CliMAS Colloquia

Spice in the Air

 The molar mass of water vapor is lower than that of dry air, making humid air lighter at the same temperature and pressure. This vapor buoyancy effect has often been considered negligible and overlooked in large-scale climate dynamics. However, our study shows that vapor buoyancy significantly impacts atmospheric circulations, planetary energy balance, cloud cover, and land surface temperatures. For instance, vapor buoyancy causes rising air to be, on average, colder than sinking air in the tropical free troposphere. Notably, some state-of-the-art climate models fail to represent vapor buoyancy properly. This flaw leads to inaccurate simulations of cloud distributions—the largest uncertainty in predicting climate change.