CFAN Special Report on Sea Level Rise & Climate Change
This Report assesses the scientific basis for projections of future sea level rise. The following four issues frame this Report:
Whether recent global sea level rise is unusual.
At least in some regions, sea level was higher than present around 5000 to 7000 years ago. After several centuries of sea level decline following the Medieval Warm Period, sea levels began to rise in the mid 19th century. Rates of global mean sea level rise between 1920 and 1950 were comparable to recent rates. It is concluded that recent change is within the range of natural sea level variability over the past several thousand years.
The extent to which recent global sea level rise is caused by human-caused global warming, relative to natural causes of global sea level rise.
The slow emergence of fossil fuel emissions prior to 1950 did not contribute significantly to 19th and early 20th century sea level rise. Identifying a potential human fingerprint on recent sea level rise is confounded by the large magnitude of natural internal variability associated with ocean circulation patterns. There is not yet any convincing evidence of such a fingerprint on sea level rise associated with human-caused global warming.
The extent to which local sea level rise is influenced by the global sea level rise, relative to local vertical land motion and local land use practices.
In many of the most vulnerable coastal locations, the dominant causes of local sea level rise problems are natural oceanic and geologic processes and land use practices, notably landfilling in coastal wetland areas and groundwater extraction.
The amount of sea level rise (global and local) projected for the 21st century.
Local sea level in many regions will continue to rise in the 21st century – independent of global climate change. There are numerous reasons to think that projections of 21st century sea level rise from human-caused global warming are too high, and some of the worst-case scenarios strain credulity.
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