Hello, and welcome back! In the previous post, we discussed how big poofy hairstyles were partially to blame for the ozone depletion (spoiler: hairspray aerosols contained CFCs!). We learnt how CFCs and HCFCs contributed to the depletion of the ozone layer and how we have slowly managed to fix it with the help of the Montreal Protocol. In this post, I will be discussing a hypothetical – what would our world be like if we had never realised and tried to fix our mistake? This discussion will be based on a study done by Newman et al. (2009) which employed the use of environmental modelling to figure out these hypothetical situations.
The study aims to describe the very large ozone losses and the subsequent rise of ultraviolet (UV) levels as a result of CFC emissions. The large CFC perturbations used here lead to large chemical ozone losses and large dynamical changes that lead to large ozone changes. The study refers to these chemical and dynamical effects as ozone loses as a whole, rather than differentiating between them. The study employed the use of environmental modelling to simulate “what if” scenarios as an attempt to evaluate the effectiveness of the Montreal Protocol.
The study modelled four scenarios – “reference past” (an attempt to simulate the past observations of the atmosphere), “reference future” (an attempt to simulate the future using our best guesses for future ozone depleting substances (ODSs) and supersonic transports (SSTs)), “fixed chlorine” (with chlorine levels fixed at the 1960 level), and the “WORLD AVOIDED” (driven by one of the mixing ratio scenarios established in past literature). A summary of these scenarios can be found in the table below
Based on existing literature and past data, the researchers created multiple models to understand exactly how the Montreal Protocol has helped in fixing the ozone layer. They also produced MANY illustrations of these findings and frankly, it was hard for me to understand them at first glance. One of the figures that was more straightfoward and really highlighted how helpful the Montreal Protocol has been was Figure 3 in their report, shown below.
For me, this diagram clearly shows the difference between our current fate and what would have been had we not taken action against CFCs. The diagram clearly illustrates how large concentrations of ODSs in the atmosphere would have destroyed majority of the ozone layer by 2065. According to the researchers, this would have been a whopping >60% global annual average losses of ozone. The diagram also clearly illustrates how very large ozone losses were computed at all latitudes in the “WORLD AVOIDED” scenario. The largest losses occur in the polar latitudes, although tropical latitudes would also incur surprisingly large loses. The researchers claim that this loss in the tropics would have been a result of heterogeneous chemical processes that occur in the 2052–2058 period. This “polar chemistry” in the tropics begins to appear in the lower stratosphere as a consequence of cooling resulting from increased vertical lifting.
Overall, this was a (challenging but) very interesting read. The study provided a new perspective for me in understanding exactly how “fortunate” of a position we are currently in – in terms of ozone layer depletion specifically. Of course, other anthropogenic and natural causes have spurred other sources of global warming that we have to once again, come together and work on. The Montreal Protocol is one of the most successful international environmental agreements to date. Let’s work towards making all existing agreements and future agreements just as successful for a greener future.
Newman, P. A., Oman, L. D., Douglas, A.R., Fleming, E. L., Frith, S. M., Hurwitz, M. M., Kawa, S. R., Jackman, C. H., Krotkov, N. A., Nash, E. R., Neilsen, J. E., Pawson, S., Stolarski, R. S. & Velders, G. J. M. (2009). ‘What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated?’. Atmospheric Chemistry and Physics, 9, 2113–2128, https://doi.org/10.5194/acp-9-2113-2009, 2009.