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Potential impact projection

Potential impact projection methods analyse the possible impact of climate change and other potential drivers on an exposed system in the absence of adaptation. Modelling tools tend to be available only for certain sectors such as agriculture, water resources, coastal zones, and terrestrial ecosystems. Models vary enormously in their complexity, in the spatial and temporal scale of their application, and in their assumptions about adaptation, but the process of impact projection is generally the same: select climate and socio-economic scenarios, select adaptation options and strategies, then compute impacts.

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Potential impact projection does not include adaptation of actors in projecting impacts. Impact projection methods analyse the possible impact of climate change and other potential drivers on a study unit. The fundamental theoretical assumption of impact analysis is that it is possible to analytically distinguish between a study unit and its (natural and socio-institutional) environment in the sense that the environment influences the study unit but whatever happens "inside" the study unit does not feed back on its environment. This separation allows for the representation of the evolution of the environment in form of a set of scenarios that are independent from the model used to represent the study unit. If changes in the study unit would influence the environment, than an integrated (assessment) model would need to be used for representing both the study unit and its environment together. We follow the IPCC in distinguishing methods that analyse potential impacts, which are those that "may occur without considering adaptation" (Parry et al. 2007: 876), in opposition to methods that assess residual impacts, which include adaptation. One problematic aspect about potential impact assessments is that the theoretical assumption made that people don't adapt is often empirically rather unlikely to be met. The potential impact that "many millions more people are projected to be flooded every year due to sea-level rise by the 2080s", reported in the AR4 WG2-SPM (IPCC 2007), for example, is rather unrealistic because this would assume that people continue to live in the coastal zone even though they experience frequent flooding or even permanent inundation (Hinkel 2011b).

Question addressed

What are the impacts of climate change ?

Conditions of applicability

Interaction between the drivers and the study unit can be formally represented as a computational model.

Theoretical assumptions

People affected do not adapt.

Steps taken

1. Selection of climate and socio-economic scenarios 2. Computation of the potential impacts of those scenarios 3. Evaluation of impacts using impact indicators

Results achieved

A list of propositions that map each scenario to an impact. Each proposition is interpreted in the following way: 'When the world evolves according to scenario e and people don't adapt, the impact on will be i'.

Issues involved

Rarely understood that potential impacts will almost certainly not occur because adaptation will take place. E.g., people living in the coastal zone are likely to move away before experiencing permanent flooding.

Example cases from literature

Dasgupta et al. (2007) address the question of what the impacts of sea-level rise are on developing countries are. Impacts are projected for sea-level rise scenarios of 1 to 5 meter by overlaying data on land, population, agriculture, urban extent, wetlands and GDP with the inundation zones of the sea-level rise scenarios. They find that tens of millions of people will be displaced and economic damages will be severe but limited to a couple of countries

External cases (global)

This section is based on the UNEP PROVIA guidance document

Criteria checklist

1. You want to assess vulnerability.
2. Your focus is on impacts.
3. Either no studies on future impacts are available, or available studies are not comprehensive or credible.
4. Impact models are available that can be used to simulate future impacts.
5. Adaptation should not be included in the projection.
Training material