BALTEX Phase II 2003 – 2012. Science Framework and ...

BALTEX Phase II Science Framework and Implementation Strategy 29
A central concept is that of detection and attribution. The former is the identification of phenomena
beyond the range of undisturbed conditions. The latter concerns the causal linkage of such phenomena
to driving factors, including the anthropogenic ones.
Detection cannot be made relative to an absolute reference state, to which a change would be
contrasted. As no such period is available (i.e., a period that we would know was not affected by any
evolving external factor), detection should be attempted in relative terms, with respect to some chosen
reference period. In such a case, attribution studies could be designed in terms of incremental changes
in possible forcing factors. Obviously, the definition and characterization of the reference period needs
careful consideration. A practical choice might be the Climate Normal Period 1961-1990. Detection
should be a multi-parameter exercise, including a variety of statistical parameters, aspects like time
rates of changes, and others. Identification of such forcing factors that drive compensating changes is
an additional dimension of the work, as is checking for consistency in found phenomena across the
different components and aspects of the global and regional climate system. The choice of parameters
and processes relevant for detection studies should be guided by three main considerations: (i) chance
of detection (guidance from theory, past analogues and climate change projections), (ii) stakeholder
relevance and (iii) the likelihood of identification of the most likely underlying causes.
Given success in the detection studies, attribution can follow to attempt a quantification and separation
between different forcing factors. Sensitivity studies should be used to explore the different response
characteristics of the elements of the Baltic Sea basin system to potential forcing factors. This
knowledge is then used to determine the most likely combination of causes that can be attributed to the
observed variability and change. Coupled to this is the question of how much the climate system of the
BALTEX region is forced from the region itself, and how much is imported from outside the region.
Fig. 2.1 Ice break-up dates of the Tornionjoki river (Northern Finland) from 1693 until 2005 (by courtesy of
Raino Heino, FMI).
2.2.2. Projections of Future Climate Variability and Change
• To develop projections of future climate variability and change, by means of sensitivity
analyses and model studies.
In the construction of future regional projections and scenarios, the following three components should
be accounted for: i) unforced or natural variability of the global and the regional system, ii)
anthropogenically driven modifications of the global system (in terms of, e.g., air temperature, sea
level and circulation patterns), and iii) regional forcing scenarios for land and water use, the release of