We examine the midlatitude jet stream responses to projected Antarctic
and Arctic sea-ice loss and global ocean warming in coordinated
multi-model experiments from the Polar Amplification Model
Intercomparison Project. Antarctic and Arctic sea-ice loss cause an
equatorward shift of the winter jet stream in the southern and northern
hemisphere, respectively, on average across the models. Models with
stronger eddy feedback simulate farther equatorward jet shifts in
response to both Antarctic and Arctic sea-ice loss. The models simulate
too weak eddy feedback compared to the real world, particularly in the
northern hemisphere, resulting in an underestimation of the boreal jet
response to Arctic sea-ice loss. More precise estimates of the jet
shifts are obtained by using the observed eddy feedback as a constraint
and suggest that the equatorward jet shifts in response to Antarctic and
Arctic sea-ice loss exceed in magnitude the opposing poleward shifts due
to ocean warming.