Arctic warming under increased CO2 peaks in winter, but is influenced by
summer forcing via seasonal ocean heat storage. Yet changes in
atmospheric heat transport into the Arctic have mainly been investigated
in the annual mean or winter, with limited focus on other seasons. We
investigate the full seasonal cycle of poleward heat transport modelled
with increased CO2 or with individually applied Arctic sea-ice loss and
global sea-surface warming. We find that a winter reduction in dry heat
transport is driven by Arctic sea-ice loss and warming, while a summer
increase in moist heat transport is driven by sub-Arctic warming and
moistening. Intermodel spread in Arctic warming controls spread in
seasonal poleward heat transport. These seasonal changes and their
intermodel spread are well-captured by down-gradient diffusive heat
transport. While changes in moist and dry heat transport compensate in
the annual-mean, their opposite seasonality may support non-compensating
effects on Arctic warming.