<p><strong>Abstract.</strong> The recent Arctic sea-ice reduction is associated with an increase in the ice-free season duration, with comparable contributions of earlier retreat and later freeze-up. Here we show that within the next decades, the trends towards later freeze-up should progressively exceed and ultimately double the trend towards an earlier ice retreat date. This feature is robustly found in a hierarchy of climate models and is consistent with a simple mechanism: solar energy is

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... sorbed more efficiently than it can be released in non-solar form until freeze-up. Based on climate change simulations, we envision an increase and a shift of the ice-free season towards fall, which will affect Arctic ecosystems and navigation.</p>