Abstract
AbstractPrevious work demonstrated a significant correlation between tropical surface air temperature and equilibrium climate sensitivity (ECS) in PMIP (Paleoclimate Modelling Intercomparison Project) phase 2 model simulations of the last glacial maximum (LGM). This implies that reconstructed LGM cooling in this region could provide information about the climate system ECS value. We analyze results from new simulations of the LGM performed as part of Coupled Model Intercomparison Project (CMIP5) and PMIP phase 3. These results show no consistent relationship between the LGM tropical cooling and ECS. A radiative forcing and feedback analysis shows that a number of factors are responsible for this decoupling, some of which are related to vegetation and aerosol feedbacks. While several of the processes identified are LGM specific and do not impact on elevated CO2 simulations, this analysis demonstrates one area where the newer CMIP5 models behave in a qualitatively different manner compared with the older ensemble. The results imply that so‐called Earth System components such as vegetation and aerosols can have a significant impact on the climate response in LGM simulations, and this should be taken into account in future analyses.
Highlights
The last glacial maximum (LGM) is defined as the period during the last glacial-interglacial cycle when ice sheet volume was at a maximum [e.g., Mix et al, 2001], from 23 to 19 kyr B.P
The PMIP2 equilibrium climate sensitivity (ECS) values derived from the Gregory analysis strengthens the negative correlation between climate sensitivity and the lgm-piControl tropical temperature change for each model, changing from −0.75 to −0.79
A similar analysis for the abrupt4×CO2 simulations with these same models conducted as part of CMIP5 shows a strong relationship between ECS and tropical warming, and this is shown in the supporting information Figure S1
Summary
The last glacial maximum (LGM) is defined as the period during the last glacial-interglacial cycle when ice sheet volume was at a maximum [e.g., Mix et al, 2001], from 23 to 19 kyr B.P. (before present). This period has been a focus of paleoclimate study for several decades, because it constitutes an example of a near-equilibrium global climate state which is very different from today’s. The climate of the LGM is characterized by large ice sheets which dominated the Northern Hemisphere (e.g., as reconstructed by Peltier [2004]) and by a significant reduction in the concentration of the natural greenhouse gases (GHG) compared to the preindustrial [Petit et al, 1999; Spahni et al, 2005]. The radiative forcing from these ice sheets and reduced GHG levels is estimated to be approximately equal in magnitude to that from a quadrupling of CO2, making the LGM one candidate time period for studying well-resolved large-scale change in the global environment [Braconnot et al, 2012]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
