Climate Primer #2: The First Planetary Boundary – Stratospheric Ozone Depletion

To summarize yesterday’s post, “Climate Primer #1: Greenhouse Gases,” energy reaches the Earth from the Sun. Some fraction of it is reflected from (or absorbed and reemitted by) the different features of the Earth’s surface. Owing to the molecular structure of greenhouse gases, when present in the Earth’s atmosphere, these compounds trap some of that reflected (or reemitted) energy. A key factor regulating the Earth’s climate is the fraction of the incident solar energy reaching our planet that remains trapped within the confines of the atmosphere, so as the concentrations of greenhouse gases – such as carbon dioxide, methane, nitrous oxide, many human-made halogenated compounds, and water vapor – rise in the atmosphere, the planet will tend to heat up in direct proportion, barring the presence of other mitigating factors (such as, say, a huge amount of volcanic ash or nuclear-winter fallout “blanketing” the Earth).

In view of these facts, talk, in recent decades, has been of global warming, climate changing, anthropogenic climate disruption, climate crisis, and climate emergency; however, what is, in fact, unfolding at present is a comprehensive crisis of the life-sustaining capacity of the Earth, of which climate change is only one element. For this reason, people (including Greta Thunberg) speak of the simultaneous climate and ecological crises, but – as with certain other efforts at inclusion – attempts to encompass all the various components of a complex phenomenon in a single phrase or acronym often lead to ungainly neologisms, so for simplicity, I will continue to use “climate crisis” by which I mean, as I wrote yesterday, “the manifold intersecting phenomena that now accelerate the Earth system towards broaching of key planetary boundaries” within which it is necessary to remain to sustain (human) life.

I thought it would be useful to summarize the key planetary boundaries. To that end, I draw on the Stockholm Resilience Centre (across which, I’d come before, but to which I’ve most recently been directed by Ann Pettifor’s worthwhile book, The Case for the Green New Deal) which offers a schema of nine key boundaries. (One could easily imagine other taxonomies, but I think theirs works.) Hence, the next nine posts here will quote directly from SRC’s schema, with some of my own commentary added on.

With no further ado, Planetary Boundary #1 – Stratospheric Ozone Depletion, as defined by the SRC:

The stratospheric ozone layer in the atmosphere filters out ultraviolet (UV) radiation from the sun. If this layer decreases, increasing amounts of UV radiation will reach ground level. This can cause a higher incidence of skin cancer in humans as well as damage to terrestrial and marine biological systems. The appearance of the Antarctic ozone hole was proof that increased concentrations of anthropogenic ozone-depleting chemical substances, interacting with polar stratospheric clouds, had passed a threshold and moved the Antarctic stratosphere into a new regime. Fortunately, because of the actions taken as a result of the Montreal Protocol, we appear to be on the path that will allow us to stay within this boundary.

Nice to start with some good news! For today’s bonus recommendations – and more good news – two Nature Climate Change articles, one, which offers some ground for guarded optimism regarding the prospect for rapid shift towards acceptance of the seriousness of climate crisis among conservatives in the US, and another, which offers evidence that past climate models have significantly overstated the amount of methane likely to be emitted by melting permafrost.