The concept of feedback is key in assessing whether a perturbation to a system is amplified or damped by mechanisms internal to the system. In polar regions, climate dynamics are controlled by both radiative and non-radiative interactions between the atmosphere, ocean, sea ice, ice sheets and land surfaces. Precisely quantifying polar feedbacks is required for a process-oriented evaluation of climate models, a clear understanding of the processes responsible for polar climate changes, and a reduction in uncertainty associated with model projections. This quantification can be performed using a simple and consistent approach that is valid for a wide range of feedbacks, offering the opportunity for more systematic feedback analyses and a better understanding of polar climate changes.

This work was supported by FNRS (Grant agreement no. T.0007.14), the PRIMAVERA EU-H2020 project (Grant agreement no. 641727), the Ministerio de Economía, Indistria y Competitividad (MINECO) and Belgian Science Policy Office. K.C. Armour was supported by National Science Foundation award OCE-1523641. H. Goosse is the Research Director within the Fonds National de la Recherche Scientifique (F.R.S.-FNRSBelgium). François Massonnet is a F.R.S-FNRS Post-Doctoral Researcher. Jennifer Kay's efforts were supported by NASA 15-CCST15-0025. A. Bodas-Salcedo was supported by the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101). P. Kushner acknowledges the support of the Natural Sciences and Engineering Research Council of Canada's Canadian Sea Ice and Snow Evolution Network (see www.CanSISE.ca). This paper is the outcome of a workshop held in May 2016 at the Université catholique de Louvain, Belgium in the framework of the Polar Climate Prediction Initiative supported by the World Climate Research Programme.

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