Arctic stratospheric ozone depletion is closely linked to the
occurrence of low stratospheric temperatures. There are indications
that cold winters in the Arctic stratosphere have been getting colder,
raising the question if and to what extent a cooling of the Arctic
stratosphere may continue into the future. We use meteorological
reanalyses from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim and NASA's Modern-Era Retrospective-Analysis for Research and Applications (MERRA) for the past 32 yr together with
calculations of the chemistry-climate model (CCM) ECHAM/MESSy Atmospheric Chemistry (EMAC) and models from
the Chemistry-Climate Model Validation (CCMVal) project to infer radiative and dynamical contributions to
long-term Arctic stratospheric temperature changes. For the past
three decades the reanalyses show a warming trend in winter and cooling
trend in spring and summer, which agree well with trends from the Radiosonde Innovation Composite Homogenization (RICH) adjusted radiosonde data set. Changes in winter and spring are caused
by a corresponding change of planetary wave activity with increases in
winter and decreases in spring. During winter the increase of
planetary wave activity is counteracted by a residual radiatively induced
cooling. Stratospheric radiatively induced cooling is detected
throughout all seasons, being highly significant in spring and
summer. This means that for a given dynamical situation, according to
ERA-Interim the annual mean temperature of the Arctic lower
stratosphere has been cooling by
−0.41 ± 0.11 K decade−1 at 50 hPa over the
past 32 yr. Calculations with state-of-the-art models from
CCMVal and the EMAC model qualitatively reproduce the radiatively induced cooling for
the past decades, but underestimate the amount of radiatively induced
cooling deduced from reanalyses.
There are indications that this discrepancy could be partly related to
a possible underestimation of past Arctic ozone trends in the models.
The models project a continued cooling of the Arctic stratosphere over
the coming decades (2001–2049) that
is for the annual mean about 40% less than the modeled cooling for the past, due
to the reduction of ozone depleting substances and the resulting ozone
recovery. This projected cooling in turn could offset between 15 and 40%
of the Arctic ozone recovery
