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

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30 BALTEX Phase II Science Framework and Implementation Strategy substances, and other management issues relevant for the environment. Future projections and scenarios should address also the unavoidable uncertainties embedded in the driving global and regional scenarios due to the inherent uncertainties in the climate system science and the evolution of climate system forcing on both the regional and global scales. 2.3. Involvement of Stakeholders The stakeholders with interest in this major objective of BALTEX Phase II are i) the public at large, ii) national authorities with responsibility for e.g. infrastructure and the environment, iii) international agencies and organizations including the European Environment Agency (EEA) and the Intergovernmental Panel on Climate Change (IPCC), and iv) actors involved in policy-making, enterprises, and corporate institutions that need to factor changing climate into long-term planning decisions. On the one hand, stakeholders require reliable and useful knowledge about past climate change, present variability and the occurrence of extreme and rare events 3 . Also, stakeholders increasingly need detailed, consistent and useful descriptions of possible and plausible future climate variability and change. Of special concern are the identification of robust changes and the separation of these from more uncertain ones. Another major goal should be a simplification of the issues, such as ruling out those facets of climate change that are not significant for a particular stakeholder. On the other hand, research needs knowledge from stakeholders. Plausible and possible perspectives for changes of land use, river regulations, regional emissions of aerosols, and other regional or local agents influencing the regional and local climate are required for comprehensive future projections and scenarios. Stakeholders should also be encouraged to provide scenarios of other anthropogenic factors (e.g., release of harmful substances), which will influence the BALTEX region (e.g., ecosystem functioning) in conjunction or in addition to climate forcing and change. This latter aspect is especially important in the context of extensions of BALTEX data and modelling studies beyond the physical climate system. 2.4. Potential Activities 2.4.1. Reconstruction History of Climate in the past 200 Years as well as Detailed Reanalysis of “Weather” of the past 40 Years Regional re-analysis as well as other reconstructions are needed in studies of climate variability and change. One focus will be on the past 200 years which allows for studies on natural climate variability, the action of natural forcing factors, and extremes, see below. Another focus will be on the past 40 years, where the increasing range of novel observations and measurement campaigns allows for increasingly more physical and targeted basic and applied process studies, and model evaluation. The availability of global re-analyses such as ERA-40 and NCEP (National Centres for Environmental Prediction) products give a particular rational for the past 40 years. The focus on the past few decades will also contribute to better understanding of the physical background of the processes which determine the water and energy cycle in the Baltic Sea basin, as described in more detail in Chapter 1.4.1. In this context, BALTEX Phase II is in line with the World Climate Research Programme/Coordinated Observation and Prediction of the Earth System (WCRP/COPES) strategy which suggests using the 1979-2009 period to develop reference climate data sets and advanced forecasting techniques (see also Chapter 10). The variables considered are foremost the conventional geophysical ones describing the atmosphere, hydrology, the ocean and sea ice. For much of the period, available data allow the reconstruction of state variables. In the second half of the 20 th Century, possibilities to address process-level 3 Here, we refer not only to extreme events that occurred and have caused major consequences, but also to the likelihood of the occurrence of events being normal but at the same time rare.
BALTEX Phase II Science Framework and Implementation Strategy 31 observational data, such as on fluxes, increase, which should be exploited. Addressing quantities such as land use and ecosystem-based indicators is also a new application topic. Valuable and so far unused information on the past climate of the Baltic Sea basin exists and needs to be identified, collected and made available in digital form for further processing. Past data may need homogenization, i.e., it must be ensured that their information content does not change over time, for example through influences by changing observation procedures or local conditions. For provision of accurate past and present climate data, assimilation is essential. However, regional reanalysis by means of models without data assimilation is needful when evaluating and developing models to be applied for, e.g., future projections. Models without assimilation give rise to biases in parameters and also phase-shifts. However, off-line models or models with assimilation can host spurious sources and sinks and thus mask "bad model behaviour" or give rise to unphysical behaviour. Thus, re-analysis data sets with no assimilation, i.e. model runs in climate mode for the past and present periods are also needed. Reconstruction methods should include dynamical downscaling with limited area models for the atmosphere, ocean and hydrology as well as statistical downscaling and extrapolation techniques. Given that the amount of directly acquired data diminishes with "backwards time", proxy data are needed to complement direct measurements in time, physical space and parameter space as well as for cross-evaluations. Again, this has bearing on (multi-) decadal variability and detection. In addition to existing proxy data, such as from tree rings, the inclusion of new proxy data sets will be valuable for regional (multi-) decadal variability and detection studies. Within this chapter, re-constructed and reanalysed data are especially needed for potential activities described in sections 2.4.2 and 2.4.4. Fig. 2.2 Annual maximum Baltic Sea ice extent since 1720, expressed as deviation from the long-term mean. Data based on various types of observations (data by courtesy of FIMR). 2.4.2. Detection and Attribution of Climate Change Signs of long-term change and apparent emergence of extreme weather need to be assessed for possible consistency with natural low-frequency variability and rare but nevertheless normal extreme events, or whether they are indicators of ongoing systematic change outside the conventional climate and weather variability. In the latter case, climate change is “detected”. Possible causes are then
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