Manmade Climate Change Causing Sea Level Rise in Philippines, Northeast Australia

July 21, 2014

Ben Hamlington

A sophisticated new analysis of long-term sea level trends in the western tropical Pacific (WTP) Ocean indicates that climate change caused by humans is responsible for rising waters in the Philippines and northeast Australia, and that this rise will continue in the near future.

Benjamin D. Hamlington, an oceanographer at Old Dominion University, leads a team of scientists who report their findings in the journal Nature Climate Change. The article, "Uncovering an Anthropogenic Sea Level Rise Signal in the Pacific Ocean," debuted online on July 20, 2014.

During the past five years, Hamlington has been researching ways to better use satellite sensor data about sea levels. The data point to an overall rise in global sea level, but the rise is uneven in various regions of the world, including the WTP. Various research has buttressed the general belief among scientists that localized natural climate patterns involving winds and currents are a cause of these uneven measurements.

One such pattern is the Pacific Decadal Oscillation (PDO), which can have a major impact on sea levels in a region during one decade, but then have little or no impact the next. The PDO, of course, is not related to anthropogenic sea level rise, and is a factor that makes it difficult to assess the effect on rising seas of manmade climate change attributed to fossil fuel combustion and other greenhouse gas production.

Satellite altimetry measurements of sea levels give trustworthy measurements of global sea level, but they go back for only two decades. This, too, complicates long-range assessment of sea level trends.

Hamlington and his colleagues have looked to tidal gauges to augment the satellite data. Tidal gauges offer localized measurements dating back many decades, but don't have the global span of satellite altimetry. The researchers have crunched both sets of measurements together for the WTP to get a sea-level reconstruction. This data-rich reconstruction allows the researchers to "study the effect of longer-timescale natural climate variability on sea-level trends," as they report in the Nature Climate Change article.

Once the PDO effects were extracted from overall sea levels, the scientists found some interesting long-term trends.

"The prevailing thought has been that once the PDO shifts and changes phases, the sea level rise in the WTO will ease and future decades will hold much more manageable levels of sea-level change for the region," the article states. "Although this seems to be the case for areas near Indonesia, in the light of the results presented here, the high rate of sea level rise near the Philippines and northeastern Australia should not be similarly expected to abate over the next couple of decades."

The researchers point to other studies that have documented Indian Ocean warming caused by greenhouse gases and say they believe this anthropogenic forcing, and not natural climate forcing, is behind the trends in the Philippines and northeastern Australia.

"Ben Hamlington's paper with his international collaborators is a major contribution towards understanding the changing climate and its impact on sea level rise at very large scales," noted Rodger Harvey, chair of ODU's Department of Ocean, Earth and Atmospheric Sciences (OEAS). "He is a great addition to our faculty and brings important expertise that can help us better understand what our own region may face for sea level rise in the future."

Co-authors of the article are M.W. Strassburg, R.R. Leben and R.S. Nerem of the Colorado Center for Astrodynamics Research, University of Colorado; W. Han of the Department of Atmospheric and Oceanic Sciences, the University of Colorado; and K-Y Kim of Seoul National University, South Korea.

Hamlington joined the ODU OEAS department this summer as an assistant professor. He previously was a research associate at the Colorado Center for Astrodynamics Research, University of Colorado.