"Recent Northern Hemisphere tropical expansion primarily driven by black carbon and tropospheric ozone", new study suggests

Observational analyses have shown the width of the tropical belt increasing in recent decades as the world has warmed. This expansion is important because it is associated with shifts in large-scale atmospheric circulationand major climate zones. Inn a new study, just published in "Nature" journal,  a climate model with detailed aerosol physics is used to show that increases in heterogeneous warming agents—including black carbon aerosols and tropospheric ozone—are noticeably better than greenhouse gases at driving expansion, and can account for the observed summertime maximum in tropical expansion. Mechanistically, atmospheric heating from black carbon and tropospheric ozone has occurred at the mid-latitudes, generating a poleward shift of the tropospheric jet, thereby relocating the main division between tropical and temperature air masses. More in http://www.nature.com/nature/journal/v485/n7398/full/nature11097.html?WT.ec_id=NATURE-20120517