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Research Report

Climate Scenarios:: What we need to know and how to generate them

Heru Santoso
Monica Idinoba
Pablo Imbach
Copyright Date: Dec. 1, 2008
Pages: 32
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Table of Contents

  1. (pp. 5-5)

    Climate change profoundly affects the natural and social environment. For example, changes in seasonal to interannual climate strongly affect agricultural production, the quantity and quality of water resources, and resources coming from land and marine ecosystems. IPCC (2007b) indicates several key impacts on different sectors that are correlated with climate change such as freshwater resources and their management; ecosystems; food, fibre and forest products; coastal systems and low lying areas; industry, settlement and society; and health.

    Decision-makers and resource managers require information regarding future changes in climate average and variability to better anticipate potential impacts of climate change. However, future...

  2. (pp. 6-7)

    Dessai et al. (2005) discussed the role of climate scenarios in three different types of adaptation approaches. They are the IPCC approach, human development approach, and risk approach. This section summarises each approach in the context of whether the climate scenario is needed or not.

    IPCC approach follows a traditional approach of impact assessment in which using climate scenario is an important step towards adaptation planning (Dessai et al. 2005). In the case of adaptation programme in the multinational Mekong river basin in South East Asia², for example, a highly quantitative impact assessment through modelling was employed to estimate the...

  3. (pp. 8-8)

    The climate data or climatological information required by impact analysts varies enormously depending on types of studies. Some factors to consider in using climate information, and relevant for base line and projected impact studies, are listed below. The list is extracted from the IPCC General Guidelines on the Use of Scenario Data for Climate Impact and Adaptation Assessment (IPCC-TGICA 2007).

    Variables: The climate variables required are dependent on the impact models used. The most common variables in impact studies are surface observations of air temperature and precipitation. Some impact models require a larger set of variables as input, such as...

  4. (pp. 9-10)

    The Intergovernmental Panel on Climate Change – Task Group on Data and Scenario Support for Impact and Climate Assessment (IPCC-TGCIA) classified climatic scenarios into three main types (IPCC-TGICA 2007), based on how they are constructed. These are: synthetic scenarios, also known as incremental scenarios (IPCC 2001); analogue scenarios and climate model based scenarios.

    The construction of synthetic scenarios or incremental scenarios involves a technique by which particular climatic elements are changed by a realistic arbitrary amount, for example, adjustment of temperature variable by +1, +2, and +3°C from a reference state (baseline), or increase or reduction of precipitation by 5%,...

  5. (pp. 11-11)

    The IPCC Special Report on Emissions Scenarios (SRES) in replacing the old IPCC scenarios (IS92) identifies 40 different scenarios following four families of story lines. Six illustrative scenarios were drawn from these four families: A1FI (fossil intensive), A1T (predominantly non fossil), A1B (balanced across energy sources), A2, B1 and B2 (Nakićenović et al. 2000) (see Box 2). All emission scenarios were designated as equally valid and probable (IPCC-TGICA 2007).

    Impact analysts may use non-IPCC SRES scenarios for specific interests. For example, unavoidable scenario with greenhouse gas emission is at year 2000 level. This scenario is practically unattainable and therefore invalid....

  6. (pp. 12-13)

    GCMs are run by a number of centres. Some differences exist among the models, which result in various climate sensitivities⁴ in a range likely between 2.0°C and 4.5°C with a best estimate value of 3.0°C (Solomon et al. 2007). For sensitivity analyses, it is often useful to consider the results of several models when constructing the scenarios. However, users may find selecting appropriate models difficult especially when many models are available with various projection results (some models may show diverging results).

    Some criteria for selecting climate models are suggested in Smith and Hulme (1998) and IPCCTGICA (2007):

    Vintage. Recent models...

  7. (pp. 14-15)

    Selection of appropriate spatial resolutions in assessing impacts or ecosystem response to climate change depends on the objective of the modelling and accompanying technical factors (see also chapter 6). In general, finer resolution data are better than coarser ones for the purpose of database building to serve various studies and impact assessments of different scales, but finer resolution data need bigger data storage capacity than coarser data.

    There are simple guidelines for handling the climate data in the context of spatial scale (Price and Flannigan 2000).

    It is easier to aggregate appropriately from fine resolution data than it is to...

  8. (pp. 16-16)

    Aggregating temporal resolution data, for example from daily to monthly is a straightforward process by calculating the average or sum of the fine resolution data over the coarse temporal resolution. Aggregating fine temporal resolution data into coarse resolution will lose important climate variation (eg daily variation of precipitation or daily maximum temperature) to be replaced by a single value of the sum or the average.

    Disaggregating temporal resolution data, for example from annual data to monthly data or monthly to daily, is a more complex process. It is similar with a process to create synthetic data. Weather generator is a...

  9. (pp. 17-18)

    Many climate scientists, science funding agencies and decision makers positioned climate scenarios as the core of adaptation, and reducing uncertainties in the climate projection is crucial (Murphy et al. 2004; MOHC 2007 in Dessai et al. 2008). Knowing the fact that the uncertainty cannot be separated from climate scenarios (see Box 6) has led to a tendency to quantify the uncertainties of climate scenario as a guide for effective adaptation strategies, especially if the climate scenario shows a range of possible future climates the region of interest may experience, which shifted the science in climate projections from deterministic climate to...

  10. (pp. 19-19)

    The link between natural climate variability and change with local and regional occurrence and severity of extreme events begins to disclose (Bader et al., 2008). Extreme events such as hurricane, floods, droughts and land and forest fires have enormous societal and environmental implications. Evidences exist to indicate that some natural climate variations, such as ENSO, are in connection with extreme events (Solomon et al. 2007).

    Some GCMs can now simulate important aspects of ENSO, but there are still large uncertainties about their amplitudes and variability (Meehl et al. 2000; Meehl et al. 2007). What factors trigger the mechanism of this...

  11. (pp. 20-21)

    The secretariat of the United Nations Framework Convention on Climate Change (UNFCC) produced the Compendium on Methods and Tools to Evaluate Impacts of, and Vulnerability and Adaptation to, Climate Change (UNFCCC Secretariat 2008). It provides key information on available frameworks, methods and tools, and their special features. It is designed to assist parties to the Convention and other potential users in selecting the most appropriate methodology for assessments of impacts and vulnerability, and preparing climate change adaptation. Parties are obligated by the Convention and various decisions of the Conference of the Parties to assess their national-level impacts of climate change...

  12. (pp. 22-22)

    The role of climate scenarios in adaptation assessment and planning ranges from irrelevant to highly relevant depending on the approach, which is determined by nature of the case, scale of the area, climate data availability and capacity to handle them, and time scale.

    If climate scenarios are available and reliable (ie they depict plausible future climate), they are always beneficial for picturing future climate and understanding its impacts. They are also useful, and probably more import, for testing the robustness of adaptation response or policies, despite their uncertainties.

    Communicating climate scenario to users (decision makers, resource managers and planners etc)...