G. Gaps in knowledge
28. There are still relevant gaps in currently available knowledge regarding some aspects of mitigation of climate change, especially in developing countries. Additional research addressing those gaps would further reduce uncertainties and thus facilitate decision-making related to mitigation of climate change [TS.14].
Endbox 1: Uncertainty representation
Uncertainty is an inherent feature of any assessment. The fourth assessment report clarifies the uncertainties associated with essential statements.
Fundamental differences between the underlying disciplinary sciences of the three Working Group reports make a common approach impractical. The “likelihood” approach applied in “Climate change 2007, the physical science basis” and the “confidence” and “likelihood” approaches used in “Climate change 2007, impacts, adaptation, and vulnerability” were judged to be inadequate to deal with the specific uncertainties involved in this mitigation report, as here human choices are considered.
In this report a two-dimensional scale is used for the treatment of uncertainty. The scale is based on the expert judgment of the authors of WGIII on the level of concurrence in the literature on a particular finding (level of agreement), and the number and quality of independent sources qualifying under the IPCC rules upon which the finding is based (amount of evidence) (see Table SPM.E.1). This is not a quantitative approach, from which probabilities relating to uncertainty can be derived.
 | High agreement, limited evidence | High agreement, medium evidence | High agreement, much evidence |
Medium agreement, limited evidence | Medium agreement, medium evidence | Medium agreement, much evidence |
Level of agreement (on a particular finding) | Low agreement, limited evidence | Low agreement, medium evidence | Low agreement, much evidence |
|
| Amount of evidence (number and quality of independent sources) |
Table SPM.E.1: Qualitative definition of uncertainty
Because the future is inherently uncertain, scenarios i.e. internally consistent images of different futures - not predictions of the future - have been used extensively in this report.