Hmm: If the planet warmed 11 degrees F, and if the Arctic averages -29F in winter now, can we safely conclude that there would be no Arctic sea ice in winter?

Model shows polar ice caps can recover from warmer climate-induced melting

A growing body of recent research indicates that, in Earth's warming climate, there is no "tipping point," or threshold warm temperature, beyond which polar sea ice cannot recover if temperatures come back down. New University of Washington research indicates that even if Earth warmed enough to melt all polar sea ice, the ice could recover if the planet cooled again.
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In the new research, scientists used one of two computer-generated global climate models that accurately reflect the rate of sea-ice loss under current climate conditions, a model so sensitive to warming that it projects the complete loss of September Arctic sea ice by the middle of this century.

However, the model takes several more centuries of warming to completely lose winter sea ice, and doing so required carbon dioxide levels to be gradually raised to a level nearly nine times greater than today. When the model's carbon dioxide levels then were gradually reduced, temperatures slowly came down and the sea ice eventually returned.

"We expected the sea ice to be completely gone in winter at four times the current level of carbon dioxide but we had to raise it by more than eight times," said Cecilia Bitz, a UW associate professor of atmospheric sciences.

"All that carbon dioxide made a very, very warm planet. It was about 6 degrees Celsius (11 degrees Fahrenheit) warmer than it is now, which caused the Arctic to be completely free of sea ice in winter."

NASA - Arctic Ice Meltdown Continues With Significantly Reduced Winter Ice Cover

As far as temperatures drop in the Arctic winter – on average to -34°C (-29°F) – a new study shows that in the last two years sea ice is shrinking on the surface of Arctic waters to record low levels.

All About Sea Ice

The freezing temperature of salt water is lower than fresh water; ocean temperatures must reach -1.8 degrees Celsius (28.8 degrees Fahrenheit) to freeze.