Summary

An understanding of Arctic sea ice is important because the Arctic plays a role in influencing not only the global climate system, but also the global economic system through changes in marine access and natural resource development (Box S.1). Recent dramatic changes in the thickness and extent of the Arctic sea ice cover, which can be linked to the warming climate, are well documented. These changes affect a growing community of diverse stakeholders, including local populations (e.g., indigenous populations), natural resource industries, fishing communities, commercial shippers, marine tourism operators, national security organizations, regulatory agencies, and the scientific research community. Accompanying this growing interest is an urgent demand to increase the pace and scope of the advancements in predictive capabilities. Added pressure comes with the reality of the limited resources (e.g., funding and infrastructure) available to enable continued improvement of Arctic sea ice prediction and the likelihood that, in the face of continued warming, the Arctic will remain a dynamic environment well into the 21st century.

As tasked by the National Aeronautics and Space Administration, the Office of Naval Research, and the intelligence community, the committee convened a

BOX S.1
KEY SCIENCE QUESTIONS

• What are the implications of the recent dramatic shifts in the Arctic from predominantly multiyear ice to first-year ice, and how will the associated complexities of this regime shift affect sea ice variability and predictability?

• In a rapidly changing Arctic regime, how will forcings and couplings between the various components of the ocean, atmosphere, cryosphere, seafloor, and land systems modify or influence the processes governing the characteristics of the sea ice cover?

• What are the impacts of extreme events and feedback mechanisms on Arctic sea ice evolution and our ability to predict it?

• How will changing Arctic sea ice characteristics and dynamics affect stakeholders on a variety of timescales, including prediction requirements?



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Summary An understanding of Arctic sea ice is scientific research community. important because the Arctic plays a role in Accompanying this growing interest is an influencing not only the global climate urgent demand to increase the pace and system, but also the global economic system scope of the advancements in predictive through changes in marine access and capabilities. Added pressure comes with the natural resource development (Box S.1). reality of the limited resources (e.g., funding Recent dramatic changes in the thickness and infrastructure) available to enable and extent of the Arctic sea ice cover, which continued improvement of Arctic sea ice can be linked to the warming climate, are prediction and the likelihood that, in the well documented. These changes affect a face of continued warming, the Arctic will growing community of diverse stakeholders, remain a dynamic environment well into the including local populations (e.g., indigenous 21st century. populations), natural resource industries, As tasked by the National Aeronautics fishing communities, commercial shippers, and Space Administration, the Office of marine tourism operators, national security Naval Research, and the intelligence organizations, regulatory agencies, and the community, the committee convened a BOX S.1 KEY SCIENCE QUESTIONS What are the implications of the recent dramatic shifts in the Arctic from predominantly multiyear ice to first-year ice, and how will the associated complexities of this regime shift affect sea ice variability and predictability? In a rapidly changing Arctic regime, how will forcings and couplings between the various components of the ocean, atmosphere, cryosphere, seafloor, and land systems modify or influence the processes governing the characteristics of the sea ice cover? What are the impacts of extreme events and feedback mechanisms on Arctic sea ice evolution and our ability to predict it? How will changing Arctic sea ice characteristics and dynamics affect stakeholders on a variety of timescales, including prediction requirements? 1

