= Solution
The mechanisms affect surface energy input, heat supply from below, and the transport and thickness of <sea ice>. They reinforce one another: atmospheric warming and ocean heat thin the cover; circulation can export old ice; thinner ice melts earlier, increasing open-water absorption and strengthening <ice-albedo feedback>. Heat below the <cold halocline> matters only to the extent that mixing delivers it upward. Consequently the seven effects cannot be assigned independent percentages from the information given; their importance varies by region and year.
In a forward-looking answer from the paper's 2009 context, sustained warming would be expected to produce continued <Arctic sea ice decline>, a longer summer open-water season, less <multi-year sea ice>, and potentially nearly ice-free late summers within coming decades. Winter darkness permits new <first-year sea ice> to form, so loss of summer ice does not imply immediate year-round disappearance. Winter ice would tend to become thinner, more seasonal, and slower to recover after enhanced ocean heating. A precise date requires a forcing scenario and model, and internal variability causes year-to-year departures. https://onlinelibrary.wiley.com/doi/10.1029/2009GL037820/abstract[Wang and Overland's 2009 projection] is a contemporary example of such a conditional summer outlook.
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