Heat and freshwater changes in the Indian Ocean region

Across the Indo-Pacific region, rapid increases in surface temperatures, ocean heat content and concomitant hydrological changes have implications for sea level rise, ocean circulation and regional freshwater availability. In this Review, we synthesize evidence from multiple data sources to elucidate whether the observed heat and freshwater changes in the Indian Ocean represent an intensification of the hydrological cycle, as expected in a warming world. At the basin scale, twentieth century warming trends can be unequivocally attributed to human-induced climate change. Changes since 1980, however, appear dominated by multi-decadal variability associated with the Interdecadal Pacific oscillation, manifested as shifts in the Walker circulation and a corresponding reorganization of the Indo-Pacific heat and freshwater balance. Such variability, coupled with regional-scale trends, a short observational record and climate model uncertainties, makes it difficult to assess whether contemporary changes represent an anthropogenically forced transformation of the hydrological cycle. Future work must, therefore, focus on maintaining and expanding observing systems of remotely sensed and in situ observations, as well as extending and integrating coral proxy networks. Improved climate model simulations of the Maritime Continent region and its intricate exchange between the Pacific and Indian oceans are further necessary to quantify and attribute Indo-Pacific hydrological changes. The Indian Ocean has undergone substantial heat and freshwater changes. This Review uses various data sources to examine the causes of contemporary and longer-term hydrological changes, revealing that trends over the twentieth century are linked to anthropogenic forcing, but that those since 1980 are related to the Interdecadal Pacific oscillation.

Automated summary

This article summarizes the heat and freshwater changes in the Indian- Pacific region, indicating that the changes in the 20th century are related to anthropogenic factors, while those since 1980 are related to multi-decadal variability, making it difficult to determine whether contemporary changes represent a human-induced transformation of the hydrological cycle.