final_program_abstracts[1]

11 IMSC Session Program
Ocean heat transport as a key process for model spread in
Arctic warming
Friday - Parallel Session 6
Irina Mahlstein and Reto Knutti
Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
The Arctic region is characterized by a very large variability and complex physical
processes which govern its climate. Global warming caused by anthropogenic
greenhouse gases impacts this region severely by changes in sea ice cover which have
strong implications for the heat budget. Numerous physical processes account for the
strength of the ice albedo feedback which is mainly responsible for polar
amplification. Simulating future temperature increase in this region is challenging due
to the complexity of this particular climate system. Atmosphere Ocean Global
Circulation Models (AOGCM) show large uncertainties in their projections for this
region. The range of simulated future temperatures until 2100 across the different
AOGCMs covers 2.5-7.5K compared to 0.5-4K for the global temperature increase.
However, models showing a large warming in the Arctic project a larger global
warming, as well. Understanding the Arctic climate system with all its feedbacks is
therefore indispensable in order to reduce uncertainty in global climate projections.
In this study we show that the main differences in the pattern of the simulated surface
temperatures of the AOGCMs are localized over the Barents Sea. This is a region
where surface temperature depends on ocean currents, namely the North Atlantic Drift
Stream bringing warm surface water to high latitudes. The strength of the northward
ocean heat transport on the other hand impacts the sea ice cover in this region. Less
sea ice leads to a stronger warming. Comparisons with observations reveal that those
models which have a stronger northward ocean heat transport simulate the sea ice
extent more accurately than those which have a weaker ocean heat transport.
Transporting less energy to the north induces more sea ice in the Arctic and
consequently the future polar warming is less pronounced in these projections.
Constraining climate simulations of the northward ocean heat transport with
observations offers one possibility to reduce uncertainty in future projections.
However, obtaining accurate observations of the ocean heat transport is very
challenging.
Abstracts 356