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What is meant by uncertainty?

Adapting to climate change poses challenges to decision-makers who need to decide now whether and how to adapt activities, systems and sectors, at all geographical scales, to a changing climate.

Uncertainty is not exclusive to climate change and adaptation. Many other scientific and policy fields are confronted with a wide range of uncertainties in their work. Uncertainty is a complex concept that can be described in multiple ways, and its consideration in decision support has evolved over time. Some relevant descriptions of uncertainty include:

  • A state of incomplete knowledge that can result from a lack of information or from disagreement about what is known or even knowable. It may have many types of sources, from imprecision in the data to ambiguously defined concepts or terminology, or uncertain projections of human behaviour. Uncertainty can therefore be represented by quantitative measures (e.g. a probability density function) or by qualitative statements (e.g. reflecting the judgment of a team of experts) (IPCC AR5 2014).
  • The degree of confidence that a decision-maker has about possible outcomes of specific decisions and/or probabilities of these outcomes. Reasons behind this lack of confidence might include a judgement of the information as incomplete, blurred, inaccurate, unreliable, inconclusive, or potentially false (Refsgaard et al. 2007).

What are the main sources of uncertainty in adaptation planning?

A wide range of information sources and data can be used to support adaptation planning. Information on past and projected climate is one among several types of information that is used in support of adaptation planning. Other types typically include information that is derived from, for example: impact assessment models, past experience of dealing with climate variability and change, socioeconomic conditions, policy context, market context (for economic actors) and the expectation of changes in these contexts.

Any information related to the future conditions of natural and social systems has uncertainties that users of this information should be aware of. Some of the main sources of uncertainty related to climate change impacts and adaptation include (EEA 2017):

  • Measurement errors resulting from imperfect observational instruments (e.g. rain gauges) and/or data processing (e.g. algorithms for estimating surface temperature based on satellite data);
  • Aggregation errors resulting from incomplete temporal and/or spatial data coverage;
  • Natural variability resulting from unpredictable natural processes within the climate system (internal climate variability; e.g. atmospheric and oceanic variability), influencing the climate system (e.g. future volcanic eruptions) and/or within climate-sensitive environmental and social systems (e.g. ecosystem dynamics);
  • Model limitations (of climate and climate impact models) resulting from the limited resolution of models (e.g. hampering the explicit resolution of cloud physics), an incomplete understanding of individual Earth system components (e.g. dynamic ice sheet processes) or their interactions and feedbacks (e.g. climate–carbon cycle feedbacks), and/or an incomplete understanding of the environmental or social system under consideration (e.g. demographic development in flood risk zones);
  • Future emissions trajectories (of greenhouse gases and aerosols) determine the magnitude and rate of future climate change. Future emission levels depend on demographic, economic and technological development, as well as on international agreements for climate change mitigation (in particular under the UNFCCC);
  • Future development of non-climatic (socio-economic, demographic, technological and environmental) factors determines how a given change in climate affects the environment and society;
  • Future changes in societal preferences and political priorities determine the importance attached to a given climate impact (e.g. a local or regional loss of biodiversity).

Why it is important to consider uncertainty in decision-making?

Adaptation to climate change presents a complex methodological challenge. It calls for individuals to make decisions with potentially very long-term consequences on the basis of incomplete knowledge and/or uncertain information about future changes.

Some reasons why it is important to consider uncertainty in adaptation decision-making include (Street and Nilsson 2014):

  • Uncertainty is inherent. Consideration of uncertainty is an essential element of decision-making as it is inherent in all evidence and in all decisions. It is an integral part of supportive data and information, especially but not only in that related to the future. Appropriately integrating the associated uncertainties as part of the evidence provides a better understanding of that evidence and can enhance its utility within decision-making processes;
  • More relevant and robust decision-making. Recognising the nature and characteristics of uncertainty and reflecting these in how the associated evidence is used are crucial to making better informed, more relevant and more robust decisions. By acknowledging and considering uncertainties, rather than expecting readily identifiable and deterministic outcomes, the uncertainties become more manageable. As a result, it becomes possible to formulate coherent decisions and policies;
  • Minimise the potential for maladaptation. Not ‘sufficiently’ including uncertainties increases the likelihood that the action taken will be inadequate, inappropriate or increase vulnerability. There is an increased likelihood of maladaptation when neglecting uncertainties in the knowledge base;
  • Ignoring uncertainty conceals risks. Ignoring uncertainty can undermine effective risk management as the risks that would result from including uncertainty are simply ignored and not considered in actions to be taken.



Other main topics:

2. How are uncertainties communicated?

3. How to factor in uncertainty?

Resources for further reading