Thursday, 11 June 2009: 11:40 AM
Stratospheric ozone is expected to increase during the 21st century as the abundance of halogenated ozone-depleting substances decreases to 1960 values. However, climate change will likely alter this recovery of stratospheric ozone by changing stratospheric temperatures, circulation and abundance of reactive chemical species. Here we quantify the contribution of different mechanisms to changes in ozone from 1960 to 2100 in the Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM), using multiple linear regression analysis applied to simulations using either A1b or A2 greenhouse gas (GHG) scenarios. Upper stratospheric extra-polar ozone has a secular increase over the 21st century. For the simulation using the A1b GHG scenario, this increase is determined by the decrease in halogen amounts and the greenhouse gas-induced cooling, with roughly equal contributions from each mechanism. There is a larger cooling in the simulation using the A2 GHG scenario, but also enhanced loss from higher NOy and HOx concentrations, which largely offsets the increase due to cooler temperatures. The resulting ozone trends are similar in the A2 and A1b simulations. Also, using simulations with fixed low halogen concentrations we quantify feedbacks related to temperature and HOx changes in response to changing halogen concentrations.
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