Parameterized stratospheric ozone photochemistry has been included in
the Goddard Institute for Space Studies (GISS) GCM to investigate the
coupling between chemistry and climate change for the doubled CO2 clim
ate. The chemical ozone response is of opposite sign to temperature ch
anges, so that radiative cooling in the upper stratosphere results in
increased ozone, while warming reduces ozone in the lower stratosphere
. The increased overhead column reduces the amount of UV reaching the
lower stratosphere, resulting in further ozone decreases there. Change
s of up to 15% are seen, including both photochemistry and transport.
Good agreement is found between the authors' results and those in othe
r models for tropical latitudes where the stratospheric temperature re
sponses are similar. However, in the extratropics, there are large dif
ferences between present results and those of the other models due to
differences in tropospheric warming and tropospheric forcing of the st
ratospheric residual circulation. A net decrease in column ozone at mi
dlatitudes is seen in this climate model, in contrast to the other mod
els that showed an increase in column ozone everywhere. These ozone re
ductions lead to an increase of 10% in UV radiation reaching the surfa
ce at northern midlatitudes. The authors find significantly less of an
increase in the high-latitude ozone column than in the other models.
When parameterized heterogeneous chemistry on polar stratospheric clou
ds is also included, while maintaining current chlorine loading, it is
found that the Antarctic ozone hole becomes significantly larger and
of longer duration. In addition, an ozone hole of approximately half t
he depth in percent of the current Antarctic ozone hole forms in the A
rctic due to both chemistry and transport changes resulting from a red
uction of sudden warmings seen in the doubled CO2 atmosphere.