| The Arctic amplification of global warming, and the pronounced Arctic sea-ice
retreat constitute some of the most alarming signs of global climate change. These
Arctic changes are likely a consequence of a combination of several processes, for
instance enhanced uptake of solar radiation in the Arctic due to a decrease of sea ice
(the ice-albedo feedback), and increase in the local Arctic greenhouse effect due
to enhanced moister flux from lower latitudes. Many of the proposed processes
appear to be dependent on each other, for instance an increase in water-vapour
advection to the Arctic enhances the greenhouse effect in the Arctic and the longwave
radiation to the surface, leading to sea-ice melt and enhancement of the ice-albedo
feedback.
The effects of albedo changes and other radiative feedbacks have been investigated in
earlier studies based on model experiments designed to examine these effects specifically.
Here we instead focus on the effects of meridional transport changes into the Arctic, both of
moister and dry-static energy. Hence we here present results of model experiments with the
CESM climate model designed specifically to extract the effects of the changes of the two
transport components.
In the CESM model the moister transport to the Arctic increases, whereas the dry-static
transport decreases in response to a doubling of CO2. This is in agreement with other model
results. The model is now forced with these transport changes of water-vapour and
dry-static energy associated with a CO2 doubling. The results show that changes of the
water-vapour transport lead to Arctic warming. This is partly a consequence of the
ice-albedo feedback due to sea-ice melt caused by the change of the water-vapour
advection. The changes of the dry-static transport lead to Arctic cooling, which
however is smaller than the warming induced by the water-vapour component.
Hence this study support the hypothesis that changes in the atmospheric circulation
contribute to the Arctic temperature amplification of the ongoing global warming. |