Addressing the limits to adaptation across four damage–response systems

• Adaptation limits are reached when climate damages overwhelm adaptation responses.
• Environmental and human–response systems interact to form damage–response systems.
• The pathways of adaptation degradation and failure can be gradual or sudden.
• Four archetypical damage–response systems are developed, which could apply to different sectors.
• Policy options include investment in more, better, or transformational adaptation.

Our ability to adapt to climate change is not boundless, and previous modeling efforts show that future policy decisions about climate change are affected when adaptation limits are exceeded. Adaptation limits are delineated by capacity thresholds, after which climate damages begin to overwhelm the adaptation response and net adaptation goes negative. The levels of such thresholds depend on the complex interaction of different environmental (climatic and ecological) and human response (technological and societal) systems. In this paper, the interactions among these sub-systems are explored and four novel archetypical climate damage and adaptation response systems are developed. These damage–response systems can be described by the level of their adaptation limits thresholds, the pathways of adaptation capacity degradation and failure, and the recoverability or permanence of such climate losses once the adaptation limits have been surpassed. Policy options upon reaching the limits to adaptation include investment in more of the same technology, implementation of new and more effective adaptation, or transformational adaptation that allows the damage–response system to become more resilient. Attention is drawn to the need for greater understanding of the uncertainties of adaptation limits, how to raise the effective capacities and lifetime ranges of adaptation (and thus delay adaptation failure), and what policy options exist when adaptation limits are breached.