Why Has the Ozone Layer Continued to Deplete?

I've taken an eight-week break from blogging.  It's been the first long break since I began the blog in 2010.  The absence is owed not to having little to write about, but rather to having so little time to write it in.

Today, I'd like to write about an often misunderstood phenomenon: ozone layer depletion.

In my experience, the public at large believes that climate change and ozone layer depletion are very much connected, when in fact, the two are independent threats to life as we know it on Earth. 

Climate change, a.k.a. global warming, is a gradual increase in the average temperature of Earth's atmosphere brought about by the greenhouse effect, whereby certain gases, like carbon dioxide and methane, trap heat in the atmosphere.  Global warming is a much larger problem than ozone layer depletion as it can set off a multitude of other changes to our biosphere and it will be far more difficult to avoid.  It is in many ways the grim story of the 20th century that will inevitably haunt the 21st.

The fact that ozone layer depletion will not haunt us too badly in the 21st century and beyond is truly a success story.  It is a rare example where mankind acted responsibly as a species for our own preservation.

The summary of the science is that ozone molecules, which congregate in a 3 km belt roughly 10 km from the Earth's surface, dramatically reduce the quantity of the Sun's ultraviolet rays that reaches us.  These rays damage skin cells and over-exposure to them leads to skin cancer.

In the late twentieth century, it was observed that certain areas of the ozone layer were depleting at an alarming rate.  The cause of it: chlorofluorocarbons (CFCs) released into the atmosphere.  These chemicals, consisting of one or two carbons, some chlorine and some fluorine (as the name suggests) were widely used as refrigerants throughout much of the twentieth century.  The problem is that they cause ozone molecules to decompose.  Incidentally, CFCs also happen to be potent greenhouse gases, so this may be one reason why the climate change/ozone depletion confusion has permeated society.

The 1987 Montreal Protocol called for drastic reduction in the production of CFCs in response to ozone layer depletion.  While this treaty was largely adhered to, the ozone layer continued to deplete and is worse today than it was then.  The principal reason for this is that CFCs have a huge lifespan upwards of fifty years.  So, while we no longer emit vast quantities of the banned substance, we continue to pay for our mistakes of yesterday.  All systems have inertia, and a large one, like a planet-sized shell of molecules, has a lot of it.  There is a huge lag between cause and effect.

Indeed, UV levels and skin cancer rates are expected to continually climb over the coming decades.  But, because of our collective responsible action a few decades ago, the ozone layer will begin to return to its pre-CFC state shortly thereafter.  It is refreshing to feel proud of our world leaders;  the ozone layer story is my go-to example when I want to express that "our leaders are not all bad."

Sadly, man-made climate change is not as simple a foe as ozone layer depletion.  A simple chemical swap will not solve this one.  Sweeping global change on how we produce energy will need to take effect, and soon.  The magnitude of the task is disconcerting to say the least and I am not confident that we will confront this problem before it completely overwhelms us.  But then, I think of how we reacted responsibly when faced with ozone layer depletion, and it offers a glimmer of hope.

So, there you have it.  I told one of my students that I would blog on this topic some months back, and finally got around to it.  I'm back, baby!