period in the last 500 years. These rising temperatures
Global mean sea level
unavoidably have an influence on very diverse natural
phenomena that we so far have taken for granted.
Change of sea level

in centimetres
Evidence of a warming world includes shorter freezing
+ 20
seasons of lake and river ice, decreases in the extent
of permafrost, and rising soil temperatures. But the
main changes observed scientifically, but also noticed
more and more by the people all over the world are
+ 10
summarized in the following paragraphs.
Sea level rise
Sea levels across the globe have risen in a way con-
1870 level
0
sistent with the warming – since 1961 at an average
Tide gauge observation
of 1.8 millimetres per year, and since 1993 at 3.1
66 and 95% confidence limits
millimetres per year. Scientists are not sure whether
Satellite altimetre observations
to attribute this last decade’s higher rise to a varia- - 10
tion from one decade to another, or whether it marks
1880 1900 1920 1940 1960 1980 2000
a longer-term trend. The total global rise in the 20th
1870 2005
century amounted to 17 centimetres. The expansion
Source: Hugo Ahlenius, GRID-Arendal 2008, updated from Church and White 2006.
What causes the sea level to change?
Terrestrial water storage,
extraction of groundwater,
builing of reservoirs,
Surface and deep ocean
changes in runoff and
ciruclation changes and storm surges
seepage into aquifers
Water stored on land
Lowered surface level
as glaciers and icecaps
in river delta regions,
breaks off or melts and
Higher temperatures cause
land movements and
becomes ocean water
the water to expand
tectonic displacements
Source: Philippe Rekacewicz (GRID-Arendal) Vital Climate Graphics 2002, based on: David Griggs,
in Climate Change 2001, Synthesis report, contribution of working groups I, II and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, 2001.
Present changes, causes and observed impacts 9
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