On September 22 (right), the hole in the ozone layer (blue and purple) above Antarctica reached its smallest maximum size in two decades, covering 21.2 million square kilometers. The largest ozone hole on record occurred on September 9, 2000 (left), measuring 29.9 million square kilometers. Credit: GSFC/NASA
On September 22 (right), the hole in the ozone layer (blue and purple) above Antarctica reached its smallest maximum size in two decades, covering 21.2 million square kilometers. The largest ozone hole on record occurred on September 9, 2000 (left), measuring 29.9 million square kilometers. Credit: GSFC/NASA

By Claire

I find that a lot of the time, I am quite negative when it comes to the prospects for future climate change. Most of my posts are quite pessimistic about the chances of reaching a global agreement on limiting carbon emissions in time to make any kind of significant impact on global temperatures. But, honestly, that’s what I believe, and it gets pretty depressing when I start to think about what our future might look like.

BUT… there is hope.

One great success story of the possibilities of global action to stem environmental degradation is that of the ozone hole. 

Now, before I go any further, I feel that I really need to say that the ozone hole is not a product of climate change. I quite often hear people lumping global warming and the hole in the ozone layer into the same sentence. They are two completely different issues – climate change being caused by carbon dioxide, and the ozone hole being caused by CFCs.

So, really simply, CFCs (a.k.a. chlorofluorocarbons) are a man-made chemical, made up of chlorine (Cl), flourine (F) and carbon (C). They were most commonly used in refrigerators and as aerosol propellants. CFCs are relatively unreactive chemicals, which is what made them so popular and widely used. Unfortunately, it was this property that also made them so harmful to ozone.

ozone_depletionWhen CFCs are released from these products, they are able to travel up into the stratosphere, where the ozone layer is situated. Here, the molecule is broken apart by UV light, to produce a free Cl atom:

CFCl3 + electromagnetic radiation → CFCl2 + Cl

This free Cl atom is very reactive, and unfortunately, it is ozone that it reacts with. Ozone is made up of three Oxygen (O) atoms (O3).

Cl + O3 → ClO + O2: The chlorine atom changes an ozone molecule to ordinary oxygen

ClO + O3 → Cl + 2 O2: The ClO from the previous reaction destroys a second ozone molecule and recreates the original chlorine atom, which can repeat the first reaction and continue to destroy ozone.

And so the cycle continues. A single CFC molecule can destroy as many as 100,000 ozone molecules, which has devastating impacts on the ozone layer, creating the hole we currently see over Antarctica.

So that was the problem. Human production and use of CFCs was creating a hole in the ozone layer.

What needed to happen was a reduction and eventual stop in the use of CFCs. And that’s exactly what happened.

Measured and projected CFC abundance in the atmosphere.
Measured and projected CFC abundance in the atmosphere.

Enter the Montreal Protocol. The Montreal Protocol is a global agreement to phase out the use of CFCs in order to limit the destruction of the ozone layer. The Protocol was opened in 1987  and put into force in 1989. CFCs were gradually phased out during the first two stages of the agreement, and were effectively banned in 1996.

The Montreal Protocol is hailed as the most successful international agreement to date.

Observations of the ozone hole taken last year indicate that it was at its smallest maximum extent since 1990. This is largely due to warmer temperatures seen over Antarctica, which help to limit the destructive properties of CFCs. The hole is projected to have completely disappeared by 2050.

So although the outlook for a global agreement on reducing carbon emission doesn’t currently look good, history tells us that the world is able to come together to address large-scale environmental issues, and I for one, am going to use that as a source of hope.