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© Author(s) 2009. Chiara Cagnazzo is supported by the Centro Euro-Mediterraneo per i Cambiamenti Climatici. Elisa Manzini acknowledges the support of the EC SCOUT-O3 Integrated Project (505390-GOCE-CT-2004) for part of this work. Natalia Calvo was supported by the Spanish Ministry of Education and Science and the Fulbright Commission in Spain. CCSRNIES’s research has been supported by the Global Environmental Research Fund (GERF) of the Ministry of the Environment (MOE) of Japan (A-071). MRI simulations have been made partly with the MRI supercomputer and partly with the NIES supercomputer. CMAM simulations were supported by the Canadian Foundation for Climate and Atmospheric Sciences and run on the Environment Canada Supercomputer. We acknowledge the modeling groups for making their simulations available for this analysis, the Chemistry-Climate Model Validation Activity (CCMVal) for WCRP’s (World Climate Research Programme) SPARC (Stratospheric Processes and their Role in Climate) project for organizing and coordinating the model data analysis activity, and the British Atmospheric Data Center (BADC) for collecting and archiving the CCMVal model output. Chiara Cagnazzo and Elisa Manzini are grateful to Antonio Navarra for useful discussions. We are thankful to John Austin for suggestions and discussions on the manuscript., The connection between the El Nino Southern Oscillation (ENSO) and the Northern polar stratosphere has been established from observations and atmospheric modeling. Here a systematic inter-comparison of the sensitivity of the modeled stratosphere to ENSO in Chemistry Climate Models (CCMs) is reported. This work uses results from a number of the CCMs included in the 2006 ozone assessment. In the lower stratosphere, the mean of all model simulations reports a warming of the polar vortex during strong ENSO events in February-March, consistent with but smaller than the estimate from satellite observations and ERA40 reanalysis. The anomalous warming is associated with an anomalous dynamical increase of column ozone north of 70 degrees N that is accompanied by coherent column ozone decrease in the Tropics, in agreement with that deduced from the NIWA column ozone database, implying an increased residual circulation in the mean of all model simulations during ENSO. The spread in the model responses is partly due to the large internal stratospheric variability and it is shown that it crucially depends on the representation of the tropospheric ENSO teleconnection in the models., Canadian Foundation for Climate and Atmospheric Sciences, EC SCOUT-O3 Integrated Project, Spanish Ministry of Education and Science, Ministry of the Environment (MOE) of Japan, Fulbright Commission in Spain, Euro-Mediterraneo per i Cambiamenti Climatici, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

A tighter integration of modeling frameworks for climate and air quality is urgently needed to assess the impacts of clean air policies on future Arctic and global climate. We combined a new model emulator and comprehensive emissions scenarios for air pollutants and greenhouse gases to assess climate and human health co-benefits of emissions reductions. Fossil fuel use is projected to rapidly decline in an increasingly sustainable world, resulting in far-reaching air quality benefits. Despite human health benefits, reductions in sulfur emissions in a more sustainable world could enhance Arctic warming by 0.8 °C in 2050 relative to the 1995–2014, thereby offsetting climate benefits of greenhouse gas reductions. Targeted and technically feasible emissions reduction opportunities exist for achieving simultaneous climate and human health co-benefits. It would be particularly beneficial to unlock a newly identified mitigation potential for carbon particulate matter, yielding Arctic climate benefits equivalent to those from carbon dioxide reductions by 2050.