Investigating future changes in the volume budget of the Arctic sea ice in a coupled climate model
2017
Abstract. We present a method for analysing changes in the modelled volume budget of
the Arctic sea ice as the ice declines during the 21st century. We apply the
method to the CMIP5 global coupled model HadGEM2-ES to evaluate how the
budget components evolve under a range of different forcing scenarios. As the
climate warms and the ice cover declines, the sea ice processes that change
the most in HadGEM2-ES are summer melting at the top surface of the ice due
to increased net downward radiation and basal melting due to extra heat from
the warming ocean. There is also extra basal ice formation due to the
thinning ice. However, the impact of these changes on the volume budget is
affected by the declining ice cover. For example, as the autumn ice cover
declines the volume of ice formed by basal growth declines as there is a
reduced area over which this ice growth can occur. As a result, the biggest
contribution to Arctic ice decline in HadGEM2-ES is the reduction in the
total amount of basal ice growth during the autumn and early winter. Changes in the volume budget during the 21st century have a distinctive
seasonal cycle, with processes contributing to ice decline occurring in
May–June and September to November. During July and August the total amount
of sea ice melt decreases, again due to the reducing ice cover. The choice of forcing scenario affects the rate of ice decline and the timing
and magnitude of changes in the volume budget components. For the HadGEM2-ES
model and for the range of scenarios considered for CMIP5, the mean changes
in the volume budget depend strongly on the evolving ice area and are
independent of the speed at which the ice cover declines.
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