Relative contributions of different mechanisms to changes in ozone in the 21st century

Stratospheric ozone is expected to increase this century as the abundance of stratospheric halogens decreased to pre-1980 values. However, as a result of climate change, there may be changes in stratospheric temperature, circulation and composition that could alter this "recovery" of stratospheric ozone. Here we quantify the contribution of different mechanisms (changes in stratospheric composition, temperature and circulation) to changes in ozone from the NASA GSFC chemistry-climate model, using multiple linear regression analysis and chemical box model calculations.

It is shown that above 30 km the extra-polar ozone has a secular increase over the next 100 years. This increase is determined by the decrease in halogen amounts and the greenhouse gas induced cooling. These two effects result in ozone levels that are greater 2090s than in the 1960s. Changes in NOy have a significant role in year-to-year variability, but only a minor role in long-term changes. Below 30 km changes in transport play an increasing role. In tropical latitudes ozone decreases through the 21st century, even as halogens return to 1960s levels. This decrease is caused by an increase in the tropical upwelling. In polar regions the long term changes in ozone are dominated by changes in halogens, with temperature and transport causing large year-to-year variations.