Contributed by: Torben Koenigk, Peter Berg, Ralf Döscher, SMHI

The Arctic is an important region for the entire world’s climate system. Sea ice and snow dominate the heat and mass exchanges between atmosphere and ocean and freshwater exports from the Arctic Ocean can potentially affect the entire world’s ocean circulation. Observations of recent decades show a dramatic reduction of Arctic sea ice and this has been linked to changes in the atmospheric circulations and extreme events in northern mid-latitudes.

Global climate models still have deficiencies in simulating the observed Arctic sea ice extent and trend and are still too coarse to adequately simulate small-scale processes near the ice edge or in complex terrain. The WCRP “Coordinated Downscaling Experiment” (CORDEX) organizes dynamical downscaling with regional climate models of global model data from the “Coupled Model Intercomparison Project Phase 5” (CMIP5) in order to provide more reliable information for future climate change on the local scale. As part of the “Polar-CORDEX” downscaling effort, this study used an Arctic regional atmosphere model to downscale historical simulations and future climate scenarios from four global climate models and compared the regional model results to the original results from the global models. 

1-Koenigk-ArcticCORDEXFor the period from 1980-2005, regional and global simulations show similar deviations of large-scale wind and temperature fields from observations in the Arctic. However, locally, important differences occur. For example, we see a reduced winter air temperature bias over the Arctic Ocean but increased spring and summer biases over land areas in our regional model.

The projected future changes indicate a strong warming in the Arctic, exceeding 15 °C in autumn and winter over the Arctic Ocean under the high emission scenario RCP8.5 until the end of the 21st century. The winter-time temperature inversion strength is reduced, leading to a less stable stratification of the Arctic atmosphere and increased precipitation. Most of the large-scale change patterns are similar in the regional models and the driving global models, however some differences occur. The most important differences are stronger summer precipitation increase and reduced future warming over the Arctic Ocean in the regional model.

The regional simulations were performed at a 50 km resolution; this seems still be too coarse to resolve many important processes and thus the improvements of large-scale processes in these regional simulations are limited. Future work should thus explore if regional simulations with much higher resolution show enhanced added value compared to the global model simulations. A special focus should be on process studies, extreme events and on areas with complex orography.

For more information, read the full paper: http://www.polarresearch.net/index.php/polar/article/view/24603

Citation: Koenigk, Torben, Peter Berg, & Ralf Döscher. “Arctic climate change in an ensemble of regional CORDEX simulations.” Polar Research 2015, 34, 24603, http://dx.doi.org/10.3402/polar.v34.24603