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A mechanism for the Arctic sea ice spring predictability barrier

Key Findings

  • Summer sea ice predictability is limited in winter months by synoptically-driven sea-ice mass export and negative feedbacks from sea-ice growth.
  • The spring predictability barrier results from a sharp increase in predictability at melt onset, when ice-albedo feedbacks act to enhance and persist the preexisting export-generated mass anomaly.
  • The predictability barrier is expected to shift earlier under Arctic warming due to shifts in melt onset timing.
  • These results imply that ice thickness observations collected after melt onset are particularly critical for summer Arctic sea-ice predictions.

Mitchell Bushuk, Michael Winton, David Bonan, Edward Blanchard-Wrigglesworth, Thomas Delworth. Geophysical Research Letters. DOI: 10.1029/2020GL088335

Observations over the past 40 years have documented a significant decline in Arctic sea-ice extent and thickness. These rapid changes and their implications for Northern communities, shipping industries, wildlife, fisheries, and natural resource industries have created an emerging operational need for regional summer sea-ice predictions.

How far in advance can accurate predictions of regional summer sea ice be made? Recent work has shown evidence for an Arctic sea ice spring predictability barrier, which may fundamentally limit the accuracy of predictions made before May. However, the physical mechanism for this barrier has remained elusive. This work reveals a mechanism for the Arctic sea ice spring predictability barrier, examines the evolution of the predictability barrier under climate change, and describes implications for future Arctic seasonal prediction systems.

This works finds that summer sea-ice predictability is limited in winter months by synoptically-driven sea-ice mass export and negative feedbacks from sea-ice growth. The spring predictability barrier results from a sharp increase in predictability at melt onset, when ice-albedo feedbacks act to enhance and persist the preexisting export-generated mass anomaly. The predictability barrier is expected to shift earlier under Arctic warming due to shifts in melt onset timing. These results imply that ice thickness observations collected after melt onset are particularly critical for summer Arctic sea-ice predictions.

The mechanism for the Arctic sea ice spring predictability barrier was investigated using a sea-ice mass budget analysis, based on daily data from large-ensemble experiments performed with two global climate models. The mass budget analysis allows for a process-based attribution of summer sea-ice predictability. The authors considered the relative roles of ice growth and melt (thermodynamics) and ice flow (dynamics) in controlling summer sea ice. They found that predictability is limited by ice motion and growth in winter, and increases rapidly in spring due to melt processes. This analysis reveals a mechanism for the spring predictability barrier, in which the timing of the barrier is set by the spring onset of sea ice melt.

Regional summer sea ice predictions could potentially be useful to a broad group of stakeholders, including northern communities and wildlife, resource industries, commercial shipping, fisheries, tourism, and nations with claims to Arctic sovereignty. This study answers the key question of how far in advance we can expect to make skillful predictions of summer Arctic sea ice. The authors also identify satellite sea ice thickness measurements, collected after melt onset, as a key observational need for future seasonal prediction systems.


This figure summarizes the key aspects of the proposed mechanism for the spring predictability barrier, showing the evolution of sea ice mass (SIM) anomalies (magenta curves) from October 1 through to the following summer. Ice export (green curves) is the dominant driver of regional SIM variability in fall, winter, and spring seasons. These export-generated variations are partially opposed by the negative ice growth-thickness feedback (black curves). Export-driven mass anomalies represent the accumulated effect of synoptic events which are inherently unpredictable beyond a few weeks. Consequently, summer SIA predictability increases over the winter months, but at a relatively modest rate. The predictability barrier timing is characterized by a rapid increase in predictability due to melt-generated SIM anomalies (red curves), beginning at the time of melt onset. These melt-driven anomalies act to “lock in” the pre-existing export-driven mass anomaly via positive ice-albedo feedbacks, which enhance the mass anomaly. This anomaly persists through the melt season, creating a corresponding late-summer SIA anomaly (cyan curves).

 

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