Ozone Depletion and Global Warming

A teacher colleague was speaking to me the other day, and she said that many of her students, high school, were confused about the terms and concept of the ozone layer and the carbon dioxide-global warming debate, including mixing up the two. Although they are related, there are separate issues involved.

Let’s take a look at these two issues… The ozone layer debate surfaced in the late 70s as satellite information revealed a large hole in the ozone layer over both of earth’s poles. What is ozone, and what does it do? Ozone is a special form of oxygen, written chemically as O3 . Normal oxygen, the kind we breathe, is shown as O2 . At ground level, ozone is bad news, because it is very reactive and contributes significantly to the formation of smog. Ozone is generated by internal combustion engines and other industrial processes and by lightning. In space, on the outer edge of the atmosphere, however, ozone serves the very useful purpose of protecting the surface of the earth from harmful ultra-violet (UV) rays from the sun. The ozone layer is not very thick, I have read as thin as a few centimetres, but it absorbs these UV rays nicely.

These holes that were found turned out to be caused by the reaction between ozone and chlorofluorocarbons, more commonly known as Freons®. These compounds were used extensively in aerosol propellants, refrigerators and air conditioners and plastic foaming agents, from which they easily escaped into the atmosphere.

In 1987, most countries, including Canada, signed the Montreal Protocol, in which they pledged to drastically reduce the amount of Freons used, and switch, where possible, to less ozone-damaging substitutes. This process has, over the last fifteen years or so, had the desired effect and damage to the ozone layer has been lowered considerably. Although gains have been made we must maintain our efforts.

This was the reason for the increased awareness of the need for sunscreen, especially in northern latitudes.

Now to the carbon dioxide issue, or Global Warming 101. Most of our industrial processes throughout the world, including transportation, power generation, manufacturing, and many others, rely on fuel to keep going, and mostly this fuel is something that is burned. It used to be wood, then (and still) coal, oil, natural gas, and of course gasoline and diesel fuel. Burning these fuels produces carbon dioxide, lots of it, about the same mass as the fuel burned. In pre-industrial times, there was about 200 ppm (parts per million) carbon dioxide in the earth’s atmosphere. It began to increase in the 19 century, shot up in the 20th, until we are currently looking at almost 300 ppm. This may not sound like much, and you and I can go about our daily lives not noticing any difference.

There are several other gases that contribute to the warming process, most of which are by-products of human activity, but carbon dioxide is the largest single contributor.

However, here is where it gets interesting… you know what a greenhouse is: an enclosed structure covered with glass panels. As sunlight passes through the glass, it is reflected back by the plants, wood and dirt within the greenhouse but at a longer wavelength that does not pass back out through the glass. The air inside the greenhouse becomes much warmer… good for the plants. As sunlight passes through the earth’s atmosphere, the higher carbon dioxide level in the atmosphere has the same effect as the glass panels on the greenhouse, preventing a large portion of the sunlight from being reflected out into space, and thereby warming the atmosphere. In February in Ontario, we may think this is a good thing, but we would be wrong. Significant changes in the atmosphere, including the increase in carbon dioxide and the other “greenhouse gases” can have very severe consequences to rainfall, snowfall, glacier formation, sea levels, sea ice thickness and duration to name a few. These in turn have huge consequences for agriculture. We won’t be growing bananas in Brockville any time soon, but if the places where bananas are grown today become deserts or are flooded by seawater, we have a problem. As well, many millions of people live within a few metres of sea level, so any rise will have catastrophic consequences for them as well as us. (Brockville is about 300 ft. above sea level, depending on where you are in the city).

We will take a look at some of these in more detail in another column, but my point today is that the ozone layer depletion problem, while not solved, is well understood and means are being implemented to address it. The global warming problem appears, by all scientific analysis, to be related to increasing carbon dioxide in the atmosphere, but because we seem to be wedded to carbon-based fuels, and with the industrial intensification in China and India, and the denial by many nations, businesses and individuals that there is a genuine problem, no near term lowering of carbon dioxide is likely.

Recent research has shown that the ozone-depleting chemicals, which we know have been significantly reduced in the last two decades, were also major contributors to global warming, so their reduction or elimination has had a very positive effect in countering global warming.

So, ozone and global warming: two different but interconnected problems, two different but interconnected causes, two (at least) different solutions.