Abstract. The mid-Piacenzian warm period (3.264 to 3.025 Ma) is the most
recent geological period with present-like atmospheric pCO2 and is thus expected to have exhibited a warm climate similar to or warmer
than the present day. On the basis of understanding that has been gathered on
the climate variability of this interval, a specific interglacial (Marine
Isotope Stage KM5c, MIS KM5c; 3.205 Ma) has been selected for the Pliocene
Model Intercomparison Project phase 2 (PlioMIP 2). We carried out a series
of experiments according to the design of PlioMIP2 with two versions of the
Institut Pierre Simon Laplace (IPSL) atmosphere–ocean coupled general circulation model (AOGCM): IPSL-CM5A
and IPSL-CM5A2. Compared to the PlioMIP 1 experiment, run with IPSL-CM5A, our
results show that the simulated MIS KM5c climate presents enhanced warming
in mid- to high latitudes, especially over oceanic regions. This warming can
be largely attributed to the enhanced Atlantic Meridional Overturning
Circulation caused by the high-latitude seaway changes. The sensitivity
experiments, conducted with IPSL-CM5A2, show that besides the increased
pCO2, both modified orography and reduced ice sheets contribute
substantially to mid- to high latitude warming in MIS KM5c. When considering
the pCO2 uncertainties (+/-50 ppmv) during the Pliocene, the
response of the modeled mean annual surface air temperature to changes to
pCO2 (+/-50 ppmv) is not symmetric, which is likely due to the
nonlinear response of the cryosphere (snow cover and sea ice extent). By
analyzing the Greenland Ice Sheet surface mass balance, we also demonstrate
its vulnerability under both MIS KM5c and modern warm climate.
The Structure and Predictability of the “High-Latitude Mode” in the CSIRO9 General Circulation Model
