Comparison of Hemispheric and Regional Sea Ice Extent and Area Trends from NOAA and NASA Passive Microwave-Derived Climate Records

Walter N Meier,Ann Windnagel,J Scott Stewart,Florence M Fetterer

doi:10.3390/rs14030619

Abstract

Three passive microwave-based sea ice products archived at the National Snow and Ice Data Center (NSIDC) are compared: (1) the NASA Team (NT) algorithm product, (2) Bootstrap (BT) algorithm product, and (3) a new version (Version 4) of the NOAA/NSIDC Climate Data Record (CDR) product. Most notable for the CDR Version 4 is the addition of the early passive microwave record, 1979 to 1987. The focus of this study is on long-term trends in monthly extent and area. In addition to hemispheric trends, regional analysis is also carried out, including use of a new Northern Hemisphere regional mask. The results indicate overall good consistency between the products, with all three products showing strong statistically significant negative trends in the Arctic and small borderline significant positive trends in the Antarctic. Regionally, the patterns are similar, except for a notable outlier of the NT area having a steeper trend in the Central Arctic, likely related to increasing surface melt. Other differences are due to varied approaches to quality control, e.g., weather filtering and correction of mixed land-ocean grid cells. Another factor, particularly in regards to NT trends with BT or CDR, is the inter-sensor calibration approach, which yields small discontinuities between the products. These varied approaches yield small differences in trends. In the Arctic, such differences are not critical, but in the Antarctic, where overall trends are near zero and borderline statistically significant, the differences are potentially important in the interpretation of trends.

Highlights

Multi-channel passive microwave sensors provide a consistent and near-complete long-term time series of sea ice conditions. These data represent one of the longest satellitederived climate records and are a key indicator of climate change over the past 40+ years. They show an Arctic where sea ice is in decline [1,2], while the Antarctic Sea ice environment is more complex with small trends and large interannual variability [2,3]
Sea ice extent is the total area covered by ice above a prescribed concentration threshold, typically 15%
Estimates are in much closer agreement than Climate Data Record (CDR) and NASA Team (NT). This is not surprising given the formulation of the CDR algorithm, which uses the highest concentration from BT and NT at each grid point

Summary

Introduction

Multi-channel passive microwave sensors provide a consistent and near-complete long-term time series of sea ice conditions. These data represent one of the longest satellitederived climate records and are a key indicator of climate change over the past 40+ years. They show an Arctic where sea ice is in decline [1,2], while the Antarctic Sea ice environment is more complex with small trends and large interannual variability [2,3]. The NASA Scanning Multichannel Microwave Radiometer (SMMR) on the Nimbus-7 platform operated from 1978 to 1987. This was followed by a series of Special

Methods

Results

Conclusion