5. Uncertainties about Climate Change in EAs

The main focus of this study is to address uncertainties about climate change in project EAs. Although there is broad agreement among climate scientists about the mechanisms of, and general trends in global warming, there are significant uncertainties about some key aspects of climate change and its effects (Harvey, 2000; Miller, 2002). Examples of these uncertainties include:

1. the average global temperature increase that would result from specific increases in greenhouse gases;
2. the effects on regional climate variables such as temperatures, precipitation, and wind, and their fluctuations;
3. the effects of projected climate change on systems such as agriculture, oceans, ice sheets, and terrestrial ecosystems;
4. the spread of diseases and other related hazards to human health; and
5. the resulting effects on socio-economic systems such as jobs and health care.

The implications of these issues at the global level can be enormous, and need to be addressed through policies and plans at a large scale (e.g., national or sectoral), as well as through decisions on individual projects that can be affected by climate change, and that cumulatively can have significant effects on climate change.

In general, the most needed climate information required for project-specific EAs concerns the specific climate for the region in which the project is being undertaken. Unfortunately, any determination of specific predictions at the regional level of detail requires the production of climatic information in which there is the least degree of confidence. Furthermore, there are likely to be many highly uncertain future relationships between climate change and various other biophysical, social, and economic impacts. Using the previous fishery example, significant uncertainties about the effect of climate change on the fishery both with and without any proposed upstream dam may exist.

Figure 2, which is a modified version of figure 1, illustrates the effect of uncertainties about climate change on the prediction of project impacts. Uncertainties about the "without project" and "with project" environmental conditions are shown as bands, and the differences between them, shown by the arrow, represent widely uncertain predictions about the effects of the project.

Figure 2. Effect of Uncertainties on Impact Prediction

As the relationship between climate change and any potentially affected environmental components becomes less direct, the uncertainties can become more pronounced. Using an example where climate change will affect precipitation in a watershed and water in the river is used for irrigation purposes, the relationships between rainfall and streamflow, streamflow and irrigation, irrigation and agricultural production, agricultural production and farm jobs, and farm jobs and the local economy are all uncertain to varying extents. Also, the cumulative effects of these chains of uncertainties would make the prediction of the impacts of climate change on the regional economy highly uncertain. Irrespective of these uncertainties, decisions must be made; understanding and addressing these inherent uncertainties is better than ignoring them when making decisions.

The extent of any adaptation and mitigation activity proposed during the EA process should depend upon the uncertainties in the impacts determined during the analysis of the project, which in turn depends inherently upon the range of uncertainties and assumptions made regarding future climate change. At the project level, there may be many ways to lessen vulnerabilities due to the uncertainties, and these mechanisms should be considered in an assessment. For example, for a hydroelectric project, uncertainties about climate change create uncertainties about streamflows, which in turn create uncertainties about energy production and downstream fisheries and flooding. While very little may be done to proactively prevent the uncertain future streamflows caused by a changing climate, the project itself, could be modified, designed and/or operated to reduce the effects of, and vulnerabilities to the remaining uncertainties. Because of these uncertainties, an entirely different site or even a different type of electric project might be selected. Alternatively, the hydroelectric project might be modified to include an accompanying reservoir that would be sized and operated to reduce the uncertain risks of downstream flooding. Flexibility and robustness can be built into projects, and their EAs should address the monitoring of both climate change and projects' responses to climate change, e.g., the effectiveness of the mitigation and adaptation measures. Also, EAs should set out contingency plans for how to respond to unforeseen changes. Such project response efforts are, however, outside the scope of this study.