Arctic Snow Depth, Ice Thickness, and Volume From ICESat-2 and CryoSat-2: 2018–2021 — Watts Up With That?

New paper and of course it’s worse than we thought.

New estimates of snow depth, from a combination of lidar and radar, improve sea-ice thickness estimates, according to a new study in AGU’s Geophysical Research Letters. Arctic sea ice has lost 16% of its thickness in the last three years, the study finds.
Credit: NASA/Kathryn Hansen

According to the press release:

– End-of-season Arctic multiyear sea ice is about 1.5 feet thinner in 2021 than in 2019

– Arctic Ocean sea ice lost one-third of its volume in the past 18 years

– New pan-Arctic snow depth suggests previous estimates of sea ice thickness may have been overestimated


WASHINGTON—Over the past two decades, the Arctic has lost about one-third of its winter sea ice volume, largely due to a decline in sea ice that persists over several years, called multiyear ice, according to a new study. The study also found sea ice is likely thinner than previous estimates.

Seasonal sea ice, which melts completely each summer rather than accumulating over years, is replacing thicker, multiyear ice and driving sea ice thinning trends, according to the new research.

And straight out of Rick’s Cabaret, I’m shocked I tell you.

“We weren’t really expecting to see this decline, for the ice to be this much thinner in just three short years,” said lead study author Sahra Kacimi, a polar scientist at the California Institute of Technology’s Jet Propulsion Laboratory.

Here’s the paper.

First published: 10 March 2022 |


Using ICESat-2 and CryoSat-2 freeboards, we examine the variability of monthly Arctic sea ice snow depth, thickness and volume between October 2018 and April 2021. For the 3 years, satellite-derived estimates captured a decrease in mean April snow depth (∼2.50 cm) and ice thickness (∼0.28 m) equivalent to an ice volume loss of ∼12.5%. Results show greater thinning of multiyear ice with an end-of-season thickness in 2021 that is lower by ∼16.1% (0.50 m), with negligible changes over first-year ice. For the period, sea ice thickness estimates using snow depth from climatology result in thicker ice (by up to ∼0.22 m) with a smaller decrease in multiyear ice thickness (∼0.38 m). An 18-year satellite record, since the launch of ICESat, points to a loss of ∼6,000 km3 or one-third of the winter Arctic ice volume driven by decline in multiyear-ice coverage in the multi-decadal transition to a largely seasonal ice cover.

Plain Language Summary

Ice thickness and volume are critical variables for assessing the evolution and response of the polar sea ice cover to a warming climate. Retrieval of sea ice thickness from altimeter freeboards (i.e., the vertical height of the floating ice and snow above the local sea level) requires knowledge of loading due to snow. Until recently, snow depth has been prescribed with a climatology based on historical field records. Using freeboard differences from ICESat-2 and CryoSat-2, we are now able to derive snow depth estimates. In this paper we examine the differences between climatological and satellite-derived snow depth as well as the retrieved ice thicknesses from the two altimeter missions. Their changes for three winters between 2018 and 2021 are documented. Derived ice volume estimates are placed within the context of an 18-year satellite record.

1 Introduction

As of December 2021, ICESat-2 has completed its 3-year prime mission (Markus et al., 2017) and is currently in extended operation. For the ice-covered Arctic Ocean, the lidar on the ICESat-2 observatory is tasked to provide the heights of sea ice and local sea surfaces for the calculation of freeboard—the vertical height of the floating ice above the local sea level. The retrieved total freeboard (snow plus ice) facilitates the estimation of thickness of the Arctic and Southern Ocean ice covers. The non-stop operations (with only a few interruptions) have provided all season coverage of the polar oceans. Here, we examine estimates of Arctic snow depth and ice thickness between October 2018 and April 2021.

Time-varying snow depth over sea ice, for computing snow loading, has been a limiting factor in the accuracy of sea ice thickness estimates. Prior to the launch of ICESat-2, the potential of combining ICESat-2 (IS-2) and CryoSat-2 (CS-2) freeboards to provide estimates of snow depth was recognized by Kwok and Markus (2017). The measurement concept is based on differencing the freeboards from IS-2 (which measures the height of the air-snow interface above the local sea surface) and CS-2 (which measures the height of the snow-ice interface above the local sea surface). For one Arctic growth season (October 2018 to April 2019), Kwok et al. (2020) provided a first examination of the snow depth retrievals using IS-2 and CS-2 freeboards. Results showed that the snow depths compared well with airborne estimates and spatial patterns of reconstructed snowfields. As well, the variability of the freeboards, derived snow depth, and ice thickness estimates was assessed in the Antarctic (Kacimi & Kwok, 2020).

In this paper, we examine the interannual variability of the freeboard-derived snow depth, ice thickness and volume over the first three winters of IS-2 operations (between October 2018 and April 2021). The paper is organized as follows. The next section describes the data used in this analysis. Section 3 briefly describes the two different estimates of snow depths used here – one from the IS-2 and CS-2 freeboards and the other from a modified Warren climatology (Kwok & Cunningham, 2015; Warren et al., 1999) – followed by an analysis of their spatial variability and seasonal evolution. In Section 4, we describe the calculated sea ice thickness and volume from IS-2 and CS-2, and the observed interannual variability. Section 5 summarizes the record of ice volume estimates since the launch of ICESat in 2003. The last section concludes the paper.

Read the full paper here.

via Watts Up With That?

March 12, 2022