Abstract
The IPCC’s Fifth Assessment Report (AR5) identifies key risks in a changing climate to inform judgments about danger from climate change and to empower responses. In this article, we introduce the innovations and implications of its approach, which extends analysis across sectors and regions, and consider relevance for future research and assessment. Across key risks in the AR5, we analyze the changing risk levels and potential for risk reduction over the next few decades, an era with some further committed warming, and in the second half of the 21st century and beyond, a longer-term era of climate options determined by the ambition of global mitigation. The key risk assessment underpins the IPCC’s conclusion that increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts. Here, we emphasize central challenges in understanding and communicating risks. These features include the importance of complex interactions in shaping risks, the need for rigorous expert judgment in evaluating risks, and the centrality of values, perceptions, and goals in determining both risks and responses.
Highlights
The IPCC’s Fifth Assessment Report (AR5) identifies key risks in a changing climate to inform judgments about danger from climate change and to empower responses
The integrative WGII AR5 key risk assessment is grounded in a view of climate change as a challenge in understanding, reducing, and managing risks (IPCC 2014c)
In the AR5, risk is defined as Bthe potential for consequences where something of value is at stake and where the outcome is uncertain,^ recognizing that risks will be characterized and perceived differently by people with diverse values (IPCC 2014b)
Summary
The integrative WGII AR5 key risk assessment is grounded in a view of climate change as a challenge in understanding, reducing, and managing risks (IPCC 2014c). Risk emerges from the interaction of hazards (the physical trigger from the climate system), exposure (the people, ecosystems, and assets at stake), and vulnerability (their susceptibility to harm). It can be represented as the probability of hazards occurring multiplied by the consequences that would result. The impacts of climate change do not result from physical climatic hazards They emerge from complex interactions among hazards, exposure, and vulnerability—interactions among climate and societies—through space and time (Oppenheimer et al 2014). Connecting existing climatic consequences to the changing probabilities of such outcomes under various climate and socioeconomic futures can make potential responses tangible. Risk connects the climate challenge to available tools already used to manage risks across contexts and causes, from security and insurance to business and law (e.g., DHS 2011; Lempert et al 2003)
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