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2 Seasonal to Decadal Predictions of Arctic Sea Ice: Challenges and Strategies workshop with the goal of exploring current promising avenues in addressing the major challenges in sea ice prediction and most pressing needs. identifying new methods, observations, and technologies that might advance seasonal to This deliberately integrative approach decadal sea ice predictive capabilities would not only help address the challenges through improved understanding of the identified in Chapter 2, but is also necessary Arctic system. The content of this report is to effectively implement many of the largely informed by the discussions held strategies laid out in Chapter 3. during the workshop and is augmented by In this spirit, there are several key the committee's deliberations. overarching challenges, not unique to the A key theme resonating throughout the topic of sea ice prediction, that hinder report is the importance of a coordinated advancements in our predictive capabilities: and integrative approach to advance sea ice prediction. In fact, fundamental to the Treating the Arctic sea ice cover not in success of the workshop was a purposeful isolation, but as an integral part of the approach taken to foster a dialogue between complex Arctic system which, in turn, polar researchers, agency representatives, is an integral element of the global and end users. The committee concludes system; that there is a need for this dialogue to be Understanding how the recent regime sustained well beyond the confines of the shift in the Arctic sea ice cover from workshop format. A committed and predominantly multiyear to first-year deliberately integrative approach, founded ice affects the processes governing the on a sustained and coordinated conversation atmosphere-sea ice-ocean system, the among the user, modeling, and observation power of statistical prediction communities, is necessary to: methods, the validity of current numerical models and their Identify and address key gaps in our parameterizations, and observational fundamental understanding of the requirements, including instrument Arctic environment and its connection design; and to the global climate system; Clearly defining the needs of the Balance high-priority stakeholder growing number of stakeholders, many needs against realistic predictive with additional and more sophisticated capabilities; requirements, and balancing these Foster coordinated support of this needs against realistic predictive work within the private and public capabilities. sectors; Provide guidance in allocation of The detailed needs of the diverse resources to support the most stakeholder community are reflected in an equally diverse set of temporal and spatial

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Summary 3 requirements. Likewise, many of the needs at these longer timescales is to improve the and challenges associated with sea ice ability to simulate realistic forcings by the prediction depend on the timescales of atmosphere and ocean using coupled interest. At shorter timescales (seasonal to climate models at decadal timescales, and to interannual), predictive capability is thought identify the model variable and/or processes to reside primarily in an adequate that contribute to unrealistic simulations. knowledge of the initial ice-ocean state, although admittedly little information exists In light of these challenges and while on what constitutes an "adequate recognizing that there are limitations in knowledge." Challenges on the seasonal current modeling and observational timescales include: techniques, the committee offers possible strategies to significantly enhance our Understanding the relative strengths and understanding and predictions of the Arctic weaknesses of the different existing sea ice cover over seasonal to decadal approaches used to generate seasonal ice timescales: forecasts (statistical algorithms, coupled ice-ocean models driven by prescribed A systematic evaluation of the existing atmospheric forcing, and coupled seasonal prediction capabilities to atmosphere-ocean-ice models); establish baseline expectations for Establishing specific key observational predictive power and to set the stage data requirements necessary for defining for advances in predictive capability; the initial ice-ocean state for seasonal sea A highly coordinated and integrated ice predictions; and process-based study of seasonal sea ice Providing access to observational data at focused on understanding the impact fast turnaround times. of the increasing predominance of younger, first-year ice on sea ice At longer (decadal and greater) predictions and offering an timescales, the role of trends in external opportunity to identify, develop, and forcings (e.g., increasing greenhouse gases) test instruments and observational and of factors that control the forcings is platforms; likely to provide some predictive potential Inform research investments related to because they account for increasingly large observational needs (e.g., observation fractions of the change from present sea ice types, locations, and coverage) in conditions. A critical point of uncertainty support of sea ice modeling and remains regarding the timescale at which a prediction by conducting an organized transition occurs between these two regimes, set of model sensitivity studies. and there is likely to be an intermediate Enhance the capabilities of numerical timescale for which the potential models through a coordinated predictability is low. The primary challenge experiment with multiple models to (a)

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4 Seasonal to Decadal Predictions of Arctic Sea Ice: Challenges and Strategies identify which variables and processes These strategies are offered as guidance are critical to simulating a realistic ice toward facilitating a transformative change cover, (b) determine the sources of in (1) our understanding of Arctic sea ice climate model drift, and (c) guide predictability on seasonal to decadal decisions regarding high-priority timescales and (2) our collective ability to model development needs and the realize and effectively communicate useful expansion of models to include predictive power. The rate of advancement additional capabilities and variables of in sea ice predictions will likely be interest to stakeholders; and determined by the extent to which the broad Create a centralized information hub user, modeling, and observational that facilitates the timely access to communities can achieve a sustained, observational and modeling results integrative approach to refining and and encourages sustained implementing these and other strategies. communication among stakeholders.