A new assessment of regional sea ice changes from a revised passive microwave climate data record of sea ice extent and area

Sea ice extent has been decreasing substantially in the Arctic, with record or near-record low extents in many recent years starting in 2007. In the Antarctic, inter-annual variability has dominated with record highs being followed shortly after by record low extents. There are also substantial differences in regional trends and variability in both hemispheres. To date, regional characterization has largely been based on somewhat arbitrary regional definitions that were derived many years ago. Here we present updated regional sea ice statistics based on newly derived regional maps based on International Hydrographic Organization definitions, modified for better applicability to sea ice. Unlike previous region maps, the new version is easily and consistently adaptable and extendable to different projections and grid resolutions, and is fully-documented with source provenance provided. This region map is applied to a new version of the NOAA/NSIDC Sea Ice Concentration Climate Data Record (CDR), based on NASA algorithms. This version contains several new features including updated concentration algorithms, full provenance of the processing and source data, spatial and temporal interpolation to fill gaps and yield complete daily fields starting in November 1978. Comparisons show good agreement with the heritage NASA product, while providing ancillary information such as data quality and better provenance that better meets open science standards. Trends and climatologies presented through 2020 for the Antarctic and Arctic, update previous analysis and provide new insights into the changing character of the ice cover. For example, the Bering Sea has been one region with an increasing trend in the winter, but winter 2017-2018 and 2018-2019 saw record low extents with little or no ice during much of the winter season. The new region map and updated sea ice CDR provide a new high-quality observational record of sea ice changes and will be useful for comparison with climate models.