Estimating the uncertainty of sea-ice area and sea-ice extent from satellite retrievals

• Main Authors: Wernecke, Andreas, Notz, Dirk, Kern, Stefan, Lavergne, Thomas
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: article; Verlagsveröffentlichung; Arctic; Global warming; Sea ice
• Online Access: https://doi.org/10.5194/egusphere-2022-1189; https://noa.gwlb.de/receive/cop_mods_00063271; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00068319/egusphere-2022-1189.pdf; https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1189/egusphere-2022-1189.pdf

The net Arctic sea-ice area (SIA) can be estimated from the sea-ice concentration (SIC) by passive microwave measurements from satellites. To be a truly useful metric, for example of the sensitivity of the Arctic sea-ice cover to global warming, we need, however, reliable estimates of its uncertainty. Here we retrieve this uncertainty by taking into account the spatial and temporal error correlations of the underlying local sea ice concentration products. We find that the observational uncertainties of both sea-ice area and sea-ice extent (SIE) in 2015 are about 300 000 km2 for daily and weekly estimates and 160 000 km2 for monthly estimates. This daily uncertainty corresponds to about seven percent of the 2015 sea-ice minimum and is about half of the spread in estimated sea-ice area from different passive microwave SIC products. This shows that random SIC errors play a role in SIA uncertainties comparable to inter-SIC-product biases. We further show that the September SIA, which is traditionally the month with least Arctic sea ice, has declined by 105 000 km2 a-1 ± 9 000 km2 a-1 for the period from 2002 to 2017. This is the first estimate of a SIA trend with an explicit representation of temporal error correlations.