Posts Tagged ‘Antarctica’
Antarctica, global warming and our endless complacency
The most recent New Scientist podcast has reported from a big meetup re global warming, melting ice, disappearing islands and such, and I feel that’s something I need to know much more about. The Australian Antarctic Research Conference was just held in Hobart in late November, attended by some 500 researchers.
So here’s the grim. According to an interviewee who attended the conference, ‘there was a precipitous drop-off in the extent of the winter sea-ice around Antarctica in 2023 and again in 2024, 2024 being nearly as bad as 2023’. The 2023 data for winter sea-ice was the lowest with regard to expectations since data has been recorded. Seven standard deviations off the mean, apparently. Whateva, that doesn’t sound good. So the decrease in Antarctic sea-ice over this past decade is equivalent to that in the whole Northern Hemisphere in the past 45 years. And if those magnitudes continue, the Antarctic could be free of summer sea-ice even before the Arctic, which is expected to experience that scenario by around 2050.
So this will certainly lead to changes in ocean currents, and other mostly unpredictable knock-on effects, supposing the changes being measured down south represent something permanent. The fall in sea-ice became measurable from 2016, but has become more dramatic recently. Ice reflects sunlight back into space, so its reduction will lead to oceanic warming, which in turn will lead to a more rapid reduction of ice. One of the key areas of concern is the Denman Glacier and the surrounding Shackleton Ice Shelf, which is melting quite quickly. The complete melting of that particular system is calculated to lead to some 1.5 metres of global sea level rise (which seems hard to believe, I must say).
So what is to be done, and how are those most responsible for the global warming that’s causing all this, responding? Well, it doesn’t seem to be getting much airplay on the internet at present, and apart from New Scientist, there hasn’t been much reporting on the above-mentioned conference and its findings, so I’m having to dig deeper.
I’ve picked up a new term: the cryosphere. That’s the Earth’s icey stuff, in all its forms and habitats. And of course most of it exists at or near the Poles. The IPCC released a Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) in September 2019, all available online, and chapter 4, ‘Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities’, is obviously of particular interest. It found that the dominant cause of the rise in global mean sea level (GMSL), at least since 1970, is ‘anthropogenic forcing’, which presumably means something like ‘humanity’s typically forceful influence’. It also found the GMSL rise is accelerating. The situation was worse in the past, though. Way back in the last interglacial, some 120,000 years ago, and also on other occasions millions of years ago, but there were a few H sapiens and other hominins around at the time of the last interglacial, and they obviously survived, so why worry?
Seriously the effects of sea level rise (SLR) on coastal communities are enormously complex and multifaceted, with human-induced habitat degradation muddying the waters of coastal ecosystems, so to speak. There are obvious reasons why humanity tends to congregate around coastal regions – and it’s particularly obvious why it happens here in Australia – and where humanity congregates in large numbers, there’s bound to be a cost, in particular to other species, with rebound effects. Here’s how the IPCC puts it:
Coastal ecosystems, including saltmarshes, mangroves, vegetated dunes and sandy beaches, can build vertically and expand laterally in response to SLR, though this capacity varies across sites … These ecosystems provide important services that include coastal protection and habitat for diverse biota. However, as a consequence of human actions that fragment wetland habitats and restrict landward migration, coastal ecosystems progressively lose their ability to adapt to climate-induced changes and provide ecosystem services, including acting as protective barriers….
Again, this doesn’t sound like deadly serious stuff, to selfish humans like us, but global SLR, estimated by the IPCC to be around 3.3 mm annually (and likely set to increase), will clearly affect islands and coastal regions worldwide. It’s also important to note that global warming isn’t occurring uniformly – Africa’s Central Sahel region, effectively the Sahara Desert, is warming at 1.5 times the global rate. War-torn regions such as Syria and the DRC are also more vulnerable to climate change. Afghanistan is now experiencing its worst drought in decades, while paradoxically there is severe flood damage in some areas. Lack of foreign aid due to the Taliban takeover has created an economic and humanitarian crisis there.
