The effect of transient conditions on an equilibrium permafrost‐climate model

Equilibrium permafrost models assume a stationary temperature and snow‐cover climate. With a variable or changing climate, short‐term energy imbalances between the active layer and permafrost result in transient departures from the equilibrium condition. This study examines the effects of such variability on an equilibrium permafrost‐climate model, the temperature at the top of permafrost (TTOP) model. Comparisons between numerical results and temperatures predicted by the TTOP‐model suggest that stationary inter‐annual variability introduces an error in the top‐of‐permafrost temperature obtained with the equilibrium model that is higher where permafrost temperature is close to 0°C, although multi‐year averaging reduces the error to 0.1°C or less. In the presence of a warming trend, the equilibrium model prediction tracked the changing top‐of‐permafrost temperature until permafrost temperatures reached 0°C, after which the equilibrium model produced significant errors. Errors up to 1°C were due to the temperature gradient through the developing talik, and depended on the warming rate, and the thickness of the talik. For all warming rates, the error was largest when the permafrost table was about 4 m below the surface, with the error declining as the permafrost table fell. Copyright © 2007 John Wiley & Sons, Ltd.