Abrupt monsoon transitions as seen in paleorecords can be explained by moisture-advection feedback.

Abrupt Monsoon Transitions Exist in Paleorecords and Pertinent Models Paleoclimatic records show abrupt monsoon shifts at various different locations and historic periods (1–5). An important question is whether such transitions are possible in the future (6). To this end, we carved out the physical mechanism for such transitions in a purposefully simple conceptual model (7). Recently, Boos and Storelvmo (8) claimed that introducing adiabatic cooling into our model (7) eliminates these abrupt transitions. This claim is not generally true. As can be seen from their figure 1, Boos and Storelvmo (8) only eliminate abrupt transitions if most of the energy from the rain’s latent heat release is consumed by adiabatic cooling. Although adiabatic cooling exists and is, as shown below, implicitly accounted for in ref. 7, it is not a valid assumption that most of the latent heat release is consumed by this process. By contrast, monsoon circulation is predominantly sustained by latent heat release, as shown in a number of studies (e.g., ref. 9) including figure 2 in ref. 7.