Without the ozone layer, life as we know it would not exist. Scientists are therefore closely monitoring how the ozone layer is doing. In the past few years, two new developments have caught your attention and concern. What did they find and what does that mean? That’s what we’ll talk about today.
First things first: ozone is a molecule made up of three oxygen atoms. It is unstable and on the surface of the earth it disintegrates quickly, on average within a day or so. Because of this, there is very little ozone around us, and that’s a good thing, because breathing ozone is really unhealthy, even in small doses.
However, ozone is created when sunlight hits the upper atmosphere and accumulates up there in a region known as the “stratosphere”. This “ozone layer” then absorbs a large part of the sun’s ultraviolet light. The protection we receive from the ozone layer is extremely important as the energy of ultraviolet light is high enough to break molecular bonds. Ultraviolet light can therefore damage cells or their genetic code. This means that exposure to ultraviolet light increases the risk of cancer and other mutations significantly. I explained the radiation risk in more detail in an earlier video. More information can be found here.
You’ve probably all heard of the ozone hole, which was first discovered in the 1980s. That ozone hole is still with us today. It was caused by human emissions of ozone-depleting substances, particularly chlorofluorocarbons – CFCs for short – used in refrigerators and aerosol cans, among other things. CFCs have now been banned, but it will be at least a few more decades for the ozone layer to fully recover. With that in mind, let’s take a look at the two new developments.
The first news is that last year we saw a large and pronounced hole in the ozone layer over the North Pole, in addition to the “usual” one over the South Pole. This has happened before, but it is still an unusual occurrence. This is because the formation of an ozone hole is driven by supercooled water and nitric acid droplets that are present in polar stratospheric clouds, that is, clouds that you find at the poles in the stratosphere. But these clouds can only form when it’s cold enough, and I mean really cold, below about -108 ° F or -78 ° C. So the main reason why ozone holes form more easily over the South Pole than over the North Pole , quite simply that the South Pole is colder on average.
Why is the South Pole colder? Basically, it’s because there are fewer high mountains in the southern hemisphere than in the northern hemisphere. Because of this, wind circulations around the South Pole tend to be more stable. They can trap air, which then cools down in the dark polar winter months. In contrast, air above the North Pole mixes more efficiently with warmer air from mid-latitudes.
Occasionally, however, cold air is also trapped over the North Pole, creating conditions similar to those at the South Pole. This happened in spring 2020. In March and early April, the North Pole experienced the largest arctic ozone hole of all time for five weeks, surrounded by a stable wind circulation known as the polar vortex.
Now, over the past decade, we’ve all seen climate change changing wind patterns in the northern hemisphere, resulting in prolonged heat waves in summer. This begs the question of whether climate change was one of the factors that contributed to the northern ozone hole, and therefore whether we should expect it to become a recurring event.
This question was recently explored in an article by Martin Dameris and co-authors. For the full reference, see the information below the video. Their conclusion is that observations of the northern ozone hole are so far only a coincidence. However, when coincidences pile up, they create a trend. And so the researchers are now waiting to see whether the hole will return in spring 2021 or in the coming years.
The second new development is that the ozone layer over the equator is not recovering as quickly as the scientists expected. Above the equator, the amount of ozone in the lower parts of the stratosphere appears to be decreasing, although this trend will be offset for the time being by the expected ozone recovery in the upper parts of the stratosphere.
The scientists working on it previously considered a number of possible reasons, from data problems to illegal emissions of ozone-depleting substances. But the data held up, and while we now know that illegal emissions are indeed occurring, those are not enough to explain the observations.
Instead, further analysis suggests that ozone depletion in the lower stratosphere above the equator again appears to be driven by wind patterns. Earth’s ozone is itself generated by sunlight, which is why most of it forms over the equator, where sunlight is most intense. The ozone is then transported from the equatorial regions to the poles through a wind cycle known as the “Brewer-Dobsonian Circulation”. The air rises above the equator and falls again in mid to high latitudes. With global warming, this circulation can become more intense, so that more ozone is redistributed from the equator to higher latitudes.
But here, too, the strength of this circulation changes randomly. It is therefore currently unclear whether the observations only show a temporary fluctuation or indicate a trend. A current analysis of various climate-chemical models by Simone Dietmüller et al shows that man-made carbon dioxide emissions are contributing to the trend of less ozone over the equator and more ozone in the mid-latitudes, and the trend is therefore likely to continue. However, I must warn you that this paper has not yet passed peer review.
Before we talk about what all of this means, I want to thank my level four supporters at Patreon. Your help will be gladly taken. And you too can help us produce videos by supporting us on Patreon. Now let’s talk about what this news from the ozone layer means.
You can say, ah, so what. Tell people in the tropics to put on more sunscreen and those in Europe to take more vitamin D. This is a science channel and I am not going to tell anyone what to worry about or not, it is your personal business. But to help you assess the current situation, let me tell you an interesting piece of history.
The 1987 Montreal Protocol, which regulates the leakage of ozone-depleting substances, was quickly adopted after the first ozone hole was discovered. It is often hailed as an environmental conservation milestone, the best example that everyone points out on how to do it right. But I think the Montreal Protocol teaches us a very different lesson.
That’s because scientists knew back in the 1970s, long before the first ozone hole was discovered, that chlorofluorocarbons would deplete the ozone layer. But they thought the effect would be slow and global. When the British Antarctic Survey discovered the ozone hole over the South Pole in 1985, it was a complete surprise.
In fact, it was later found that American satellites had measured the ozone hole years before the UK survey, but because the data was so far from what was expected, the software automatically overwritten it.
The problem was that at the time the impact of the polar stratospheric clouds on the ozone layer was poorly understood and the real-world situation turned out to be far worse than scientists thought.
For me, the lesson from the Montreal Protocol is that we would be stupid to believe that we now have all the parts to understand our planet’s climate system. We know we are driving the planet into regimes that scientists poorly understand, and chances are that this will bring more unpleasant surprises.
What do these changes in the ozone layer mean? They mean we have to pay close attention to what is happening.