Climate Change 2001: Synthesis Report

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5.18 Inertia in the climate, ecological, and socio-economic systems makes adaptation inevitable and already necessary in some cases, and inertia affects the optimal mix of adaptation and mitigation strategies.

5.19 As a result of the time lags and inertias inherent in the Earth system,including its social components, some of the consequences of actions taken, or not taken, will only be felt many years in the future. For example, the differences in the initial trajectories of the various SRES and stabilization scenarios are small, but the outcomes in terms of the climate in the year 2100 are large. The choice of development path has consequences at all the affected time scales; thus, long-term total costs and benefits may differ considerably from short-term ones.

WGIII TAR Section 8.4.2
5.20 In the presence of inertia, well-founded actions to adapt to or mitigate climate change are more effective, and under some circumstances may be cheaper, if taken earlier rather than later. Time lags provide a breathing space between emissions and impacts, thus allowing time for planned adaptation. The inertia of technology development and capital stock replacement is an important argument for gradual mitigation. The essential point of inertia in economic structures and processes is that deviation from any given trend incurs costs, and these costs rise with the speed of deviations (e.g., the costs of early retirement of carbon-intensive facilities). Earlier mitigation action may reduce the risk of incurring severe lasting or irreversible impacts, while reducing the need for more rapid mitigation later.Accelerated action may help to drive down the costs of mitigation and adaptation in the long term by accelerating technology development and the early realization of benefits currently obscured by market imperfections. Abatement over the next few years is economically valuable if there is a significant probability of having to stay below ceilings that would otherwise be reached within the characteristic time scales of the systems producing greenhouse gases. Climate change mitigation decisions depend on the interplay of inertia and uncertainty, resulting in a sequential decision-making process. Foresight and early adaptation will be most advantageous in sectors with long-lived infrastructure, such as dams and bridges, and large social inertia, such as misallocated property rights. Anticipatory adaptive action can be very cost-effective if the anticipated trend materializes.

WGII TAR Sections 1.3.4 & 2.7.1, WGIII TAR Chapter 2, WGIII TAR Sections 10.1 & 10.4.2-3, & WGIII TAR Table 10.7
5.21 The existence of time lags, inertia, and irreversibility in the Earth system means that a mitigation action or technology development can have different outcomes, depending on when it is taken. For example, in one model analysis of the hypothetical effect of reducing anthropogenic greenhouse gas emissions to zero in the year 1995, on sea-level rise during the 21st century in the Pacific, showed that the sea-level rise that would inevitably occur due to warming incurred to 1995 (5 to 12 cm) would be substantially less than if the same emission reduction occurred in the year 2020 (14 to 32 cm). This demonstrates the increasing commitment to future sea-level rise due to past and present emissions, and the effect of delaying the hypothetical emissions reduction.

WGII TAR Sections 2.7.1 & 17.2.1
5.22 Technological inertia in less developed countries can be reduced through "leapfrogging" (i.e., adopting anticipative strategies to avoid the problems faced today by industrial societies). It cannot be assumed that developing countries will automatically follow the past development paths of industrialized countries. For example, some developing countries have bypassed land-lines for communication, and proceeded directly to mobile phones. Developing countries could avoid the past energy-inefficient practices of developed countries by adopting technologies that use energy in a more sustainable way, recycling more wastes and products, and handling residual wastes in a more acceptable manner. This may be easier to achieve in new infrastructure and energy systems in developing countries since large investments are needed in any case. Transfer of technology between countries and regions can reduce technological inertia. WGII TAR Chapter 2, WGIII TAR Section 10.3.3, SRES Section, & SRTT SPM

Inertia and uncertainty in the climate, ecological, and socio-economic systems imply that safety margins should be considered in setting strategies, targets, and time tables for avoiding dangerous levels of interference in the climate system. Stabilization target levels of, for instance, atmospheric CO2 concentration, temperature, or sea level may be affected by:

  • The inertia of the climate system, which will cause climate change to continue for a period after mitigation actions are implemented
  • Uncertainty regarding the location of possible thresholds of irreversible change and the behavior of the system in their vicinity
  • The time lags between adoption of mitigation goals and their achievement.

Similarly, adaptation is affected by time lags involved in identifying climate change impacts, developing effective adaptation strategies, and implementing adaptive measures. Hedging strategies and sequential decision making (iterative action, assessment, and revised action) may be appropriate responses to the combination of inertia and uncertainty. Inertia has different consequences for adaptation than for mitigation, with adaptation being primarily oriented to address localized impacts of climate change, while mitigation aims to address the impacts on the climate system. Both issues involve time lags and inertia, with inertia suggesting a generally greater sense of urgency for mitigation.

WGII TAR Section 2.7.1 & WGIII TAR Sections
5.24 The pervasiveness of inertia and the possibility of irreversibility in the interacting climate, ecological, and socio-economic systems are major reasons why anticipatory adaptation and mitigation actions are beneficial. A number of opportunities to exercise adaptation and mitigation options may be lost if action is delayed.


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