There’s a Hole in the Ozone Layer, Dear Liza, Dear Liza

A blog about the human impacts on Antarctica would be incomplete without a post or two concerning the hole in the ozone layer. This is perhaps the most well-known human impact on the continent. Furthermore, this blog has so far considered the human impacts on the ground or on the marine environment. The atmospheric effects are also significant. 

The ozone layer lies between the stratosphere and the troposphere. The reason this layer is useful to us is that ozone molecules absorb ultraviolet (UV) radiation from the Sun and therefore protect us from the harmful effects of excessive UV radiation exposure (Martin and Hine, 2014, in ‘A Dictionary of Biology’).

The hole in the ozone layer was discovered by Farman et al. (1985). The authors collected data at the Halley Bay research station from 1957 to 1984 and, by using spectrophotometers, discovered that the ozone layer was depleting in spring (which is from September to November). The cause of ozone depletion was found to be a chemical reaction that occurs between chlorine and bromine atoms, that originate from chlorofluorocarbons, and ozone (Molina and Rowland, 1974). Chlorofluorocarbons (CFCs) were invented in the 1920s and commercially manufactured in the 1930s (The Ozone Hole, 2014). CFCs were used as cleaning solvents, in fire extinguishers, in aerosols and as refrigerants in air conditioning units (Tsai, 2014:883, in ‘Encyclopedia of Toxicology’). They were desirable because they possessed beneficial properties, including the fact that they were nontoxic and non-flammable. 

Molina and Rowland found that the reaction takes place in the presence of UV radiation. According to the NOAA (2008), during the Antarctic winter, ‘stratospheric ice clouds (PSCs, polar stratospheric clouds) form when temperatures drop below -78C. These clouds are responsible for chemical changes that promote production of chemically active chlorine and bromine’. During the winter, there is no sunlight in Antarctica. Thus, when spring arrives and the sun appears, chlorine and bromine molecules react with ozone molecules, causing it to break down. This is what creates a hole in the ozone layer during the spring. The reason why Antarctica in particular is subject to ozone depletion more than, say, the Arctic, is that cold temperatures are required for the reaction (Solomon, 2004). Figure 1 shows the monthly mean total ozone levels at Halley Bay in October, the middle of spring when ozone depletion occurs, from 1957 to 1984. The figure shows spring ozone depletion starting from the mid-1960s. CFCs have caused the ozone layer to deplete by as much as 50% (Smith et al. 1992) not just in spring, but in the winter as well (Rowland, 1986). The human invention of CFCs has therefore been the sole contribution to ozone depletion. 

Figure 1. Monthly mean total ozone levels at Halley Bay in October from 1957 to 1984. Source: Farman et al. (1985)

Effects

Without the protective shield from the ozone layer, more UV radiation reaches the Earth. For humans, greater exposure to UV can have severe health effects, such as increasing the likelihood of developing skin cancer (Norval et al. 2011), damage to DNA (Herrlich et al. 1992) and eye damage (Longstreth et al. 1995).

But I think it would be more relevant to focus on the effects of ozone depletion on species living in Antarctica. For instance, it has been observed that marine phytoplankton and diatoms have experienced DNA damage due to greater UV exposure (Buma et al. 2001). Furthermore, Smith et al. (1992) discovered that, in the Bellingshausen Sea (for a map of its location, see this post), a greater concentration of UV radiation is hindering photosynthesis which in turn is preventing the growth of phytoplankton. These findings illustrate how the marine ecosystem is negatively affected by the hole in the ozone layer. More specifically, phytoplankton is affected negatively. The importance of phytoplankton is illustrated by the food chain from my post from 29 November. Krill and penguins feed on phytoplankton. This shows how ozone depletion affects the food chain and therefore causes a change in the marine ecology of Antarctica. Additionally, this highlights that although ozone depletion happens in the stratosphere, there are indirect terrestrial effects observed as well.

Figure 2. Marine phytoplankton

I shall end this post with a short video to summarise the hole in the ozone layer, i.e. the key findings, the mechanism, the treaty…etc. It is presented by Shanklin, who co-discovered the hole in the ozone layer.

Next week, I will explore the subsequent regulation that followed from this discovery and its success at restoring the ozone layer. The updated score is 7-4, negative impacts seem to be taking the lead!