be “surprises” in the climate system requires careful monitoring of climate conditions, improved models for projecting changes, and the interpretation and synthesis of scientific data using novel analysis techniques. In light of the importance of actionable information about the occurrence and impacts of abrupt changes, it is the Committee’s judgment that action is urgently needed to improve society’s ability to anticipate abrupt climate changes and impacts.

To address these needs the Committee recommends development of an Abrupt Change Early Warning System (ACEWS). Surprises in the climate system are inevitable: an early warning system could allow for the prediction and possible mitigation of such changes before their societal impacts are severe. Identifying key vulnerabilities can help guide efforts to increase resiliency and avoid large damages from abrupt change in the climate system, or in abrupt impacts of gradual changes in the climate system, and facilitate more informed decisions on the proper balance between mitigation and adaptation. With adequate scientific monitoring and study of these potential changes to the climate system, the probability that society can anticipate future abrupt climate changes and impacts will be substantially increased.

An ACEWS would be part of an overall risk management strategy, providing required information for hazard identification and risk assessment. In general, an ACEWS system would (1) identify and quantify social and natural vulnerabilities and ensure longterm, stable observations of key environmental and economic parameters through enhanced and targeted monitoring; (2) integrate new knowledge into numerical models for enhanced understanding and predictive capability; and (3) synthesize new learning and advance the understanding of the Earth system, taking advantage of collaborations and new analysis tools. The improved information could help identify vulnerabilities to assist in tailoring risk mitigation and preparedness efforts to ensure warnings result in the appropriate protective actions, with the ultimate goal to preempt catastrophes. Planning an ACEWS would benefit from leveraging the experience and knowledge gained as part of existing early warning programs such as the National Integrated Drought Information System (NIDIS) and Famine Early Warning System Network (FEWS NET). The Committee described several important aspects of a strategy to provide an effective Abrupt Change Early Warning System (ACEWS):

  • Monitor key variables of abrupt change: Monitoring for an ACEWS should expand upon existing monitoring networks, protect and/or augment important networks that are currently in place, and develop new ones as needed (examples of specific monitoring needs are listed in Table S.1).
  • Modeling to project future abrupt changes: A successful and adaptive ACEWS must consistently iterate between data collection, model testing and improve-


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