| Summary: | Both Arctic and Antarctic sea ice are being affected by climate change. While Arctic sea ice has been declining for several decades, the behavior of Antarctic sea ice was stable before an abrupt increase in its extent from 2012 to 2015, followed by a steep fall in 2016. Sea ice changes need to be quantified to estimate feedback on ocean, atmosphere and ecosystems as well as for arctic communities that are evolving in the most impacted region. Quantifying volumes changes at both basin scales rely on sea ice concentration and thickness observations. While long-term changes in sea ice area are well described, long-term sea ice thickness estimations remain too sparse in space and time to capture the global evolution of sea ice volume. Here 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, and the regional sea ice thickness changes heterogeneity for the Antarctic. The study enhances that most of the variability in volume is attributed to variability in thickness, holding for the two hemispheres. This first sea ice thickness time series offers a new insight for models, and the possibility to improve sea ice forecasting, especially in Antarctica where models thickness appear to be low biased.
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