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Ever tried putting numbers into an assessment of climate vulnerability? A standard approach starts with scoring Exposure, Sensitivity and Adaptive Capacity.This blog is about assessing Exposure to climate change.

Exposure is the change in climate that may be experienced. Armed with modeled projections of climate change, it sounds fairly straight forward – but that isn’t always the case. Exposure can be considered in three ways:

  • Absolute level – e.g. the baseline mean annual temperature was ‘a’ and the projected change is to ‘b’. This works well if there are known sensitivity thresholds; e.g. alpine species don’t persist if mean summer temperatures are above a certain level, or certain vegetation types won’t be found in areas with a mean annual rainfall below a certain level. However, we often don’t know what those threshold levels are.
  • Amount of change – i.e. the difference between projected and baseline measures (‘b ‘ less ‘a’); such as a 5 C increase in average temperature. These metrics give us a feel for how much change is likely, allowing initial contemplation of the likely impacts. However, the approach can suggest that a set amount of change has uniform consequence across a region, which may not be so – especially if the starting points are not uniform.
  • Percentage change – i.e. the relative difference (‘b-a / a’ X 100). This approach requires more computing but considers the starting point, giving a better appreciation of the comparative change. However, problems arise in computing percentages when some baseline points (‘a’) are zero.

The challenges outlined above are particularly evident when making assessments across a landscape where baseline measures are different to begin with and changes are not spatially uniform either. It seems that the approach taken to measuring change may rest on the level of understanding of the system being assessed (e.g. threshold levels), the data (e.g. the presence of zero baseline levels), and on the computing power, and time, available.

I’m interested to hear how others have worked through these options and any ‘tips for young players’ they may have.

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