In the last decades, a number of changes have been observed including the inflow of warmer Atlantic water masses into the Arctic Ocean, changes in atmospheric oscillation patterns and reduction of Arctic sea ice (more in ACIA report, 2005).
Reasons for the Arctic amplification are still under debate
The reasons for the Arctic amplification are still a subject of debate. Beside the so-called ice-albedo feedback, several other processes such as increased atmospheric advection of heat and moisture from mid-latitudes and enhanced import of saline and warm north-Atlantic water and the slightly fresher and somewhat cooler Pacific water potentially play a role. Also changing clouds and cloud properties have been implicated as reasons for the amplification. To what degree natural variability and anthropogenic climate change contribute to these changes remains to be determined.
Mechanisms analysed with EC-Earth
Mechanisms behind the Arctic amplification will be analysed in transient EC-Earth simulations covering both the recent past as well as future scenarios. The relative roles of external influences and internal processes will be explored in relation to their role in the Arctic in numerical experiments. Such experiments are complements to recent work investigating the Arctic amplification based on reanalyses (Graversen et al. 2008), which suffer from artificial sources and sinks of energy and mass, discontinuity of observational inputs and lack of dynamic sea ice models. EC-Earth provides several advantages and developments in work, such as a new and improved sea ice model (LIM3) and an advanced double-moment cloud microphysical scheme, which we believe will enable us to investigate the main mechanisms behind the Arctic amplification in a self-consistent manner.
ACIA, 2005. Arctic Climate Impact Assessment. Cambridge University Press, New York.
Graversen, R.G., T. Mauritsen, MT, E. Källen and G. Svensson, 2008: Vertical structure of recent Arctic warming, Nature, 541, doi:10.1038.