Finally, to focus more on Australia, our future scenario depends muchly on global greenhouse gas emissions, and we, globally, have done little, in spite of all the fuss, to reduce these emissions. The levels reached a new high in 2023, with CO2 ‘accumulating in the atmosphere faster than any time experienced during human existence, rising by more than 10% in just two decades’, according to a report from the World Meteorological Organisation (WMO). Sea level rise is more of a factor here than in most regions – 85% of our population now lives within 50 km of the coast. This will of course affect coastal infrastructure and our celebrated beaches, but the real issue, for Australia and elsewhere, is that the fact that previous records are ‘falling like dominoes’, according to one expert, is still not being taken seriously enough by the major contributors to the problem, both on a corporate and national level. Australia’s native islander peoples, in the Torres Strait and elsewhere, are facing threats to their very way of life due to sea level rise, but most Australians don’t feel much affected, and many are in denial about the issue, like frogs in the proverbial warming pot.
So, what more to say? It’s hard to keep watching this all happening…
References
https://www.newscientist.com/podcasts/
https://wmo.int/news/media-centre/greenhouse-gas-concentrations-surge-again-new-record-2023
https://www.rescue.org/article/10-countries-risk-climate-disaster
about ozone, its production and depletion
People will remember the ‘hole in the ozone’ issue that came up in the eighties I think, and investigators found that it was all down to CFCs, which were quite quickly banned, and then everything was hunky dory….
Or that’s how I vaguely recall it. Time to take a much closer look.
I take my cue from ‘An ancient ozone catastrophe?’, chapter 4 of David Beerling’s The emerald planet, in which he looks at the evidence for a previous ozone disaster and its possible relation to the great Permian extinction of 252 millions years ago. I’ll probe into that matter in another post. In this post I’ll try to answer some more basic questions – what is ozone, where is the ozone layer and why does it have a hole in it?
Ozone is also known as trioxygen, which gives a handy clue to its structure. Oxygen can exist in different allotropes or molecular structures which are more or less stable. O3, ozone, is much less stable than O2 and has a very pungent chlorine-like odour and a pale blue colour. It’s present in minute quantities throughout the atmosphere but is most concentrated in the lower part of the stratosphere, 20 to 30 kilometres above the Earth’s surface. This region is called the ozone layer, or ozone shield, though it’s still not particularly dense with ozone, and that density varies geographically and seasonally. Ozone’s instability means that it doesn’t last long, and has to be replenished continually.
In 1928 chlorofluorocarbons (CFCs) were developed as a seemingly safe form of refrigerant, which, under patent as Freon, came to be used in air-conditioners, fridges, hair-sprays and a variety of other products. As it turned out, these CFCs aren’t so harmless when they reach the upper atmosphere, where the chlorine reacts with ozone to form chlorine monoxide (ClO), and regular O2. This reaction is activated by ultraviolet radiation, which then breaks up the unstable ClO, leaving the chlorine to react with more ozone in a continuing cycle.
By the eighties, it had become clear that something was going wrong with the ozone layer. Studies revealed that a gigantic hole in the layer had opened up over Antarctica, and without going into detail, CFCs were found to be largely responsible. There was the usual fight with vested business interests, but in 1987 the Montreal protocol against the use of ozone-depleting substances (ODS) was drawn up, a landmark agreement which has been successful in starting off the long and far from completed process of repair of the ozone shield.
As a very effective oxidant, ozone has many commercial applications, but the same oxidising property makes it a danger to plant and animal tissue. Much better for us to keep most of it up above the troposphere, where its ability to absorb UV radiation has made it virtually essential for maintaining healthy life on Earth’s surface.
