climate change on UAE - Stockholm Environment Institute-US Center

2. Sea-level Rise Impacts
on Coastal Systems
Coastal zones are one of the most vulnerable
areas to <strong>climate</strong> <strong>change</strong> given the increased
certainty of a rise in mean sea level. As mentioned
earlier, the IPCC’s Fourth Assessment Report,
posits an upper boundary for global sea-level
rise by 2100 of 0.59m. Beyond 2100, sea level
rise projections are increasingly dependent
on emissions scenarios (IPCC, 2007). Sea level
<strong>change</strong>s are induced by both natural factors
such as changing ocean basin volume and
depth as the earth’s plates separate and collide
with each other, as well as deglaciation from
anthropogenic global warming.
Taking a step back to clarify the terms used,
mean sea level (MSL) is the average level of the
sea’s surface, as measured relative to a fixed
level on the land. MSL is typically calculated
over long periods, usually averaged over the 19
year lunar cycle as it smoothes tidal variations.
There are seasonal or annual <strong>change</strong>s in MSL
in addition to gradual increases in MSL that
scientists have tracked over time.
Deglaciation of continental ice caps, in
particular, can <strong>change</strong> sea level by tens of
meters (Emery and Aubrey, 1991). Deglaciation
<strong>change</strong>s the volume of water in the ocean,
which is known as a eustatic sea level <strong>change</strong>.
The IPCC estimates, however, do not include
ice-sheet dynamics even though over a long
time frame, more than 10 meters of sea-level
rise is possible, depending on the emission
scenario and assumptions regarding ice-sheet
dynamics (IPCC, 2007). Figure 2-1 shows a
breakdown of contributing factors to mean sea
level rise. As the IPCC explains, the data in this
figure are for 1961 to 2003 (light blue) and 1993
to 2003 (dark blue). The bars represent a 90%
error range. Sea level <strong>change</strong> is the sum of the
upper four entries (thermal expansion through
Antarctica) in addition to the observed rate of
rise. For the sum, the error has been calculated
as the square root of the sum of squared errors
of the contributions; to obtain the error for the
difference, combine errors of the sum and the
observed rate (IPCC WGI, Chapter 5).
Researcher Dr. Vivien Gornitz, jointly posted
at the Columbia University Center for Climate
Systems Research and NASA’s Goddard
Institute for Space studies, explains global
trends further. She writes that 20th century
global sea level, according to tide gauge data,
has been increasing by 1.7-1.8 mm/yr and that
most of this rise is due to ocean warming and
mountain glaciers melting, which have receded
dramatically in many places especially during
the last few decades. She continues, “since
1993, an even higher sea level trend of about 2.8
mm/yr has been measured from the TOPEX/
POSEIDON satellite altimeter. Analysis of
longer tide-gauge records (1870-2004) also
suggests possible late 20th century acceleration
in global sea level” (Gornitz, 2007). Computed
from satellite altimetry from January 1993
to October 2005, Figure ‎2‐2 captures these
variations in global mean by plotting the
Impacts, Vulnerability & Adaptation for
Coastal Zones in the United Arab Emirates
Figure ‎2-1. Estimates of the various
contributions to global mean sea level <strong>change</strong>.
Source: (IPCC, 2007)
Figure ‎2‐2. Variations in global mean sea level.
Source: (IPCC WGI, 2007)
17