Atmospheric pressure

Studying the make-up of the air we breathe

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EVERY LIFE HAS those moments: arresting at the time, they also come to resonate as deeply formative given one’s later trajectory. I experienced such a moment within a week of my ninth birthday. In 1986 I was sitting in my fourth-grade classroom in rural Victoria writing a response to BTN – the ABC kids’ news show still running today, of which my own near-nine-year-old daughter is now a devotee. And I suddenly understood, in a very visceral (and frightened) way, how the entire world and all the life supported by it are intrinsically connected by the atmosphere.

A decade later, I heard Billy Bragg’s song ‘Help Save the Youth of America’ for the first time. Its reference to the Chernobyl disaster’s reminder of the smallness of the world instantly transported my nineteen-year-old self back to the kid I had been when it happened in 1986. I once again understood in the pit of my stomach how the atmosphere, the very air we breathe, binds us all together, for better or for worse. But this time, I also had an inkling of how humanity, politics, science and the natural world intersect. Nearly a quarter of a century later, this nexus continues to occupy me, the Earth’s atmosphere at its heart.

I am enormously privileged to have been entrusted with the responsibility for co-leading one of the core science programs (Greenhouse Gases and Ozone Depleting Substances) at the Cape Grim Baseline Air Pollution Station. Located on the remote, beautiful and blusterous north-west tip of Tasmania, overlooking the expanse of the Southern Ocean, Cape Grim is a cornerstone observatory in the World Meteorological Organisation (WMO) Global Atmosphere Watch Programme. It stands shoulder-to-shoulder with its more famous older sibling, Mauna Loa (Hawaii), to provide the foundational measurement records for the Southern Hemisphere that have tracked rising greenhouse gas levels and other changes in atmospheric composition influencing the climate of our planet. Often lauded as ‘the cleanest air in the world’, the composition of the air that arrives at Cape Grim from across the vast Southern Ocean is called the baseline signal. Like the resting heart rate of the planet, it has been rising as humans have added increasing stressors to the Earth system.

One of the key features of the Cape Grim Science Program is that it is just that: a science program. From the outset, the program benefitted from having strong institutional support from both the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Bureau of Meteorology (BOM), and a multi-decadal outlook, but it has also thrived because at its inception it was seen (and continues to be seen) principally as a science research program. No mere monitoring station, the program would deliver excellence in precision observations and the lead scientists would involve themselves in using data to answer important questions. There has always been an imperative to maintain quality, consistency and continuity of data records, and to expand and improve the measurement program to ensure that the next generation of questions about how our planet is functioning can be answered.

Cape Grim’s name has been an apt moniker, and a gift to headline writers in recent years. ‘Grim warning’ shouted the front page of The Sydney Morning Herald on 11 May 2016, as baseline carbon dioxide climbed inexorably towards 400 parts per million. But the name, which underscores its role as a foreboding sentinel of global atmospheric and climate change, is neither a sign of prescience nor a piece of propaganda perpetrated by the so-called ‘climate-change mafia’, to which some like to presume that climate scientists belong.

Nor does it refer to the horrific massacre of approximately thirty Indigenous locals – who called their place Kennaook – by Van Diemen’s Land Company staff on 10 February 1828. Many local landscape features have been named as cruel markers of this particular tragedy in the broader Tasmanian genocide – but not this one.

In fact, Cape Grim was named by Matthew Flinders in 1798 as he circumnavigated Van Diemen’s Land to prove it was an island, separate from the mainland. ‘The north-west cape of Van Diemen’s Land, or island, as it might now be termed, is a steep, black head, which, from its appearance, I call Cape Grim.’[i] That bleak name spoke to a moment of triumph for Flinders, having rounded the northern coastline and satisfied himself that his hypothesis was correct.


IT WOULD BE very easy to get the impression that the idea of human-driven climate change dates back barely any further than the late twentieth century, only becoming a settled question – and a compelling issue demanding action – in the twenty-first century. It might be even easier for an Australian to believe that there has never been broad political consensus on approaching the issue of anthropogenic climate change. The history of climate science and the Cape Grim Baseline Air Pollution Station tells a different story.

