From victim to perpetrator: how ozone harms the ocean’s climate cooling ability
Environment Climate Change Ozone layer

From victim to perpetrator: how ozone harms the ocean’s climate cooling ability

Endre Szvetnik
Endre Szvetnik

In 10 seconds? Researchers have discovered how ozone (O3) concentrations have contributed to global warming in the Southern Hemisphere. The increasing levels of the gas in the lower levels of the atmospherewere found to weaken an important cooling mechanism.

What? Ozone is now the bad boy? To simplify it, ozone is good in the upper, stratospheric part of the atmosphere (5-10 km above the surface) because it protects us from the UV rays of the Sun and bad in the lower, tropospheric part (up to 5 km above the surface). This is because it lets the top layer of the sea to warm up. According to a recent study, over the last 70 years ozone levels in the upper part of the atmosphere dropped and increased in the near-surface part over the Southern Ocean (aka the Antarctic Ocean). That made the top 2km layer of the ocean warm up faster than previously thought – the paper says.

And it matters because… our oceans are acting as ‘heat sinks’, slowing down global warming by absorbing greenhouse gases, chlorofluorocarbon gases (CFCs, ironically, responsible for destroying the ozone layer in the upper part of the atmosphere) and heat. However, the concentration of ozone in the lower part of the atmosphere accelerates sea temperature rise. That, in turn affects oceanic winds and currents. As the water’s movement slows down, the ocean’s ability to act as a heat sink is reduced. More ozone in the near-surface part of the atmosphere contributes to this process. In addition, high ozone levels are harmful for people with asthma and toxic for plants, cutting yields and harming forests.

OK and what’s the cause? Surprise, surprise—human activity. More precisely: air pollutants, like hydrocarbons and especially, nitrogen oxides from our cars and industry, with the petrochemical industry sitting on top. Near-surface ozone is created through reactions of such pollutants and so called volatile organic compounds (VOCs), often man-made chemicals, for example, solvents. (More on how powerplants can be involved in the process.)

Changes in ozone levels with altitude in the tropics. Most ozone resides in the stratoshperic ozone layer (red line) and the vertical extent or thickness of this layer varies from region to region and with the changing seasons. Source: United Nations Enrvironment Programme
Changes in ozone levels with altitude in the tropics. Most ozone resides in the stratoshperic ozone layer (red line) and the vertical extent or thickness of this layer varies from region to region and with the changing seasons. Source: United Nations Enrvironment Programme

How did research find the role of ozone in global warming? We’ve known for a while that ozone concentrations in the lower part of the atmosphere can affect the oceans but estimates were more modest. The team involved in the current paper studied the relationship between ozone concentration and the ocean’s cooling potential by using models to simulate the changes in ozone levels between 1955 and 2000 and by excluding factors that could have biased the results. This is how they’ve found that ozone has decreased in the upper atmosphere and increased in the lower part of the atmosphere. Another sobering find is that this change was responsible for 60% of warming caused by ozone levels, which surpassed previous estimates.

So, what can be done? The study highlights the connection between environmental pollution and climate change, so it’s not just greenhouse gases that are the villains of the piece. In other words, while focusing on cutting back on the use of fossil fuels and compensating for their climate-warming, we also need to act on the causes of air pollution that also contributes to the process. In the US, the Clean Air Act sets standards for levels of ‘criteria air pollutants’, including ozone. Now there is another challenge for policymakers and society to reduce the emission of tropospheric ozone-creating pollutants on top of costly climate action. To complicate things, surface ozone levels in a geographic region can depend on emissions (by up to 30%, according to this study) in other regions, so international cooperation is required to tackle the issue.


Remember the fears over the ozone hole?

Well, you wouldn’t if you were not alive in the 1980 and 90s. British researcher, Jonathan Shanklin and his colleagues, posted to an Antarctic research station, started to notice in the 1970 the thinning of the ozone layer above them.

The ‘ozone hole’ – as it was called in popular imagination caused worldwide alarm because of fears how unhindered UV radiation would affect life. Researchers have discovered that CFC gases were harming the ozone layer (bagging a Noble Prize in chemistry) but they had a fight on their hands with industry.

Still, governments were forced to act. The result was the Montreal Protocol of 1987, an agreement to phase out and cut out the use of ozone layer-depleting substances, among others chlorofluorocarbons, or CFC gases used in refrigerators, aerosol sprays, solvents and packaging materials. This is the only international treaty that all countries have ratified.

According to scientific estimates the “ozone hole” will disappear around 2050.

Endre Szvetnik has distilled 8 research papers, saving you 28 hours of reading time.




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