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Today’s good news, about rising sea levels

3 June 2010

Summary:  There has been much evidence that the terrible tales of rising sea levels are exaggerated.  Slowly hard evidence emerges.

Contents

  1. Shape-shifting islands defy sea-level rise“, New Scientist, 2 June 2010
  2.  “The dynamic response of reef islands to sea level rise: evidence from multi-decadal analysis of island change in the central pacific“, Arthur P. Webb and Paul S. Kench , Global and Planetary Change, in press
  3. Other articles about rising sea levels
  4. For more information, and an Afterword

Excerpts

 (1)  Shape-shifting islands defy sea-level rise“, New Scientist, 2 June 2010 — Excerpt:

For years, people have warned that the smallest nations on the planet – island states that barely rise out of the ocean – face being wiped off the map by rising sea levels. Now the first analysis of the data broadly suggests the opposite: most have remained stable over the last 60 years, while some have even grown.

Despite this, Kench and Webb found that just four islands have diminished in size since the 1950s. The area of the remaining 23 has either stayed the same or grown.

Paul Kench at the University of Auckland in New Zealand and Arthur Webb at the South Pacific Applied Geoscience Commission in Fiji used historical aerial photos and high-resolution satellite images to study changes in the land surface of 27 Pacific islands over the last 60 years. During that time, local sea levels have risen by 120 millimetres, or 2 millimetres per year on average.

 (2)  The article:  “The dynamic response of reef islands to sea level rise: evidence from multi-decadal analysis of island change in the central pacific“, Arthur P. Webb and Paul S. Kench , Global and Planetary Change, in press — Abstract:

Low-lying atoll islands are widely perceived to erode in response to measured and future sea level rise. Using historical aerial photography and satellite images this study presents the first quantitative analysis of physical changes in 27 atoll islands in the central Pacific over a 19 to 61 year period. This period of analysis corresponds with instrumental records that show a rate of sea level rise of 2.0 mm/year in the Pacific.

Results show that 86% of islands remained stable (43%) or increased in area (43%) over the timeframe of analysis. Largest decadal rates of increase in island area range between 0.1 to 5.6 hectares. Only 14% of study islands exhibited a net reduction in island area.  Despite small net changes in area, islands exhibited larger gross changes. This was expressed as changes in the planform configuration and position of islands on reef platforms. Modes of island change included:

  • ocean shoreline displacement toward the lagoon;
  • lagoon shoreline progradation; and,
  • extension of the ends of elongate islands.

Collectively these adjustments represent net lagoonward migration of islands in 65% of cases. Results contradict existing paradigms of island response and have significant implications for the consideration of island stability under ongoing sea level rise in the central Pacific.

  • First, islands are geomorphologically persistent features on atoll reef platforms and can increase in island area despite sea level change.
  • Second; islands are dynamic landforms that undergo a range of physical adjustments in responses to changing boundary conditions, of which sea level is just one factor.
  • Third, erosion of island shorelines must be reconsidered in the context of physical adjustments of the entire island shoreline as erosion may be balanced by progradation on other sectors of shorelines.

Results indicate that the style and magnitude of geomorphic change will vary between islands. Therefore, Island nations must place a high priority on resolving the precise styles and rates of change that will occur over the next century and reconsider the implications for adaption.

(3)  Other articles about rising sea levels

(4a)  For more information on the FM site

Reference pages about other topics appear on the right side menu bar.  Of special relevance to this topic are:

(4b)  Afterword

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