Stratospheric ozone loss and climate change

Since it was first realized that low temperatures (and high chlorine amounts) drove the polar ozone loss, there has been speculation regarding possible connections between the build-up of CO₂ and other IR-active gases and polar ozone loss. The increase of these greenhouse gases, while leading to increased IR heating in the troposphere leads to enhanced cooling in the stratosphere and stratosphere temperatures are expected to decrease due to cooling to space from the increased levels of CO₂. In fact, this change in the vertical temperature profile has been detected and is taken as strong evidence for a human influence on climate [17]. This increased stratospheric cooling could affect stratospheric dynamics by making the boreal vortex more robust [18] and could lead to an Arctic ozone hole if CFCs continued to increase. The recent work by Shindell et al. [19] using a GCM with chemistry suggests that the stratospheric cooling will lead to a prolongation of ozone loss due to cooler temperatures and PSC formation even though chlorine levels decrease.

As noted above, Shindell et al. [19] used a Global Climate/Middle Atmospheric Model (GCMAM) with simplified chemistry and constrained ozone transport to investigate the coupling between chemistry and climate. For the period 2010-2019 they found that the increase due to radiative cooling of the stratosphere was 1-2 K poleward of 70°N while there was an additional cooling of 8-10 K attributable to the increased stability of the Arctic vortex. This dramatic decline in stratospheric temperatures in their model caused an Arctic ozone hole in the spring with a 2/3 loss of the total ozone column. An Arctic ozone hole is thus predicted to occur in years 2010-2019, in spite of anticipated decreases of CFC concentrations because of the implementation of the Montreal protocol.

The possibility of an Arctic ozone hole is a very disturbing development with strong political and social implications. In contrast to the Antarctic ozone hole, an Arctic ozone hole would affect heavily populated parts of the Northern Hemisphere. Our experimental and theoretical understanding of Arctic chemistry is still in a primitive state. The possibility of the development of an Arctic ozone hole clearly will require more detailed modelling studies combined with a detailed complement of measurements. ACE can contribute to our understanding of the physics, chemistry and dynamics of the Arctic polar stratosphere.

References

17. Santer, B.D. et al., (1996) A search for human influences on the thermal structure of the atmosphere, Nature, 382, 39-46.
18. Austin, J., et al., (1992) Possibility of an Arctic ozone hole in a doubled-CO₂ climate, Nature, 360, 221-225.
19. Shindell, D.T., Rind, D. and Lonergan, P., (1998) Increased polar stratospheric ozone losses and delayed eventual recovery owing to increased greenhouse-gas concentrations, Nature, 392, 589.