Sea Level Trends in Southeast Asian Seas

The Southeast Asian sea regional sea level trends are some of the highest observed in the modern satellite altimeter record that now spans two decades. By examining the historic sea level record, we find that decadal-scale sea level trends over the past 110 years exhibit good agreement with climate variability associated with the Pacific Decadal Oscillation and related fluctuations of trade winds in the region. Associated with this variability, the region exhibits sea level trends that vary dramatically over the time period from 1900 to present. This historical variation coupled with current conditions in the Pacific Ocean suggests that the strong regional sea level trends observed during the modern satellite altimeter record will abate as trade winds fluctuate on decadal and longer timescales. Furthermore, after removing the contribution of the Pacific Decadal Oscillation to sea level trends in the past 20 years, the rate of sea level rise is greatly reduced in some parts of the region, while remaining high in other areas. On the one hand, as a result of the influence of the PDO, the sea level trends in some part of the region during the 2010s and 2020s are likely to be less than the global mean sea level (GMSL). On the other hand, this result also suggests the presence of an anthropogenic sea level signature in the western tropical Pacific with associated trends persisting into the future. As this region is particularly at threat to rising sea levels given the extent of coastline and low-lying land, improving our understanding of sea level trends in the past, present and future is essential to planning, mitigation and adaptation efforts.