It was 1824 when Joseph Fourier proposed that the Earth’s atmosphere was modulating the planet’s temperature. The atmosphere was keeping the planet warmer than it would otherwise have been because, while transparent to visible light, it is able to absorb the infrared radiation emitted by the Earth’s surface in response to the absorption of that visible light. This is the greenhouse effect – carefully articulated almost 200 years ago.

Thirty-five years later, in 1859, John Tyndall empirically investigated the infrared absorption spectra of water vapour and carbon dioxide, confirming that these trace gases strongly absorb infrared radiation. By 1896 Svante Arrhenius was using Tyndall’s work (and others’) to calculate the size of the greenhouse effect if atmospheric carbon dioxidewas halved (cooling) or doubled (warming). The motivation for much of this science was to understand past climatic changes evident in the geological record, but Arrhenius also anticipated that human combustion of coal would eventually result in warming.

Through the first half of the twentieth century, climate science was a genuinely contested arena largely concerned with understanding past changes over geological timescales. Many novel theories were expounded, but new observations (often made with imprecise measurement tools) confounded clear progress in scientific understanding. A healthy scepticism pervaded the discipline. Nevertheless, by the mid-1950s, new lines of observational evidence coupled with improvements in technology were starting to shore up the evidence for rising atmospheric carbon dioxide and its role in warming the climate.

In preparation for the International Geophysical Year (1957–58), Charles David Keeling of the Scripps Institution of Oceanography set up measurements of atmospheric carbon dioxide at Mauna Loa in 1956  – and, subsequently, at the South Pole as well. Within a few short years Keeling had measured significant seasonal cycles in carbon dioxide driven by biological photosynthesis and respiration, and an underlying growth attributable to the combustion of fossil fuels. The century-old question of whether it was possible for anthropogenic activities to alter the composition of the background atmosphere had been clearly answered. They could and they were.

HOWEVER, THERE WERE other things to think about in the air. During the 1960s, there came an increasing awareness of the role of atmospheric aerosol and reactive trace gases as a source of local and regional air pollution. In cities, smog (well understood to be caused by human activities) was a growing problem for the health of citizens. As the decade drew to a close, scientific interest also turned to the role of aerosols in the background atmosphere: the cooling effect of an increasing amount of anthropogenic aerosols was masking (and, some hypothesised, might eventually overwhelm) the warming from rising carbon dioxide.

In 1969, the WMO recommended the establishment of an international Background Air Pollution Monitoring Network aimed at tracking changes in atmospheric composition that might affect climate. The time was ripe for the establishment of an Australian Baseline station.

In 1971, CHB Priestley, the CSIRO’s chief in the Division of Meteorological Physics, and WJ Gibbs, BOM director, began jointly to advocate at the highest levels for long-term and systematic observations of the background atmosphere in the Australian region. They drew on CSIRO work researching atmospheric aerosol, tropospheric (surface) ozone and nitrogen oxides. Priestley also encouraged young scientists to spread their wings (literally) in a program of aircraft-bornecarbon dioxide measurements to engage the CSIRO more closely in studying the link between atmospheric composition change and climate.

The inaugural United Nations Conference on the Human Environment (UNCHE) was held in June 1972, a pivotal event in securing an Australian Baseline station. Ahead of that meeting, experts from fourteen nations met to assess the human impact on regional and global climate. Their report concluded that ‘without additional research and monitoring programs the scientific community will not be able to provide firm answers which society may need if large scale and possibly irreversible, inadvertent modification of climate is to be avoided’.[ii]

When Liberal Prime Minister William McMahon announced his extensive and high-level delegation to the UNCHE in Stockholm, he noted that Australia ‘had been one of the first countries to support the Swedish initiative’ and that the conference would ‘consider recommendations…including a global monitoring system’. The Australian Government, he said, ‘believed the conference to be of the greatest importance’, while the ‘problems of managing the environment were among the most complex to confront mankind’. In this way, he said, the UNCHE Conference would be ‘a first important step in a long and challenging process’.[iii]

Half a century later, it’s clear exactly how long and challenging this process remains.

Peter Howson, then Minister for the Environment, Aborigines and the Arts, acknowledged that the conference had concluded with the aspiration to establish ten baseline stations across the globe, and the Australian Government was committed to at least one being in Australia. This commitment was surely necessitated partly by our geography – any global monitoring system would be sadly lacking if there were no data from this part of the world. But I suspect it was also borne of pride, and of concern to uphold our international standing; it was clear that there was a critical issue for humanity to tackle and that this would require co-operation and leadership. The Australia of that era was willing and eager to take up the mantle.

