences from dynamically distinct atmospheric regions. These analyses reveal the importance of ice thermodynamics and how the lapse-rate and sea-ice albedo feedback together dominate Arctic amplification as a coupled ocean-atmosphere mechanism operating across the seasonal cycle.