  Freshwater forcing from a retreating Antarctic Ice Sheet could have a wide
range of impacts on future global climate. Here, we report on multi-century
(present-2250) climate simulations performed using a fully coupled numerical
model integrated under future greenhouse gas emissions scenarios IPCC RCP4.5
and 8.5, with meltwater discharge provided by a dynamic-thermodynamic ice sheet
model. Accounting for Antarctica's meltwater contribution raises sub-surface
ocean temperatures by 1 C at the ice margin, beyond rates currently projected.
In contrast, 2-10 C cooler surface air and ocean temperatures in the Southern
Ocean cause sea ice to expand and delay the increase of projected global mean
anthropogenic warming. In addition, the projected loss of Arctic winter sea ice
and weakening of the Atlantic Meridional Overturning Circulation are delayed be
several decades. Our results demonstrate a clear need to more accurately
account for meltwater input from ice sheets if we are to make confident climate
predictions.