With government support assured, in late 1972 the groundwork to locate a suitable site began in earnest. Many of the key players had already articulated a rigorous set of criteria for choosing the location. Chief among these was the necessity of sampling marine air masses, free from local terrestrial and human influences for a significant proportion of the time. After initially casting a very wide net (from Lord Howe Island to Antarctica), the search had narrowed to a handful of Tasmanian sites by 1975, including Honey Smith Hill, near the South East Cape. But there were concerns about access logistics at Honey Smith Hill, and in October 1975 Lewis Wainwright of the Department of Science – newly appointed to the role of officer in charge, baseline air pollution monitoring – proposed a piece of Commonwealth land on the north-west coast as a temporary alternative to get measurements underway. That site was Cape Grim.

On 1 April 1976 at 10 am AEST, in an ex-NASA caravan donated to the cause, atmospheric carbon dioxide measurements commenced at Cape Grim. The first reading was 330.5 parts per million.

Cape Grim had not initially been on the site shortlist because it received a lower proportion of baseline air masses than some possible sites in the Tasmanian southern highlands. But as time passed, the scientific value of northerly winds – bringing the imprint of the sources and sinks of trace gases from the southern part of continental Australia, particularly Melbourne – has become increasingly clear. After carbon dioxide, methane and nitrous oxide – both of which have significant agricultural sources – have contributed the most to trapping heat in the Earth system. Cape Grim data have been used to assess south-eastern Australian fluxes of these trace gases. And then there are the synthetic greenhouse gases. Used in industrial processes, refrigeration and air conditioning, cities are hot spots for emissions of these gases. Measurements of air that reaches Cape Grim via Melbourne now routinely inform Australia’s reporting of our emissions of these gases to the United Nations Framework Convention on Climate Change. Serendipitously, Australia had sited its baseline station in precisely the right location to illuminate urban- and regional-scale trace gas emissions, while also contributing to an understanding of the global carbon cycle.

After April 1976, additional measurements of ozone, halocarbons, oxides of nitrogen, particles, precipitation chemistry, solar radiation, meteorological parameters and radon were added in short order. As this range of measurements continued to expand, Cape Grim became one of the most comprehensive atmospheric observatories in the world, offering a deep understanding of atmospheric composition. In the ever-changing combinations of its constituents, we can discern not only long-term change, but also the physical and chemical processes at play on shorter timescales and something of the recent journey the air has taken to reach the station.

While much of the conversation around climate change refers to carbon dioxide, critical non-carbon dioxide greenhouse gases also need to be monitored. The most notorious of these, perhaps, are the chlorofluorocarbons (CFCs), which have been under examination by CSIRO scientists, including Paul Fraser, since 1974 and the publication of a paper[iv] suggesting CFC emissions were a potential threat to stratospheric ozone. Though Fraser himself labelled this foray naive, with hindsight it appears prescient. Within a year, the risks posed by CFCs had widened to include climate change as well as stratospheric ozone depletion. There were no commercially available instruments to make these measurements, prompting Fraser to write directly to James Lovelock (author of the first global survey of atmospheric CFC-11 in 1973, and later of the Gaia theory). Lovelock hand-delivered one of his own purpose-built instruments in a suitcase to the CSIRO laboratories in Aspendale in suburban Melbourne during a family visit to Australia. The arrival of this bespoke instrument enabled Cape Grim’s involvement in several critical and long-running international collaborations around atmospheric gases,[v] key to identifying illegal production of CFC-11 in eastern China in 2019, in contravention of the Montreal Protocol. It also resulted in the genesis of one of the great treasures of atmospheric composition science.

In order to improve the performance of Lovelock’s instrument, Fraser established an ambient air working standard – a cylinder of perfectly ordinary whole air to be measured regularly, with a CFC-11 concentration well matched to the cleanest air samples being analysed. To implement this almost banal analytical chemists’ trick, he repurposed a World War II oxygen cylinder filled at Cape Grim on 26 April 1978. But the atmospheric growth rate of CFC-11 was so rapid that ambient concentrations of the gas had far outstripped the concentration in the original tank well before the supply of working-standard gas was exhausted, reducing its efficacy as a reference point. A new tank had to be filled to maintain instrument performance. Faced with a mounting collection of half-full cylinders, Fraser made the call to keep them – just in case a use for them was found. Another miraculous piece of prescience: eventually, regularly adding cylinders to the Cape Grim Air Archive became core business and a critical record of change.

