Introduction

Abstract

Available observations indicate a global sea level rise during recent decades due to thermal expansion of the warming ocean and freshwater from melting continental ice1. Regional changes of sea level in the Indian Ocean (IO), which hosts lowland countries such as the Maldives, remain enigmatic because long-term observations are limited. How anthropogenic warming affects IO atmosphere-ocean circulation is unclear. Yet, regional estimates of future sea level rise are essential for effective risk assessment2. By combining in situ and satellite observations with model experiments, here we show a distinct spatial pattern of IO sea level change since the 1960s. Sea level has substantially decreased in the south tropical IO but increased elsewhere. This pattern is driven by changing surface wind associated with a combined enhancement of IO Hadley and Walker cells (atmospheric north-south and east-west overturning circulations, respectively), which is partly forced by the Indo-Pacific warm pool warming attributable to increasing greenhouse gases. Both the sea level and wind signals are robust to observational sampling and model differences. They imply that if ongoing anthropogenic warming dominates natural variability, this pattern is likely to persist and increase stress on the habitability and social structure of some coasts and islands.