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.

A central paradox of the global monsoon record involves reported decreases in rainfall over land during an era in which the global hydrologic cycle is both expected and observed to intensify. It is within this context that this work develops a physical basis for both interpreting the observed record and anticipating changes in the monsoons in a warming climate while bolstering the concept of the global monsoon in the context of shared feedbacks. The global-land monsoon record across multiple reanalyses is first assessed.

South of Africa, the Agulhas ocean current system transports warm, salty water from the Indian Ocean to the Atlantic Ocean. This study shows that the mesoscale variability of the Agulhas system has intensified over recent decades, apparently owing to enhanced trade winds over the tropical Indian Ocean.

More than one billion people live in regions affected by the South Asian summer monsoon. This Review provides an overview of our understanding of summer monsoon rainfall variability and its causes, and considers how the monsoon will change as a consequence of global warming.

South of Africa, the Agulhas Current retroflects and a portion of its waters flows into the South Atlantic Ocean, typically in the form of Agulhas rings. This flux of warm and salty water from the Indian to the Atlantic Ocean (the Agulhas leakage) is now recognized as a key element in global climate. An Agulhas leakage shutdown has been associated with extreme glacial periods, whereas a vigorous increase has preceded shifts towards interglacials.