As governments worked swiftly and co-operatively to protect the ozone layer via the 1987 Montreal Protocol, industry ramped up research to develop non-ozone depleting replacements for the culprit chemicals. Further generations of research yielded more novel industrial compounds that would be ozone-safe and would also be less potent as greenhouse gases. As a consequence of this, new synthetic trace gases began to accumulate in the background atmosphere before we had the technology to measure them at such tiny abundances. Having created and curated a library of baseline atmospheric samples throughout this period, it has been possible (once technological advances have allowed) to reconstruct the atmospheric histories of scores of trace gases and closely track the success of the Montreal Protocol – which, initially inadvertently, has also been the single most effective international treaty for limiting anthropogenic climate change to date. Thanks to bans on production and use of the CFCs, the stratospheric ozone layer is now on its way to recovery – and we have also avoided significant climate forcing, given the global warming potential of these chemicals. Moreover, while HCFCs – the first generation of CFC replacements – were much less effective ozone depleters, they were certainly potent greenhouse gases in their own right, as were their successors, the HFCs. Through the protocol, phase-out plans for all these gases have delineated a clear roadmap away from reliance on them. Through the history stored in the Air Archive, we can witness the effectiveness of the protocol, not only for the ozone layer, but also for the climate. This is astonishing, uplifting – and cause for hope on days when hope is sorely needed.


JUST AS CAPE Grim data have been used to track the success of the Montreal Protocol and identify breaches of it, other Cape Grim measurements illuminate the transport and accumulation of toxins in the environment. Mercury is another unpleaseant side-effect of coal combustion and its potential impacts are addressed by the Minamata Convention on Mercury. Substances like dichloro-diphenyl-trichloroethane (DDT) (first made notorious by Rachel Carson’s Silent Spring) are now controlled by the Stockholm Convention on Persistent Organic Pollutants (POPs). Mercury and POPs are semi-volatile chemical species that can be transported long distances through the air, but eventually come to rest on soils or in water where they enter the food chain, bioaccumulating in species as one gobbles another, with notable deleterious effects on apex predators (including humans). Mercury is a neurotoxin. DDT is renowned for disrupting reproduction in birds by causing severe eggshell thinning; all the POPs are nasty.

Anthropogenic aerosol and photochemical smog have also now been ameliorated in many of the regions where they were problematic during the 1960s (so these components are clearly not going to save us from roasting ourselves). Nevertheless, reactive gases and particles do continue to play an important, but less well understood, role in mediating climate. Particularly in the pristine air above the Southern Ocean, the role of natural aerosol in climate feedbacks remains an open question. This colossal portion of the globe is grossly under-sampled. In this context, Cape Grim science devoted to quantifying and understanding the processes of production of climatically important aerosols is vital to understanding their role in global climate overall.

At the same time, carbon dioxide emissions continue to rise, driving climate change and bringing myriad implications for air quality. In Australia, more frequent and extreme fire-weather days will continue to throw up episodes like the 2019–20 Australian fires, when almost all of the eastern seaboard (and most of the country’s population) was subjected to extraordinarily poor air quality, as cities were shrouded in bushfire smoke. As the fires raged southward, first Brisbane, then Sydney, Canberra and Melbourne were cast into protracted palls the like of which had never been experienced. In the ACT, concentrations of PM2.5 (the most insidious fine particles associated with poor air quality and health impacts) exceeded the national standard by a factor of almost forty at their peak, and between the start of November and the end of February, Canberrans were subjected to fifty-three days in which the daily average PM2.5 concentration exceeded the national standard. Even at Cape Grim, which boasts the ‘cleanest air in the world’, January 2020 was marked by days of haze.

