Picture (above): Monsoon rain in Bharat, India. Credit: Pratik Gaikwad (Pixabay).

Comparing past and future changes in Southern Hemisphere monsoons can provide insights into the different factors influencing them. In this study, monsoonal changes under a high emissions future scenario were compared with changes in the mid-Holocene (6000 years before present) using a set of climate model simulations.

The researchers found Southern Hemisphere monsoons all weakened in the mid-Holocene simulations due to dynamic factors linked to changes in the seasonal cycle of incoming solar radiation.

In simulations of the future under a business-as-usual scenario, Southern Hemisphere monsoons generally strengthened and expanded due to thermodynamic factors. Differences in heating contrasts between land and ocean were also important, and these were linked to changes in the Walker and Hadley circulations.

Paper: D’Agostino, R., J. R. Brown, A. Moise, H. Nguyen, P. L. Silva Dias, and J. Jungclaus, Contrasting Southern Hemisphere monsoon response: mid-Holocene orbital forcing versus future greenhouse-gas induced global warming. J. Climate, doi: https://doi.org/10.1175/JCLI-D-19-0672.1.