Relative contribution of feedback processes to Arctic amplification of temperature change in MIROC GCM
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The finding that surface warming over the Arctic exceeds that over the rest of the world under global warming is a robust feature among general circulation models (GCMs). While various mechanisms have been proposed, quantifying their relative contributions is an important task in order to understand model behavior. Here we apply a recently proposed feedback analysis technique to an atmosphere–ocean GCM under two and four times CO2 concentrations which approximately lead to seasonally and annually sea ice-free climates. The contribution of feedbacks to Arctic temperature change is investigated. The surface warming in the Arctic is contributed by albedo, water vapour and large-scale condensation feedbacks and reduced by the evaporative cooling feedback. The surface warming contrast between the Arctic and the global averages (AA) is maintained by albedo and evaporative cooling feedbacks. The latter contributes to AA predominantly by cooling the low latitudes more than the Arctic. Latent heat transport into the Arctic increases and hence evaporative cooling plus large-scale condensation feedback contributes positively to AA. On the other hand, dry-static energy transport into the Arctic decreases and hence dynamical heating feedback contributes negatively to AA. An important contribution is thus made via changes in hydrological cycle and not via the ‘dry’ heat transport process. A larger response near the surface than aloft in the Arctic is maintained by the albedo, water vapour, and dynamical heating feedbacks, in which the albedo and water vapour feedbacks contribute through warming the surface more than aloft, and the dynamical heating feedback contributes by cooling aloft more than the surface. In our experiments, ocean and sea ice dynamics play a secondary role. It is shown that a different level of CO2 increase introduces a latitudinal and seasonal difference into the feedbacks.
KeywordsAtlantic Meridional Overturn Circulation Albedo Feedback Water Vapour Feedback Arctic Warming Poleward Heat Transport
The AOGCM and ASGCM experiments were carried out on the JAMSTEC Earth Simulator and the NIES supercomputer system (NEC SX-8R/128M16), respectively. We thank developers of freely available software, NCL. Constructive comments by Jianhua Lu and two anonymous reviewers are greatly appreciated. This research was supported by the Environment Research and Technology Development Fund (S-10) of the Japanese Ministry of the Environment and GRENE Arctic Climate Change Research Project. The contribution to this work from NIES was supported by the Program for Risk Information on Climate Change (PRICC).
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