Meridional Heat Transport in the DeepMIP Eocene ensemble: non-CO2 and
CO2 effects
Abstract
The total meridional heat transport (MHT) is relatively stable across
different climates. Nevertheless, the strength of individual processes
contributing to the total transport are not stable. Here we investigate
the MHT and its main components especially in the atmosphere, in five
coupled climate model simulations from the Deep-Time Model
Intercomparison Project (DeepMIP). These simulations target the Early
Eocene Climatic Optimum (EECO), a geological time period with high CO2
concentrations, analogous to the upper range of end-of-century CO2
projections. Preindustrial and early Eocene simulations at a range of
CO2 levels (1x, 3x and 6x preindustrial values) are used to quantify the
MHT changes in response to both CO2 and non-CO2 related forcings. We
found that atmospheric poleward heat transport increases with CO2, while
the effect of non-CO2 boundary conditions (e.g., paleogeography, land
ice, vegetation) is causing more poleward atmospheric heat transport on
the Northern and less on the Southern Hemisphere. The changes in
paleogeography increase the heat transport via transient eddies at the
mid-latitudes in the Eocene. The Hadley cells have an asymmetric
response to both the CO2 and non-CO2 constraints. The poleward latent
heat transport of monsoon systems increases with rising CO2
concentrations, but this effect is offset by the Eocene topography. Our
results show that the changes in the monsoon systems’ latent heat
transport is a robust feature of CO2 warming, which is in line with the
currently observed precipitation increase of present day monsoon
systems.