Qualitative assessment of biodiversity impacts

A complete quantitative comparison of the three scenarios described above is not possible since, notwithstanding the discussion above, the scenarios are based on storylines including qualitative elements. Therefore the collective expertise of the ALARM consortium was distilled into a qualitative assessment of relative impacts on biodiversity. This involved developing a consensus about what pressures and aspects of biodiversity should be assessed, and the subsequent adoption of common qualitative impact scales to be used by all respondents to a questionnaire. Biodiversity impacts were assessed in the year 2050 for each of seven biomes at ecosystem and sub-ecosystem (species-group) levels for each of five key pressures and three scenarios discussed above. Experts in the ALARM project were asked to make such assessments only where they had expert knowledge, but wherever such an assessment was made they were asked to score all three scenarios. Figure 1 shows the proportion of possible assessments for each biome that were made.

Figure 1. Proportion of possible assessments for each biome

Comparing the scores of impacts on biodiversity assigned to each scenario for each combination of pressure, aspect of biodiversity and biome reveals a picture of the differences between the scenarios that is relatively robust to differences in the way individuals qualitatively score risk (see figure 2). Using this approach shows that impacts on biodiversity under SEDG are less severe than the impacts under BAMBU which in turn are less than the impacts under GRASThis result holds at the European level and when broken down into individual biomes. However, there is considerable variability in this overall response, for example, when comparing any two scenarios the majority of assessments showed no differences, and a small number go against the overall trend e.g. 2% of assessments have a higher impact under SEDG than under BAMBU.

Figure 2. Scores of impacts on biodiversity assigned to each scenario for each combination of pressure