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Global Coastal Populations at Risk as Sea Level Continue to Rise
Global mean sea level has risen by 212.6 millimeters (mm) since 1880. 1 (See Figure 1.) And the rate of increase is accelerating.2(See Figure 2.) Overall, the global mean sea level has risen 1.65 mm per year since 1880.3 But average sea level rise from 1993 to 2009 was almost double that long-term rate, at 3.2 mm per year.4 This apparent acceleration is a matter of concern because some 10 percent of the world lives along a coast; as sea level continues to rise, these people will be threatened by further inundation by the sea and stronger storm surges.5
The evidence of climate change as a result of increases in greenhouse gas since the industrial revolution is readily evident, and the Intergovernmental Panel on Climate Change (IPCC) restated in its 2013 report that it is “extremely likely” these changes are driven by human actions.6 The atmospheric carbon dioxide level, which did not rise above 300 parts per million (ppm) in the 650,000 years before 1950, currently sits at around 398 ppm.7 This increase has led to stronger radiative warming of Earth, and the global mean surface temperature increased 0.85 degrees Celsius between 1880 and 2012.8 Perhaps more alarming is the increase of 0.72 degrees Celsius just from 1951 to 2012.9 This acceleration in surface temperature increase reflects acceleration in the rise in atmospheric carbon dioxide concentration. From 1980 to 2011, the concentration rose at 1.7 ppm per year, but the rate was 2 ppm from 2001 to 2011.10
The ocean absorbed over 90 percent of the excess heat energy from 1971 to 2010, and this increase in the ocean's energy content led to a rise in ocean temperatures.11 In the top 700 meters of water, the ocean has warmed 0.302 degrees Celsius since 1969.12 An increase in ocean temperature is critical because thermal expansion of ocean water is responsible for a substantial part of sea level rise.
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