Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 275

sion. Warm water occupies more space than cold water. The importance of this often does
not reach the public eye.
Given all these regional factors that can influence sea level, it is not surprising to learn
that there is a great deal of global regional variation in measurements of sea level rise. For
example, sea level rise in north-western Europe is lower than in many other areas. We will
come back to this later, but for the next few paragraphs, we will just consider estimates of
global mean sea level. Remember, though, that the global mean sea level is a hypothetical
entity even if you are measuring it today because in reality, wherever you are, the real sea
level is likely to be above or below the mean.
What do we know about recent changes in global mean sea level? Prior to 1880, the
global mean sea level had been more or less stable for several thousands of years. This is
no longer the case. According to the U.S. Environmental Protection Agency's (EPA's) 2012
Report on Climate Change Indicators , the global mean sea level rose by about 22.9 cm (9
inches) between 1880 and 2011. The rate of rise is increasing. IPCC AR5 estimated that
“[i]t is very likely that the global mean sea level rise was 1.7 (range 1.5 to 1.9) mm per year
between 1901 and 2010, 2.0 (1.7 to 2.3) mm per year between 1971 and 2010, and 3.2 (2.8
to 3.6) mm per year between 1993 and 2010.” 15
The present estimate is that about 57% of the observed mean global sea level rise
since 1993 is due to the thermal expansion of water as the sea warms up, 28% from melting
mountainglaciersandtheremainderfrommeltinglossfromthelargepolaricesheets(West
Antarctica and Greenland). Notice the size of the contribution from the thermal expansion
of water. Even if the polar ice sheets could miraculously be prevented from melting, the
thermal expansion will still lead to a rising global mean sea level.
What does all this mean in relation to global mean sea level for the future? At the time
of writing, IPCC AR5 estimates that “sea level rise for 2081-2100 relative to 1986-2005
will likely be in the ranges of 0.26 to 0.55 m for RCP2.6; 0.32 to 0.63 m for RCP4.5; 0.33
to 0.63 m for RCP6.0; and 0.45 to 0.82 m for RCP8.5 (medium confidence)” 16 . This is still
less than that suggested by many climate scientists. Take a look at the papers referenced by
Bamber et al. ( 2013 ), Rahmstorf ( 2007 ), Rahmstorf et al. (2012) and Schaeffer et al. ( 2012 )