Misconception Monday: Oh No! Ozone Hole
Stephanie Keep, who normally leads Misconception Monday, is kindly allowing me to guest-spot while she's up to her eyeballs in epigenetics. I thought I’d take this opportunity to highight one of the most common mix-ups involving climate change: conflating the human-caused ozone hole with human-induced impacts on the climate system.
There actually are connections, but not the ones people normally think.
Misconception: The hole in the ozone, caused by chemicals in hairspray and the manufacturing of Styrofoam cups, is responsible for global warming because it has allowed more heat from the sun to enter Earth's atmosphere.
Correction: Recent climate change has been primarily caused by human consumption of fossil fuels, which when burned release heat-trapping chemicals into the atmosphere.
And, we might add, the problematic chemicals in hairspray and Styrofoam cups have long been banned due to the Montreal Protocol, so they have an alibi for anthropogenic climate change. More on that in a minute.
But first, let's take a step back and look at how we think of the atmosphere.
Like fish at the bottom of an ocean of air, humans are generally oblivious to the fact that the air surrounding us has mass and layers. We also rarely consider how thin the atmosphere is: the troposphere, where the vast majority of air's mass and water vapour are located, extends to only about ten miles above us. In polar regions, it's often only four miles up.
The stratosphere, which extends another thirty miles up, is where the ozone layer is located, generally in the lower region. Also known as the "ozone shield" because it blocks some of the mutation-inducing UV radiation from reaching the surface of the Earth, the ozone layer varies in depth and thickness depending on location and season.
How is it that the ozone hole and climate change have become blurred and conflated in people's minds? Easily.
Both involve human-generated chemicals in the atmosphere. And both tend to be skimmed or skipped over in science classes. When I taught introduction to Environmental Science twenty years ago at a community college, the two topics were lumped together in one of the last chapters of a thirty-six chapter textbook. I got to spend all of twenty mintues on both topics.
But even if the topics are covered, it's still all too easy to get them confused. The ozone "hole" led to increased incidence of sunburn and skin cancer. So could the hole also be letting through more heat from the sun, thereby warming the planet? Why not? Seems like a no-brainer.
Understanding (and teaching about) the real mechanisms and processes behind climate change, on the other hand, is far more complicted and less intuitive if one goes beyond the "blanket" or "greenhouse" models which are both convenient but scientifically flawed. Here is the beginning of a scientific explanation:
Incoming shortwave photons from the sun enter Earth's atmosphere. Some are filtered or reflected, most are absorbed and re-radiated by Earth's surface as outgoing longwave, infrared photons. These photons resonate with certain gases in the atmosphere that then absorb and re-radiate the energy, adding more of it to the climate system rather than venting it to space. Greater concentrations of these gases that trap infrared result in increased heating of the planet. (And at this point, what most people are hearing is blah, blah, blah.)
So, how can we tempt people away from the very intuitive, but very wrong idea of a hole in the ozone heating Earth up? Michael Ranney and his colleagues at UC Berkeley have tried several ways of conveying the basics through short and long-form videos. But since this non-intuitive, complicated mechanisim of the greenhouse effect is often not taught—and isn't even covered in the Next Generation Science Standards—it is no wonder that people default to the simplist explanation: big, bad hole is letting in more energy from Sun and warming planet.
We've previously delved deeply into the carbon cycle and greenhouse effect as a key and fundamental concept for climate literacy, but perhaps while we are talking about it, maybe it's a good opportunity to review what ozone is.
Ozone (O3) is a molecule that contains three oxygen atoms. Depending on where it's situated in the atmosphere and how much of it there is, it can be "good" or "bad" in terms of life on Earth. Ozone that occurs close to the ground as part of smog is "bad" ozone—a pollutant that mixes with other forms of pollution in the lower atmosphere causing irritation to the eyes and lungs.
On smoggy days, “ozone alerts” are common in many large cities. It is also a greenhouse gas when it occurs in the troposphere, trapping heat from outgoing infrared photons, as do water vapor, methane, carbon dioxide, and other greenhouse gases.
"Good" ozone exists as a thin layer in the lower stratosphere, roughly 12 to 19 miles above Earth, varying seasonally and by location. At this altitude, ozone absorbs ultraviolet (UV) radiation coming from the sun and thus protects organisms from receiving too much of this energy that can cause skin cancer and other mutations. The ozone “hole” occurs when human-made chemicals, primarily chlorofluorocarbons (CFCs) used in refrigeration, interact with and destroy the stratospheric ozone.
The international Montreal Protocol, signed in 1987, banned most harmful CFCs and has been largely successful at preventing continued deterioration of the protective ozone layer. However, people living in Australia and New Zealand, where the ozone hole has historically been most noticeable, must continue to be cautious and protect themselves from sun exposure.
But ironically, a few of the "super" greenhouse gases such as hydrofluorocarbons (HFCs), which are much more powerful at trapping longwave infrared light than carbon dioxide, were created in laboratories specifically to replace the banned CFCs. The law of unintended effects in play. (Note: there are ongoing efforts to cut HFCs; go here for more.)
Countering the confusion requires first covering the essentials of both, which is often not done or done well, and then stressing they are different but in a sense related since both result from human activities, specifically venting certain gases into the atmosphere.
This is not to say there is absolutely no relationship between the problems with the ozone layer and global climate change. As Jeff Masters of Weather Underground writes:
The enhanced greenhouse effect that we're seeing due to a man-made increase in greenhouse gases is acting to warm the troposphere and cool the stratosphere. Colder than normal temperatures in this layer act to deplete ozone. So the cooling in the stratosphere due to global warming will enhance the ozone holes in Arctic and Antarctic. At the same time, as ozone decreases in the stratosphere, the temperature in the layer cools down even more, which will lead to more ozone depletion. This is what's called a "positive feedback."
And as we know, positive feedbacks are not necessarily good.