IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

18.1.2 Differences, similarities and complementarities between adaptation and mitigation

The TAR used the following definitions of climate change mitigation and adaptation.

  • Mitigation: An anthropogenic intervention to reduce the sources or enhance the sinks of greenhouse gases (IPCC, 2001a).
  • Adaptation: Adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects, which moderates harm or exploits beneficial opportunities (IPCC, 2001a).

It follows from these definitions that mitigation reduces all impacts (positive and negative) of climate change and thus reduces the adaptation challenge, whereas adaptation is selective; it can take advantage of positive impacts and reduce negative ones (Goklany, 2005).

The two options are implemented on the same local or regional scale, and may be motivated by local and regional priorities and interests, as well as global concerns. Mitigation has global benefits (ancillary benefits might be realised at the local/regional level), although effective mitigation needs to involve a sufficient number of major greenhouse-gas emitters to foreclose leakage. Adaptation typically works on the scale of an impacted system, which is regional at best, but mostly local (although some adaptation might result in spill-overs across national boundaries, for example by changing international commodity prices in agricultural or forest-product markets). Expressed as CO2-equivalents, emissions reductions achieved by different mitigation actions can be compared and if the costs of implementing the actions are known, their cost-effectiveness can be determined and compared (Moomaw et al., 2001). The benefits of adaptation are more difficult to express in a single metric, impeding comparisons between adaptation efforts. Moreover, as a result of the predominantly local or regional effect of adaptation, benefits of adaptation will be valued differently depending on the social, economic and political contexts within which they occur (see Chapter 17).

The benefits of mitigation carried out today will be evidenced in several decades because of the long residence time of greenhouse gases in the atmosphere (ancillary benefits such as reduced air pollution are possible in the near term), whereas many adaptation measures would be effective immediately and yield benefits by reducing vulnerability to climate variability. As climate change continues, the benefits of adaptation (i.e., avoided damage) will increase over time. Thus there is a delay between incurring the costs of mitigation and realising its benefits from smaller climate change, while the time span between expenditures and returns of adaptation is usually much shorter. This difference is augmented in analyses adopting positive discount rates. These asymmetries have led to a situation whereby the initiative for mitigation has tended to stem from international agreements and ensuing national public policies (sometimes supplemented by community-based or private-sector initiatives), whereas the bulk of adaptation actions have historically been motivated by the self-interest of affected private actors and communities, possibly facilitated by public policies.

There are a number of ways in which adaptation and mitigation are related at different levels of decision-making. Mitigation efforts can foster adaptive capacity if they eliminate market failures and distortions, as well as perverse subsidies that prevent actors from making decisions on the basis of the true social costs of the available options. At a highly aggregated scale, mitigation expenditures appear to divert social or private resources and reduce the funds available for adaptation, but in reality the actors and budgets involved are different. Both options change relative prices, which can lead to slight adjustments in consumption and investment patterns and thus to changes in the affected economy’s development pathway, but direct trade-offs are rare. The implications of adaptation can be both positive and negative for mitigation. For example, afforestation that is part of a regional adaptation strategy also makes a positive contribution to mitigation. In contrast, adaptation actions that require increased energy use from carbon-emitting sources (e.g., indoor cooling) would affect mitigation efforts negatively.