Arctic and Antarctic Sea Ice Thickness and Volume Changes From Observations Between 1994 and 2023.

Both Arctic and Antarctic sea ice are affected by climate change. While Arctic sea ice has been declining for several decades, Antarctic sea ice extent slowly increased until 2015, followed by a sharp drop in 2016. Quantifying sea ice changes is essential to assess their impacts on the ocean, atmosphere, ecosystems and Arctic communities. In this study, we combine sea ice thickness estimates from four satellite radar altimeters to derive the longest time series of homogeneous sea ice thickness for both hemispheres over 30 years (1994–2023). The record supports the rapid loss of sea ice in the Arctic for each month of the year and the heterogeneous changes in sea ice thickness in the Antarctic. The study confirms that most of the volume variability is due to the thickness variability, which holds true for both hemispheres. The sea ice thickness time series presented here offer new insights for models, in particular the possibility to evaluate sea ice reanalyses and to initialize forecasts, especially in the Antarctic, where the data set presented here has no equivalent in terms of spatial and temporal coverage. Plain Language Summary: Arctic and Antarctic sea ice respond significantly to climate change, as documented by decades of satellite records of sea ice coverage. Arctic sea ice coverage has declined steadily over the past 40 years, while Antarctic sea ice coverage increased until 2016, followed by a rapid decline. In contrast, changes in sea ice thickness, which contribute to changes in sea ice volume, are much less well documented due to the lack of long‐term observations. In this study, we address this gap by producing a 30‐year time series of sea ice thickness (1994–2023) using data from four satellite radar altimeters, representing the longest consistent data set for both polar regions. This was made possible by using machine learning to align the different satellite missions and incorporating an ensemble of snow depth products to cover the entire period. The resulting time series shows a rapid decrease in Arctic sea ice thickness over the study period. In contrast, Antarctic sea ice shows thickness changes with significant spatial variability. This new data set provides critical insights into sea ice dynamics, their causes, and their impacts on climate, ecosystems, and Arctic communities. Key Points: A 30‐year data set from four satellite radar altimeters provides the longest sea ice thickness record for both polar regionsArctic sea ice is significantly thinning for each month of the year, whereas Antarctic undergoes complex regional thickness changesSea ice volume variability can be explained by sea ice thickness variability in both polar hemispheres [ABSTRACT FROM AUTHOR]