Sea Level Rise and Coastal Impacts

A new study on sea level rise trends and potential impacts and was published last week in Science, Robert J. Nicholls & Anny Cazenave, Sea-Level Rise and Its Impact on Coastal Zones, 328 Science 1517-1520 (2010) (subscription required).

This would be an excellent student reading because it updates the assessments of the IPCC’s 4th Assessment and reminds students that non-climatic factors can work in tandem with climate change to produce negative impacts. Among the article’s take-aways:

  1. While the IPCC’s 4th Assessment Report projected that global seal level could rise up to 60 cms., it failed to adequately account for ice sheet dynamics. Recently identified accelerated decline of polar ice sheet mass now raises the prospect of sea level rise of 1 meter by 2100;
  2. While sea level rise was nearly stable since the end of the last deglaciation, sea level rose by an average of 1.7 mm/yr. since 1950, and this accelerated to 3.3 mm/yr. from 1993-2009;
  3. Thermal expansion accounts for about 50% of sea level rise from 1993-2003; the glacial contribution to sea level rise from 1993 to 2009 may be 30%. A substantial non-climatic contributor has been factors e.g. ground subsidence due to oil and groundwater extraction, irrigation, and most importantly, intensive dam building along rivers, lowering sea level by about 0.5 mm/yr. in the 20th Century;
  4. Greenland and West Antarctica mass loss is accelerating, and contributed to 15% of global sea level rise from 1993-2003, with that contribution doubling since 2003;
  5. The largest unknown factor in future sea level rise is the behavior of ice sheets. Future ice dynamics could result in sea level of 80 cms. by 2100, with overall projections of one study of sea level rise of 30-180 cms. by 2100, this upper limit obviously being far above the 4th Assessment projections;
  6. While immediate effect of sea level rise is submergence and increased flooding of coastal lands and saltwater intrusion of surface waters, longer-term effects include increased erosion and saltwater intrusion into groundwater, declines of coastal wetlands such as saltmarshes and mangroves;
  7. In many areas, non-climatic relative sea level rise predominates; including in most river deltas;
  8. Most countries in South, Southeast and East Asia are highly threatened by sea level rise because of widespread occurrence of densely populated deltas. In Africa, there are serious threats due to low levels of development combined with expectations of rapid population growth in coastal areas. Small island states are, however, the most threatened nations, with some facing “the real prospect of submergence and complete abandonment during the 21st century;”
  9. Adaptation can ameliorate impacts under some circumstances; however, protection can also attract new development in low-lying areas, increasing risks.

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