HECC refers to extreme projections with global annual temperature increases of over 4°C. The authors analyse whether HECC scenarios are used in the adaptation decision-making of stakeholders who will tackle the potential problem. They also explore whether the adaptation actions being considered are pertinent only to future climate change or whether other drivers and information types are used in decision-making (including non-climate drivers). Furthermore, they address the role of knowledge uncertainty in adaptation decision-making.

Decision-makers perceive HECC as having a low probability of occurrence and so they do not directly account for HECC within existing actions to address climate change. Such actions focus on incremental rather than transformative solutions in which non-climate drivers are at least as important, and in many cases more important, than climate change alone. This reflects the need to accommodate multiple concerns and low-risk options (i.e. incremental change).

Uncertainty in climate change information is not a significant barrier to decision-making and stakeholders indicated little need for more climate information in support of adaptation decision-making. There is, however, an identified need for more information about the implications of particular sectoral and cross-sectoral impacts under HECC scenarios. The outcomes of this study provide evidence to assist in contextualizing climate change information by creating usable, cross-sectoral, decision-centred information.

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