The United Nations Framework Convention on Climate Change (UNFCCC) identifies two responses to climate change: mitigation of climate change by reducing greenhouse-gas emissions and enhancing sinks, and adaptation to the impacts of climate change. Most industrialised countries have committed themselves, as signatories to the UNFCCC and the Kyoto Protocol, to adopting national policies and taking corresponding measures on the mitigation of climate change and to reducing their overall greenhouse-gas emissions (United Nations, 1997). An assessment of current efforts aimed at mitigating climate change, as presented by the Working Group III Fourth Assessment Report (WGIII AR4), Chapter 11 (Barker et al., 2007), shows that current commitments would not lead to a stabilisation of atmospheric greenhouse-gas concentrations. In fact, according to the Working Group I Fourth Assessment Report (WGI AR4), owing to the lag times in the global climate system, no mitigation effort, no matter how rigorous and relentless, will prevent climate change from happening in the next few decades (Christensen et al., 2007; Meehl et al., 2007). Chapter 1 in this volume shows that the first impacts of climate change are already being observed.
Adaptation is therefore unavoidable (Parry et al., 1998). Chapter 17 (see Section 17.2 and Section 17.4) presents examples of adaptations to climate change that are currently being observed, but concludes that there are limits and barriers to effective adaptation. Even if these limits and barriers were to be removed, however, reliance on adaptation alone is likely to lead to a magnitude of climate change in the long run to which effective adaptation is no longer possible or only at very high social, economic and environmental costs. For example, Tol et al. (2006) show what would be the difficulties in adapting to a five-metre rise in sea level in Europe. It is therefore no longer a question of whether to mitigate climate change or to adapt to it. Both adaptation and mitigation are now essential in reducing the expected impacts of climate change on humans and their environment.