Tropical cyclones over the Arabian Sea in the pre-monsoon season (May–June) have intensified since 1997 owing to significant reductions in storm-ambient vertical wind shear (VWS) in the troposphere; these reductions have decreased on average by about 3 m s−1 from the pre-1997 epoch (1979–1997) to the recent epoch (1998–2010)1. The authors attribute the reduction of pre-monsoon VWS to the dimming effects of increased anthropogenic black carbon and sulphate emissions.