The Climate CIRCulator is a monthly newsletter covering climate science and the Northwest written by scientists and communicators.
Previous attempts to quantify the impacts of climate change on coastal areas have focused largely on the impacts of sea level rise, and while mean sea level rise will undeniably impact coastal areas, a recent study suggests we should not overlook other important climatic processes as well.
The study, published in Nature Geoscience, was led by Patrick Barnard and includes a long list of contributors, among them CIRC researcher Peter Ruggiero, whose work has focused on preparing Northwest residents for coastal hazards.
In their research, Barnard and colleagues have spread their net wide, spanning six locations throughout the Pacific Ocean basin, from Australia to the U.S. West Coast. The data the researchers were interested in tracking revolved around four important climate indices: the Pacific Decadal Oscillation; the Multivariate El Niño Southern Oscillation Index, which includes both El Niño and La Niña; the Southern Annular Mode; and the Pacific North American Pattern.
When used together, the researchers conclude, the state of these indices can be used as a tool to project when major impacts on coastal communities may occur, impacts that can range from flooding to erosion, and may be experienced (and here is the important part) regardless of mean sea level rise. Not surprisingly, the researchers observe, the impacts varied by climate index and by location.
While the climate indices provide useful information as to the potential for coastal impacts, as far as actual impacts to coastal areas are concerned, the real heavy lifting, so to speak, is done via changes in waves (both in terms of energy and direction), storm surges, and seasonal water level anomalies, all of which result from changes in the indices.
In effect, the indices are the cause (and here we use that term loosely) and the changes in waves, surges, and water level anomalies are the effect (also used loosely). These effects in turn drive local coastal changes, which can be drastically different depending on which side of the Pacific they are occurring.
To illustrate, let’s take an example close to home and relevant to this year’s big climate event: El Niño.
One of the researchers’ more significant findings — at least as far as we along the U.S. Pacific Northwest coast are concerned — notes that observed coastal erosion across the study area varies widely during El Niño years and La Niña years. In the Pacific Northwest, El Niño events have been linked to approximately 50 percent more coastal erosion than during normal winters, while La Niña events were linked to approximately 126 percent more coastal erosion as compared to an average (non-El Niño/La Niña) winter.
An analysis of the data by Barnard and colleagues showed that the substantially elevated wave energy during both El Niño and La Niña events was found to be the key driver of increased erosion. But that’s just our region. In contrast, erosion off New Zealand coasts was found to be 75 percent and 33 percent less than average during El Niño and La Niña events, respectively.
All this points to relationships between key Pacific Ocean basin-wide indices and regional climate impacts, relationships that, Barnard and colleagues note, in previous studies have been largely conjectured, but not shown definitively. According to the researchers’ analysis, these links between basin-wide indices and local impacts are stronger for some areas than for others, indicating that poorly understood local influences (for example, near shore hydrodynamics) should also be expected to have significant impacts.
The big takeaway from this study: While there is uncertainty in projections for changes in the climate indices reviewed here (especially El Niño and La Niña), this study serves to alert us to the fact that the climate impacts that our local coastal communities face are based in large part on changes that occur on both a large, global scale and over the long, decadal term. However, in our editorial opinion, given that there were only five El Niño/La Niña events during the period covered in this study, these findings should be considered as preliminary.