North Indian Ocean sea level rise in the past and future: The role of climate change and variability

Abstract

Sea-level rise is an inevitable consequence of climate change due to increased external forcings and potentially devastating effects on the coastal population, low-lying islands, and marine ecosystem. To better understand and quantify the impact of climate change and variability on the global and Indian Ocean sea level, we analyze observed, reanalysis, and climate model experiments from phase five and recent phase six of the Coupled Model Intercomparison Project (CMIP). Our analysis based on CMIP5 and CMIP6 models reveals that the global and North Indian Ocean (NIO) sea-level rise is primarily driven by anthropogenic forcing and internal variability likely to have a secondary contribution. Contrary to the global sea-level rise, mainly driven by mass contribution, the past NIO sea-level rise is dominated by the thermosteric contribution caused by the collaborative contribution of anthropogenic forcing and internal variability. The observed long-term trend in thermosteric sea level during 1955–2005 in the NIO is comparable to the global mean, while the projected sea-level rise is higher than the global mean. Since the thermosteric sea level dominates the past Indian Ocean sea level, it is crucial to investigate the future sea-level projection in the Indian Ocean under global warming. Notably, by the end of the 21st century, the most significant change in total sea level in the Indian Ocean is primarily in the Arabian Sea, with a rise of about 0.76 m in the NIO and 0.75 m in the global ocean based on high emission scenario (RCP 8.5) from CMIP5 simulation. Our study highlights the dominant contributors to the total sea-level rise and its projected rise over the 21st century in the densely populated Indian Ocean region, demanding better adaptation strategies and policymaking. © 2023 Elsevier B.V.