On the windswept tip of north-western Tasmania, at a place long known to the Palawa people as Kennaook, sits one of the world’s most important scientific time capsules. Since 1978, the Cape Grim Air Archive (CGAA) has been collecting and preserving some of the cleanest air on Earth. Today, this “library of atmospheres” offers an unparalleled record of how our planet’s atmosphere has changed over the past five decades.
Cape Grim is no ordinary sampling site. Perched above the Southern Ocean, it lies directly in the path of the powerful “Roaring Forties” winds. These westerlies sweep across thousands of kilometers of open sea before reaching Tasmania’s cliffs, carrying with them air that has been largely untouched by human activity. That purity makes Cape Grim one of the best places in the world to monitor baseline atmospheric conditions.
Cylinders containing air samples in storage at the Atmospheric Research facility in Aspendale, Victoria. Credit: Wikimedia Commons
The first air sample was drawn on 26 April 1978, stored in a high-pressure stainless steel cylinder. Four to six times each year, new samples have been added to the collection, creating a nearly unbroken atmospheric record.
In the early years, many of the cylinders were recycled from World War II aviation oxygen tanks. These cylinders were originally used as beverage containers, before they were repurposed for storage of breathing oxygen on US military aircraft during World War II. Later, scientists switched to specially manufactured, electropolished vessels that could safely hold air at pressures up to 60 atmospheres. While the air is collected at Cape Grim, the cylinders themselves are stored at the CSIRO Marine and Atmospheric Research facility in Aspendale, Victoria.
Today, the archive contains more than 170 samples spanning almost half a century. Each cylinder is a sealed snapshot of the air as it once was.
Workers prepare repurposed beverage containers to aviation oxygen cylinders at a factory on February 1942. Credit: Shorpy
The station measures all major and minor greenhouse gases; ozone-depleting chemicals; aerosols (including black carbon or soot); reactive gases including lower-atmosphere ozone, nitrogen oxides and volatile organic compounds; radon (an indicator of changes to the land); solar radiation; the chemical composition of rainwater; mercury; persistent organic pollutants; and finally the weather.
Measurement of these greenhouse gases have shown continuous increases in concentration since the mid-to-late 1970s. However, the concentration of some ozone-depleting substances, such as CFCs and halons, have been declining confirming the success of the Montreal Protocol in phasing out many of them. The CGAA has also helped extend the timelines for newly recognized compounds. For example, HCFC-133a, only directly measured since 2014, can be traced back through the archive to 1978.
Measurements at Cape Grim have contributed significantly to global understanding of marine aerosols, including some of the first evidence that microscopic marine plants (phytoplankton) are a source of gases that play a role in cloud formation. With 70% of the Earth’s surface covered by oceans, aerosols in the marine environment play an important role in the climate system.
The CGAA have also demonstrated the impact of human activity on the atmosphere. For example, CO₂ has increased from about 330 parts per million (ppm) in 1976 to more than 400 ppm today, an average increase of 1.9 ppm per year since 1976. Since 2010 the rate has been 2.3 ppm per year. The isotopic ratios of CO₂ measured at Cape Grim have changed in a way that is consistent with fossil fuels being the source of higher concentrations.
These discoveries feed into global climate assessments, including reports from the IPCC (Intergovernmental Panel on Climate Change) and ozone assessments led by the UNEP/WMO. In fact, the Cape Grim Air Archive is widely regarded as the most extensive and valuable air archive in existence. Alongside stations at Mauna Loa in Hawaii and Alert in the Canadian Arctic, Cape Grim forms one of the three premier baseline monitoring sites in the world.
As climate concerns deepen, the archive grows more valuable with every cylinder, allowing scientists to bridge deep history and offer a clearer picture of how humans are reshaping the air we breathe.
References:
# “Cape Grim Air Archive”, CSIRO
# “Kennaook/Cape Grim Baseline Air Pollution Station”. CSIRO
# “Forty years of measuring the world's cleanest air reveals human fingerprints on the atmosphere”. CSIRO
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