Are the interglacial epochs analogue of the Asian-African monsoon response to global warming?

Abstract

Abstract Precipitation was claimed to increase over Asian and North African monsoon (AAM) regions during past interglacial epochs and also under future global warming scenarios. Using CMIP6 model experiments, this study compares the changes of AAM in interglacial epochs to global warming. Moisture budget analysis shows that the increased monsoon rainfall during interglacial epochs primarily results from the dynamic process associated with strengthened monsoon circulation, but is caused by thermodynamic process under global warming associated with increased mean moisture. To disentangle the mechanism for the distinct changes in vertical and horizontal monsoon circulation, we further decompose the response of AAM to global warming into the direct effect from CO2 radiative forcing and the indirect effect due to increased sea surface temperature (SST), based on idealized CMIP6 experiments. The results show that the effect of direct CO2 radiative forcing on the AAM is an analogue to that in interglacial epochs driven by enhanced land-ocean equivalent potential temperature contrast, both of which are characterized by strengthened vertical and horizontal monsoon circulation despite regional difference. However, the above effect is overwhelmed by the substantially increased SST under global warming, which is absent during interglacial epochs. The substantial SST warming acts to weaken the monsoon circulation by decreasing the land-ocean equivalent potential temperature contrast and enhancing the atmospheric static stability. Our results demonstrate that the interglacial epoch is not an analogue of the AAM response to global warming, and the lack of global SST warming is responsible for their difference.