NERC-NSF-GEO Assessing Decadal Variability of Sea Ice (ADVIce)

This award was made possible through the NSF/GEO-UKRI/NERC lead agency opportunity. This is a project jointly funded by the National Science (NSF) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Opportunity. This Lead Agency Opportunity allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries. Decision-makers and stakeholders rely on an accurate understanding of sea ice at both poles. Arctic sea-ice cover declined rapidly for several decades but has been relatively steady for roughly the past twenty years, while Antarctic sea ice, which was broadly stable or slightly increasing from 1979 to 2015, has contracted sharply since 2016. These shifts are important because polar sea ice affects ecosystems, ocean circulation, and human activity. Better near-term projections of Arctic sea ice can inform maritime transport, U.S. national security, and commercial investment in a rapidly changing region, while improved understanding of Antarctic sea ice is important for assessing trends in the Southern Ocean. This project will improve understanding of why polar sea ice changes over decades and how future changes can be projected more reliably. This project also support U.S. workforce development by training an early-career postdoctoral researcher in large-ensemble analysis. On decadal timescales, sea-ice evolution reflects both internal variability and responses to external forcings, including volcanic eruptions, greenhouse gases, and aerosols, but the relative roles of these factors and the mechanisms involved remain poorly quantified at both poles. This project will address this problem through three linked goals: identifying the mechanisms and forcings that drive decadal sea-ice variability and evaluating how well they are represented in Earth system models; diagnosing the likelihood, characteristics, and drivers of surge and slowdown events in sea-ice loss, defined as multiyear periods when sea ice is lost substantially faster or slower than its long-term trend; and producing more precise near-term projections of Arctic and Antarctic sea ice. The project will apply Low Frequency Component Analysis to century-long observational reconstructions and model large ensembles; extend existing large-ensemble historical simulations to the present using updated forcings, covering the period of the recent Arctic slowdown and Antarctic sea-ice decline; use single-forcing large ensembles to separate internally generated variability from externally forced variability; and statistically adjust projections using the observed phase and magnitude of decadal variability, including the first application of this approach to Antarctic sea ice. This project will provide new metrics for evaluating models and improved, observationally constrained near-term projections of sea ice at both poles. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.