Seasonal and regional sensitivity of Arctic sea ice

We examine the seasonal and regional evolution of sea-ice coverage in the Arctic in response to changes in the forcing. Using satellite and reanalysis data in combination with CMIP6 model simulations, we build on previous studies that have found a strong linear relationship between the September sea-ice area of the northern hemisphere and global atmospheric air temperature (TAS) as well as anthropogenic CO₂ emissions. Instead of focusing on the whole Arctic and September sea ice only, we perform sensitivity analyses on higher-resolved regional and seasonal scales, aiming to identify the atmospheric and oceanic drivers that govern the evolution of sea-ice coverage on these scales and to derive simple empirical relationships that describe the impact of these processes. We find clear linkages also on these higher-resolved scales, with different regions and different seasons showing diverse sensitivities of sea-ice area evolution with respect to TAS and anthropogenic CO₂. Furthermore, we use a multivariate metric to quantify the "quality" of a single simulation matching the observations, thereby considering the different sensitivities of all seasons of the year. Building the combined covariance matrix of observations and simulations as a measure of the joint uncertainties, we can determine how "close" to the observations every single member of the simulations is. This allows us to separate models whose sensitivities are in overall good agreement with the observations from those that are apparently not capable of properly simulating the response of the sea ice to the forcing throughout all months. Based on our findings we can infer the dominant drivers that force Arctic sea-ice evolution on a regional and seasonal scale and also derive projections for the future evolution of Arctic sea ice for different climate scenarios based on simple empirical relationships that can directly be estimated from observational records.