RD&D-Programme 2004 - SKB

21 Climate
On the time scale for which the performance and safety of a final repository for spent nuclear
fuel are studied, i.e. hundreds of thousands of years and even longer, the Scandinavian climate
has undergone repeated ice ages. Over the past 800,000 years or so, a cyclic pattern has
dominated climate variation. A cycle consists of roughly 100,000 years long periods with a
progressively colder climate, known as glacials, ended by a rapid transition to shorter periods
with a warm climate similar to today’s, known as interglacials. During the glacial periods,
which consist of warmer and colder phases, ice sheets have successively – by repeated
advances and decays – grown to reaching a maximum extent towards the end of the period,
see Figure 21-1.
With a view towards the processes that are of importance for the performance and safety of a
deep repository, three characteristic climate-driven process domains can be identified during a
glacial period and the intervening interglacial periods. Climate-driven process domains, in the
following called climate domains, are defined as climate-determined environments in which a
number of characteristic conditions prevail. The three climate domains are:
• Glacial domain.
• Permafrost domain.
• Temperate/boreal domain.
The climate domains comprise a general description of the characteristic conditions, with an
emphasis on those processes that are of importance for the performance and safety of the deep
repository. Extremes, which can be made site-specific, can be identified within each climate
domain. Changes in the climate can be seen as variations of the extent of the climate domains
in time and space. The different climate domains succeed each other in a cyclical pattern, see
Figure 21-2. On any given site, the succession may not include all the climate domains shown in
the figure. On a high-lying site in southeastern Sweden, for example, a period with permafrost
may be followed directly by a temperate/boreal domain without an intervening period with
a glacial domain. Depending on the geographic location, the periods with different climate
domains will also differ in length.
It is reasonable to assume that the climatic progression we have seen over the past
800,000 years, with glacials succeeded by interglacials, will be repeated in the future. In
recent decades, man’s impact on the climate has been a much-debated scientific and social
issue. The debate has focused on human greenhouse gas emissions, which are believed to cause
global warming. Model simulations /21-1, 21-2/ show that as a result of human emissions of
Luleå
Kiruna
Malmö
Stockholm
100,000
50,000
0
Figure 21-1. Schematic drawing of the advance of the ice sheet during the most recent glacial
period – the Weichselian.
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