ALBERT

Description: 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 re-analyses from ERA-Interim for the past 32 yr together with calculations of the chemistry-climate model EMAC and CCM models from the CCMVal project to infer radiative and dynamical contributions to long-term Arctic stratospheric temperature changes. For the past three decades ERA-Interim shows a warming trend in winter and cooling trend in spring and summer. 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 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, in 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 confirm the radiatively induced cooling for the past decades, but underestimate the amount of radiatively induced cooling deduced from ERA-Interim. EMAC predicts a continued annual radiatively induced cooling for the coming decades (2001–2049) of −0.15 ± 0.06 K decade−1 where the projected increase of CO2 accounts for about 2/3 of the cooling effect. Expected decrease of stratospheric halogen loading and resulting ozone recovery in the future counteracts the cooling tendency due to increasing greenhouse gas concentrations and leads to a reduced future cooling trend compared to the past. CCMVal multi-model mean predicts a future annual mean radiatively induced cooling of −0.10 ± 0.02 K decade−1 which is also smaller in the future than in the past.