An ongoing shift in Pacific Ocean sea level

Abstract

Based on the satellite altimeter data, sea level off the west coast of the United States has increased over the past 5 years, while sea level in the western tropical Pacific has declined. Understanding whether this is a short‐term shift or the beginning of a longer‐term change in sea level has important implications for coastal planning efforts in the coming decades. Here, we identify and quantify the recent shift in Pacific Ocean sea level, and also seek to describe the variability in a manner consistent with recent descriptions of El Nino‐Southern Oscillation (ENSO) and particularly the Pacific Decadal Oscillation (PDO). More specifically, we extract two dominant modes of sea level variability, one related to the biennial oscillation associated with ENSO and the other representative of lower‐frequency variability with a strong signal in the northern Pacific. We rely on cyclostationary empirical orthogonal function (CSEOF) analysis along with sea level reconstructions to describe these modes and provide historical context for the recent sea level changes observed in the Pacific. As a result, we find that a shift in sea level has occurred in the Pacific Ocean over the past few years that will likely persist in the coming years, leading to substantially higher sea level off the west coast of the United States and lower sea level in the western tropical Pacific.

The Dominant Global Modes of Recent Internal Sea Level Variability

“…This mode represents a biennial oscillation in ENSO, specifically the case when there is a year‐to‐year shift between the phases of ENSO. As described in Hamlington et al (), this type of shift was particularly visible when the 1997/1998 El Niño was followed by a strong La Niña. During the record considered here, the 2009/2010 El Niño followed by the previously discussed La Niña is the most prominent occurrence of this type of variability, although a weaker phase transition over the period from 2012 to 2014 is also featured.…”

“…While not specifically relying on comparisons to climate indices, the general approach taken here does not preclude links or attribution to well‐known climate signals like ENSO or the PDO. Among the questions we seek to answer or provide additional insight into are as follows: What are the dominant signals or modes characterizing sea level change on intraseasonal to decadal timescales? To what extent does internal variability obscure the background trend in satellite records, both regionally and globally? What contributes to the short‐term rise and fall of global mean sea level? What role does variability in the water cycle play in changes in sea level, particularly on global scales? Are satellite records of terrestrial water storage now long enough to extract long‐term trends regionally and globally? These questions have been the focus of a number of recent papers that have resulted in important insights into the role of intraseasonal to decadal variability in sea level (e.g., Boening et al, ; Cazenave et al, ; Fasullo et al, ; Fasullo & Nerem, ; Hamlington et al, , , , ; Reager et al, ; Zhang & Church, ). This study differs primarily by not targeting a particular climate signal a priori and instead simultaneously looking for dominant modes that are shared across data sets.…”

Contributions of Greenland and Antarctica to Global and Regional Sea Level Change

“…It remains to be determined if this reflects errors in the data (e.g., Watson et al, 2015) or natural decadal variability. Satellite altimetry also provides estimates of the spatial variation of sea level rise over the same time period (Figure 2), although this map tends to be more influenced by decadal variability (Hamlington et al, 2016).…”

Storm surge along the Pacific coast of North America

“…However, a recent study by Hamlington et al . [] indicates that North Pacific eastern boundary sea levels are now rising, affirming the anticipated resumption of RSL rise by Bromirski et al . [].…”