September Arctic sea ice minimum predicted by spring melt pond fraction

Abstract:

The area of Arctic September sea ice has diminished from about 7 million km2 in the 1990s to less than 5 million km2 in 5 of the last 7 years with a record minimum of 3.6 million km2 in 2012. The strength of this decrease is greater than expected by the scientific community, the reasons for this are not fully understood, and its simulation is an on-going challenge for existing climate models. With growing Arctic marine activity there is an urgent demand for forecasting Arctic summer sea ice. Previous attempts at seasonal forecasts of ice extent were of limited skill. However, here we show that the Arctic sea ice minimum can be accurately forecasted from melt pond area in spring. We developed a physical based melt pond model suitable for forecasting the evolution of melt ponds and incorporated this model into the Los Alamos sea ice model CICE. We find a strong correlation between the simulated spring pond fraction and the observed September sea ice extent for the period 1979 to 2013. This is explained by a positive feedback mechanism: more ponds reduce the albedo; a lower albedo causes more melting; more melting increases pond fraction. Our results help explain the acceleration of Arctic sea ice decrease during the last decade. We are able to predict the observed September ice area with a similar degree of skill as the observed ice extent. The choice of the applied SSM/I algorithm (NASA Team or bootstrap) does not materially affect our results. The inclusion of our new melt pond model promises to improve the skill of future forecast and climate models in Arctic regions and beyond.