Geophys. Res. Lett. (2019).

In response to warming, Earth system models project an increase in South Asian monsoon (SAM) rainfall and intensity, while observations depict a decrease since the 1950s. Reconciling this discrepancy has proven difficult, owing to uncertainty in regional precipitation records and aerosol impacts.

Sean Bryan, from Colorado State University, United States, and colleagues used Red Sea corals along the Saudi Arabian coast to reconstruct a proxy for SAM intensity over the past 250 years. They did this by measuring annual barium/calcium ratios (Ba/Ca), which reflect dust deposition into the Red Sea. Broader SAM circulation is associated with winds that blow dust from the Sudanese desert east over the Red Sea, and corals incorporate dissolved barium. The authors found an increase in Ba/Ca, which suggests an increase in SAM intensity, over the past 250 years. They attribute this increase to northern hemisphere warming, though they note a decrease in multidecadal variability in the latter half of the record. These results fit with the understanding that monsoons will generally strengthen in a warming climate.