Reconstructing seasonal Antarctic sea ice extent during the 20th century

Measurements of Antarctic sea ice extent, defined as the equatorward most region where sea ice concentration drops below 15%, are made using satellite remote sensing. These measurements show unique changes in Antarctica: a slow and steady increase from 1979 when observations began until 2016, followed by a dramatic sudden decline to record low values during 2016-2019. In 2020, partly tied to an emerging La Niña event, the Antarctic sea ice extent rebounded to near and above-average in late 2020. Yet, these causes of these changes, their connection to global climate change, and how unique they are in a historical perspective remain challenging to fully understand, since the observational record is just over 40 years long. This makes Antarctic sea ice one of the shortest continuous measurements of any climate parameter on Earth, yet one that is showing rapid variability and change with potential global consequences through connections with the Southern Ocean and grounded Antarctic Ice Sheet.

In an effort to provide a more reliable historical estimate of Antarctic sea ice extent, a collaborative project funded by the National Science Foundation between Ohio University and UCLA is working to reconstruct Antarctic sea ice extent throughout the 20^th century using a suite of statistical approaches. This talk will present some of the preliminary reconstructions from the Ohio University portion of this effort, which alone clearly demonstrate that robust and skillful reconstructions of Antarctic sea ice extent are possible. These reconstructions then have the potential to provide a wealth of new information to help place current Antarctic climate variability and change in a much needed longer historical perspective.