CLIMATE CHANGE AND OCEAN ACIDIFICATION - Marine Pollution: What Everyone Needs to Know - page 171

Why is sea level rising faster than was predicted?
The IPCC report in 2007 projected a global SLR between 0.2-
0.5 m by the year 2100. Current measurements meet or exceed
the high end of that range, however, and suggest a rise of 1 m
(3.3 feet) or more by the end of the century. The reason for the
underestimate is that the models did not include critical feed-
backs that speed everything up. These feedbacks are melting
of Arctic sea ice and the Greenland ice cap. While ice is bright
and reflects much of the sun's radiation back (this is called
albedo), water is dark and absorbs it, causing more warming.
Melting sea ice—which is already in the ocean—does not itself
raise the sea level, but when it melts it releases more freshwa-
ter from the Arctic, which is then replaced by inflows of saltier
warmer water from the south. That warmer water pushes the
Arctic toward more ice-free waters, which, because of their
dark color, absorb sunlight rather than reflect it back into
space the way ice does. The more open water there is, the more
heat is trapped in the water, and the warmer things can get.
There are gigantic stores of ice in Greenland and Antarctica
that are melting. This was clear in the summer of 2012 when
Greenland had a record-setting melt. Another missing feed-
back is the groundwater being extracted all over the world
to mitigate droughts. That water is ultimately added to the
oceans. All these feedbacks will speed up SLR.
What can be done about sea level rise?
A major challenge is how to both mitigate and adapt to the
impacts of climate change since impacts are now inevitable
even if aggressive action is taken quickly to reduce greenhouse
gas emissions, which seems unlikely. In order to protect coastal
cities and towns, adaptation involves improving and increas-
ing salt marshes and mangroves that reduce storm surges, and
building sea walls and other structures to hold back the ocean.
Restoring and constructing coastal wetlands, oyster reefs, and