Quote:

The loss of Arctic sea ice is a conspicuous example of climate change. Climate models project ice-free conditions during summer this century under realistic emission scenarios, reflecting the increase in seasonality in ice cover. To quantify the increased seasonality in the Arctic-Subarctic sea ice system, we define a non-dimensional seasonality number for sea ice extent, area, and volume from satellite data and realistic coupled climate models. We show that the Arctic-Subarctic, i.e. the northern hemisphere, sea ice now exhibits similar levels of seasonality to the Antarctic, which is in a seasonal regime without significant change since satellite observations began in 1979. Realistic climate models suggest that this transition to the seasonal regime is being accompanied by a maximum in Arctic amplification, which is the faster warming of Arctic latitudes compared to the global mean, in the 2010s. The strong link points to a peak in sea-ice-related feedbacks that occurs long before the Arctic becomes ice-free in summer.

https://www.nature.com/articles/s41598-017-04573-0

Models all the way down.  But hey they are "realistic" models. ::)

CMIP5 and RCP8.5. What's not to like? ;D ;D ;D ;D ;D ;D

https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs41598-017-04573-0/MediaObjects/41598_2017_4573_Fig1_HTML.jpg