The Arctic lapse rate feedback: An energy budget analysis of CMIP6 models

The strong warming trend in the Arctic is mostly confined at the surface, and particularly evident during the cold season. The lapse rate feedback (LRF) stands out as one of the dominant causes of the Arctic amplification (besides the surface albedo feedback) given its differing response between high and lower latitudes. The LRF is the deviation from the uniform temperature change throughout the troposphere, and can thereby be quantified as the difference of tropospheric warming and surface warming. In the Arctic, it enforces a positive radiative feedback as the bottom-heavy warming is increasingly muted at higher altitudes, which has been suggested to relate to the lack of vertical mixing. In fact, climate model studies have recently identified more negative lapse rates for models with stronger inversions over large parts of the Arctic ocean, and snow-free land during winter.

Here we quantify individual components of the atmospheric energy balance to better understand the determination of the temperature lapse rate in the Arctic, which does not only interact with the surface albedo feedback, but also changes in atmospheric transport. A decomposition of the atmospheric energy budget is derived from the 6th phase of the Coupled Model Intercomparison Project (CMIP6), and concerns the radiation budgets, the transport divergence of heat and moisture, and the surface turbulent heat fluxes. Alterations of the budget components are obtained through pairs of model scenarios to simulate the impact of increasing atmospheric CO2 levels in an idealized setup.

The most notable features are the strongly opposing winter changes of the surface heat fluxes over regions of sea ice retreat and open Arctic ocean, and the interplay with the compensating energy transport divergence which can be linked to the near-surface air moist static energy in an energetic-diffusive perspective. We further aim to relate the changes of individual energetics to the temperature lapse rate in the Arctic to better understand and quantify the factors contributing to its evolution.