Understanding differences in chemistry climate model projections of stratospheric ozone

Abstract

Chemistry climate models (CCMs) are used to project future evolution of stratospheric ozone as concentrations of ozone-depleting substances (ODSs) decrease and greenhouse gases increase, cooling the stratosphere. CCM projections exhibit not only many common features but also a broad range of values for quantities such as year of ozone return to 1980 and global ozone level at the end of the 21st century. Multiple linear regression is applied to each of 14 CCMs to separate ozone response to ODS concentration change from that due to climate change. We show that the sensitivity of lower stratospheric ozone to chlorine change ΔO 3 /ΔCl y is a near-linear function of partitioning of total inorganic chlorine (Cl y ) into its reservoirs; both Cl y and its partitioning are largely controlled by lower stratospheric transport. CCMs with best performance on transport diagnostics agree with observations for chlorine reservoirs and produce similar ozone responses to chlorine change. After 2035, differences in ΔO 3 /ΔCl y contribute little to the spread in CCM projections as the anthropogenic contribution to Cl y becomes unimportant. Differences among upper stratospheric ozone increases due to temperature decreases are explained by differences in ozone sensitivity to temperature change ΔO 3 /ΔT due to different contributions from various ozone loss processes, each with its own temperature dependence. Ozone decrease in the tropical lower stratosphere caused by a projected speedup in the Brewer-Dobson circulation may or may not be balanced by ozone increases in the middle-and high-latitude lower stratosphere and upper troposphere. This balance, or lack thereof, contributes most to the spread in late 21st century projections.

Impact of Stratospheric Volcanic Aerosols on Age-of-Air and Transport of Long-Lived Species

“…A significant improvement in the new version of the ULAQ-CCM has been reached with respect to the one discussed in Strahan et al [28] and Douglass et al [54]. The model bias relative to SMR observations in the tropical region [55,56] Below 30 hPa, tropical N2O has a very small vertical gradient, because it has essentially no loss from UV photolysis and then volcanic aerosol induced changes in the ascent rate have negligible effect on its mixing ratio.…”

“…A significant improvement in the new version of the ULAQ-CCM has been reached with respect to the one discussed in Strahan et al [28] and Douglass et al [54]. The model bias relative to SMR observations in the tropical region [55,56] Figure 2.…”

Chemical Mechanisms and Their Applications in the Goddard Earth Observing System (GEOS) Earth System Model

“…Successes with GEOS in studying the ozone layer and its relation to climate motivated efforts to enhance its ability to address other topics in chemistry and transport important to NASA's Earth Science Mission (Douglass et al, ; Oman & Douglass, ; Stolarski et al, ). Substantial improvements to the atmospheric physical parameterizations (Molod et al, ) were supplemented by introducing aerosol modules (Colarco et al, ) and by acquiring modern, highly resolved emissions inventories.…”

Influence of the Arctic Oscillation on the Vertical Distribution of Wintertime Ozone in the Stratosphere and Upper Troposphere over the Northern Hemisphere

“…However, interpretation of long-term ozone variation is difficult since the ozone field exhibits not only a complicated trend, forced by changes in ozone-depleting substances superimposed on a changing climate, but also interannual variability related to various meteorological conditions (e.g., Weiss et al 2001;Hadjinicolaou et al 2002;Tian and Chipperfield 2005;Austin et al 2010;Eyring et al 2010;Liu et al 2013;Douglass et al 2014). The World Meteorological Organization (WMO 2007(WMO , 2011 highlighted the fact that meteorology can also significantly influence the long-term trend of total ozone column (TOC); in particular, meteorological variability can explain as much as 20%-50% of TOC variability in the extratropics of the Northern Hemisphere during winter and spring.…”