So here are some questions. Why does ozone proliferate particularly at the top of the troposphere, in the lower stratosphere? If it’s so reactive, how does it maintain itself at a particular rate? Has the thinning or reduction of that layer seriously influenced life on Earth in the past? From my reading, mainly of Beerling, I think I can answer the first two questions. The third question, which Beerling explores in the above-mentioned chapter of his book, is more speculative, and more interesting.
Sidney Chapman, a brilliant geophysicist and mathematician of the early twentieth century, essentially answered the first question. He realised that ozone was both formed and destroyed by the action of sunlight, specifically UV radiation, on atmospheric oxygen. He calculated that this action would reduce and finally stop at a point approximately 15 km above sea level, because the reactions which had produced the ozone higher up had absorbed the UV radiation in the process. No activation energy to produce any more ozone. That explained the lower limit of ozone. The upper limit was explained by the lack of oxygen in the upper stratosphere to produce a stable layer – for production to exceed destruction. This was interesting confirmation of observations made earlier by the meteorologist and balloonist Léon-Phillippe Teisserenc de Bort, who noted that, contrary to his expectations, the air temperature didn’t fall gradually with altitude but reached a point of stabilisation where the air even seemed to become warmer. He named this upper layer of air the stratosphere, and the cooler more turbulent layer below he called the troposphere. It’s now known that this upper-air warming is caused by the absorption of UV radiation by ozone.
Our picture of ozone still had some holes in it, however, as it seemed there was a lot less of it around than the calculations of Chapman suggested. To quote from Beerling’s book:
… there had to be some as-yet unappreciated means by which ozone was being destroyed. The fundamental leap required to solve the problem was taken comparatively recently, in 1970, by a then young scientist called Paul Crutzen. Crutzen showed that, remarkably, the oxides of nitrogen, produced by soil microbes, catalysed the destruction of ozone many kilometres up in the stratosphere. Few people appreciate the marvellous fact that the cycling of nitrogen by the biosphere exerts an influence on the global ozone layer: life on Earth reaches out to the chemistry of the stratosphere.
Now to explain why the hole in the ozone shield occurred above the Antarctic. My understanding and explanation starts with reading Beerling and ends with this post from the USA’s National Oceanic and Atmospheric Administration’s Earth System Research Laboratory (NOAA/ESRL).
The ozone hole over Antarctica varies in size, and is largest in the months of winter and early spring. During these months, due to the large and mountainous land mass there, average minimum temperatures can reach as low as −90°C, which is on average 10°C lower than Arctic winter minimums (Arctic temperatures are generally more variable than in the Antarctic). When winter minimums fall below around −78°C at the poles, polar stratospheric clouds are formed, and this happens far more often in the Antarctic – for about five months in the year. Chemical reactions between halogen gases and these clouds produce the highly reactive gases chlorine monoxide (ClO) and bromine monoxide (BrO), which are destructive to ozone.
Most ozone is produced in the tropical stratosphere, in reactions driven by sunlight, but a slow movement of stratospheric air, known as the Brewer-Dobson circulation, transports it over time to the poles, so that ozone ends up being more sparse in the tropics. Interestingly, although most ozone-depleting substances – mainly halogen gases – are produced in the more humanly-populated northern hemisphere, complex tropospheric convection patterns distribute the gases more or less evenly throughout the lower atmosphere. Once in the stratosphere and distributed to the poles, the air carrying the halogen-gas products becomes isolated due to strong circumpolar winds, which are at their height during winter and early spring. This isolation preserves ozone depletion reactions for many weeks or months. The polar vortex at the Antarctic, being stronger than in the Arctic, is more effective in reducing the flow of ozone from tropical regions.
So – I’ve looked here briefly at what ozone is, where it is, and how it’s produced and destroyed, but I haven’t really touched on its importance for protecting life here on Earth. So that, and whether its depletion may have had catastrophic consequences 250 million years ago, will be the focus of my next post.
References
The Emerald Planet, by David Beerling, Oxford Landmark Science, 2009