Uncertainty in modeled Arctic sea ice volume

TLDR

The PIOMAS Arctic sea ice volume record is characterized by uncertainty. The study examines PIOMAS ice volume uncertainties and trends in the context of climate change attribution and record minima declaration. The authors used in‑situ ice‑thickness measurements, ICESat retrievals, and model sensitivity studies to estimate October Arctic ice‑volume uncertainty (1.35×10³ km³) and trend uncertainty (1.0×10³ km³ decade⁻¹). The study finds a conservative trend of –2.8×10³ km³ decade⁻¹, with PIOMAS ice‑thickness estimates agreeing with ICESat data where available but overestimating thin ice and underestimating thick ice, leading to a smaller downward trend; preindustrial simulations show no comparable trends, and the 2010 September minimum is a statistically significant new record.

Abstract

[1] Uncertainty in the Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) Arctic sea ice volume record is characterized. A range of observations and approaches, including in situ ice thickness measurements, ICESat retrieved ice thickness, and model sensitivity studies, yields a conservative estimate for October Arctic ice volume uncertainty of 1.35 × 103 km3 and an uncertainty of the ice volume trend over the 1979–2010 period of 1.0 × 103 km3 decade–1. A conservative estimate of the trend over this period is −2.8 × 103 km3 decade–1. PIOMAS ice thickness estimates agree well with ICESat ice thickness retrievals (<0.1 m mean difference) for the area for which submarine data are available, while difference outside this area are larger. PIOMAS spatial thickness patterns agree well with ICESat thickness estimates with pattern correlations of above 0.8. PIOMAS appears to overestimate thin ice thickness and underestimate thick ice, yielding a smaller downward trend than apparent in reconstructions from observations. PIOMAS ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima. The distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the PIOMAS retrospective, even when the trend uncertainty is accounted for. Attempts to label September minima as new record lows are sensitive to modeling error. However, the September 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record.