1.2.3.2 Adaptation and mitigation
Adaptation and mitigation can be complementary, substitutable or independent of each other (see IPCC, 2007b, Chapter 18). If complementary, adaptation reduces the costs of climate change impacts and thus reduces the benefits of mitigation. Although adaptation and mitigation may be substitutable up to a certain point, they are never perfect substitutes for each other since mitigation will always be required to avoid ‘dangerous’ and irreversible changes to the climate system. Irrespective of the scale of the mitigation measures that are implemented in the next 10–20 years, adaptation measures will still be required due to the inertia in the climate system. As reported in IPCC, 2007b, Chapter 19 (and also noted in Stern (2006)), changes in the climate are already causing setbacks to economic and social development in some developing countries with temperature increases of less than 1°C. Unabated climate change would increase the risks and costs very substantially (IPCC, 2007b, Chapter 19). Both adaptation and mitigation depend on capital assets, including social capital, and both affect capital vulnerability and GHG emissions (see Chapter 2, Section 2.5.2). Through this mutual dependence, both are tied to sustainable development (see Sections 2.5, 11.8 and 11.9, 12.2 and 12.3).
The stabilization of GHG concentrations and, in particular, of the main greenhouse gas, CO2, requires substantial emission reductions, well beyond those built into existing agreements such as the Kyoto Protocol. The timing and rate of these reductions depend on the level of the climate goal chosen (see Chapter 3.3.5.1).
1.2.3.3 Inertia
Inertia in both the climate and socio-economic systems would need to be taken into account when mitigation actions are being considered. Mitigation actions aimed at specific climate goals would need to factor in the response times of the climate system, including those of the carbon cycle, atmosphere and oceans. A large part of the atmospheric response to radiative forcing occurs on decadal time scales, but a substantial component is linked to the century time scales of the oceanic response to the same forcing changes (Meehl et al., 2007). Once GHG concentrations are stabilized global mean temperature would very likely stabilize within a few decades, although a further slight increase may still occur over several centuries (Meehl et al., 2007). The rise in sea level, however, would continue for many centuries after GHG stabilization due to both ongoing heat uptake by the oceans and the long time scale of ice sheet response to warming (Meehl et al., 2007). The time scales for mitigation are linked to technological, social, economic, demographic and political factors. Inertia is a characteristic of the energy system with its long-life infrastructures, and this inertia is highly relevant to how fast GHG concentrations can be stabilized (Chapter 11.6.5). Adaptation measures similarly exhibit a range of time scales, and there can be substantial lead times required before measures can be implemented and subsequently take effect, particularly when it involves infrastructure (IPCC, 2007b, Chapter 17).
The consequence of inertia in both the climate and socio-economic systems is that benefits from mitigation actions initiated now – in the short term – would lead to significant changes in the climate being avoided several decades further on. This means that mitigation actions need to be implemented in the short term in order to have medium- and long-term benefits and to avoid the lock in of carbon intensive technologies (Chapter 11.6.5).