Very few studies have yet assessed the feasibility of adaptation to climate change on a global scale, and there are limited assessments of the feasibility of adaptation even at the local scale in a number of sectors for many regions. Where adaptation is physically feasible, the issue is not only whether adaptation will reduce the impacts, but also what is the cost of that adaptation – is it economically feasible – and whether other barriers to adaptation make it unlikely that the adaptation will be implemented. A number of studies estimate the costs of adaptation, often by assuming that there are no physical or social barriers to the adaptation, and have come up with very large cost estimates running into billions of dollars annually. In all sectors, the adaptation challenges for a global warming of 4°C is significantly, or much, greater than the challenge for a mean global warming of 2°C above pre-industrial levels, with an expectation that a far larger number of limits to adaptation would be exceeded in a 4°C warmer world.
It is physically feasible to adapt to high levels of coastal and river flooding, but only low levels of ecosystem and biodiversity change. In previous work, AVOID has found that mitigation can be said to ‘buy’ more than 30 years of time to adapt to a particular level of climate change impacts (Price et al 2013). This means that investment in adaptation could take place over a much longer period: adaptation could be either cheaper, or more effective (or both) if it is implemented in combination with mitigation. The findings of this report are in line with IPCC AR5, but provide more detail or extend the information available, especially when new material has been published. The report approaches adaptation in some sectors (particularly coasts and ecosystems) from a methodological angle which complements, yet is still in line with, information provided in AR5.
The findings of this report are consistent with and complement those of the UNEP adaptation gap report (UNEP 2014), which does not consider climate changes beyond 2050 and therefore does not address potential warming above around 2°C above pre-industrial levels. However, it estimates that adaptation costs are already doubled by 2050 on pathways to 4°C warming by the end of the century compared with pathways that limit warming to 2°C. The UNEP report highlights limits to adaptation such as those found in ecosystems, and barriers to adaptation in human systems caused by lack of funding or knowledge transfer. It also finds that global scale estimates of adaptation costs such as those reported in this study are likely to be underestimated by a factor of 4 or 5 due to the (necessarily) incomplete nature of the estimates.