It’s early December 2020 as I write this, a year on from last year’s horror summer. While the equilibrium pre-industrial atmospheric carbon dioxide concentration of 278 ppm had already risen to 330.5 ppm when measurements began at Cape Grim in 1976, this has hurtled upward to reach 410.8 ppm in the month just gone. In the past 800,000 years, the most rapid natural changes in atmospheric carbon dioxide occurred at a rate of around ten ppm per century. We added the latest ten ppm to the atmosphere in just four years. Fossil fuel carbon dioxide emissions reductions resulting from the widespread lockdowns imposed by many jurisdictions this year to contain the spread of COVID-19 have done little to abate rising atmospheric carbon dioxide. A La Niña summer will likely save us from a repeat of last year’s fire season – though as I write, the first fires have already arrived, and there will certainly be more. La Niña, bringing cooler, wetter conditions, might also allow the terrestrial biosphere to sequester a little more carbon dioxide than it was able to manage last year. But atmospheric carbon dioxide will keep rising, because we continue to emit it at a ferocious pace. Levels of methane, nitrous oxide and many of those synthetic greenhouse gases will also continue to rise.

The intrinsically long-term nature of the Cape Grim endeavour and its critical role in helping inform humanity of the changes it has wrought – in perpetual expectation of aiding wise choices for the road ahead – have tended to keep those involved engaged. So, although I am (more or less) of Cape Grim vintage, I have had the benefit of working alongside many of Cape Grim’s foundational lead scientists. This piece, showing my bias, focuses heavily on those areas of the Cape Grim program that align with my expertise, virtually ignoring other important measurement programs, including those for reactive gases, radon and radiation. But it is the sum of these parts, and the strength of our international collaborations, that have allowed the Cape Grim Science Program to be as holistic and scientifically robust as it is, contributing the best peer-reviewed atmospheric science to the world. Cape Grim is an entity of which Australians should be proud, and an institution that is needed more than ever as we enter the final years of the initial fifty-year vision.

Others can speak with more authority on the impacts of climate change on the terrestrial and marine biosphere; on the availability of water; on human lives on the land, and in cities – particularly in terms of the immediate impacts of severe and compound weather events, including fire weather and the more chronic problems of heat stress and air quality. But I can speak to the imperative to maintain an atmospheric vigil – to keep watch, to chart our trajectory and provide the data needed to validate and refine climate models so that we are best prepared to act. So that we can see when our collective actions are effective, and when they are not. The changes evident in Cape Grim’s forty-five-year baseline record tell the story of humanity’s profound and accelerating alteration of our planet. It is my hope that in the coming forty-five years, the Cape Grim baseline record will tell the story of humanity’s profound and rapid transition to a decarbonised economy, allowing stabilisation of our climate and preservation of as much of our natural world as is salvageable.

As a child, my father used to sing me a song called ‘The Drover’s Dream’. My favourite lines talked about frogs emerging from a swamp where the atmosphere was damp. The frogs produced ‘violin, banjo and bones’ from their swags as they bounded in and sat down together.

It was the word ‘atmosphere’ that intrigued me. Its dual meanings seemed to sit in slight tension in that stanza. The swamp’s air was damp, but those anthropomorphised amphibians were in a festive spirit, whipping out their instruments for a singalong. It now reminds me of Flinders’ mood as he bestowed a new name on Cape Grim. Perhaps my own relationship with Cape Grim holds the very same tension. The responsibility for carrying on this scientific legacy – and the prospect of human society failing to take the action necessary to avert the worst outcomes – often weigh heavily on me. And yet it is impossible not to be inspired by the visionary work of those who came before me, by my extraordinary colleagues and by the very beauty of the place itself.


[i]Terra Australis Matthew Flinders’ Great Adventures in the Circumnavigation of Australia, Edited and Introduced by Tim Flannery, Text Publishing (2000). p. 26.

[ii]Inadvertent Climate Modification: Report of the Study of Man’s Impact on Climate, The Colonial Press, USA, 308 pp., 1971.

[iii]PM Press Statement No. 49, 14 May, 1972. The document can be found at:

[iv]Molina, M. J. and F. S. Rowland, Stratospheric sink for chlorofluoromethanes: chlorine atom‐catalysed destruction of ozone, Nature, 249:5460, 810‐812, doi:10.1038/249810a0, 1974.

[v]Subsequent investigations have revealed the cylinders to have had an even earlier incarnation as ‘beverage’ containers (i.e., beer kegs) prior to World War II.

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About the author

Zoë Loh

Zoë Loh is a senior research scientist at CSIRO Oceans and Atmosphere, working in the Climate Science Centre. She leads the team responsible for...

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