The Earth's climate is changing, and the driving forces are changes occurring in the composition of the planet's atmosphere.
At Tasmania's Kennaook/Cape Grim site, the Bureau of Meteorology operates a scientific observatory to measure the composition of some of the world's cleanest air.
The station is on Tasmania's west coast, near the north-west tip — the location chosen because, when conditions are right, the air at Kennaook/Cape Grim has been transported from the vast Southern Ocean, by way of the westerly winds frequently encountered.
This air is representative of the "global" atmosphere, unaffected by local pollution.
The science program at Kennaook/Cape Grim is a collaboration between the bureau and CSIRO, with contributions from the Australian Nuclear Science and Technology Organisation (ANSTO), the University of Wollongong and other groups from around the world.
The science program manages a team that chronicles the changing composition of the Earth's atmosphere to inform Australia and the world about the basic drivers of the changing climate.
From this air, the science team measures:
- Greenhouse gases that drive climate change
- Substances that cause the hole in the ozone layer (stratospheric ozone depletion)
- Other features of the atmosphere that affect climate, directly or indirectly.
Scientists from around the world use data to understand the life cycle and impacts of various parts of the atmosphere, and how their influence changes over time.
The data also enables scientists to calculate emissions of harmful substances nationally and globally.
Global monitoring of atmospheric composition
Kennaook/Cape Grim Baseline Air Pollution Station and the related science program are guided by the World Meteorological Organization's Global Atmosphere Watch program.
Elements of atmospheric composition are measured at several sites around the world.
Few of these, and none in the southern hemisphere, do this as comprehensively as at Kennaook/Cape Grim.
Data from this station is stored in the world data centres coordinated by the Global Atmosphere Watch program.
Measuring greenhouse gases
Greenhouse gas measurements began at this station in 1976. It started with carbon dioxide and various halo carbons, which are potent synthetic greenhouse gases.
Carbon dioxide at that time was recorded at 330 parts per million (ppm). Nearly half a century later, it has increased by about 25 per cent.
Work from the station now captures all of the major greenhouse gases, including:
- Carbon dioxide, CO2
- Methane, CH4
- Nitrous oxide, N20
It also includes synthetic gases such as:
- Chlorofluorocarbons (CFCs)
- Hydrochlorofluorocarbons (HCFCs)
- Hydrofluorocarbons (HFCs)
- Perfluorocarbons (PFCs)
- Sulphur hexafluoride (SF6)
Monitoring ozone-depleting substances
Ozone in Earth's stratosphere protects our planet from some of the Sun's harshest radiation.
Ozone-depleting substances are chemicals that destroy ozone in the stratosphere. These gases are responsible for the hole in the ozone layer. Many of these are also potent greenhouse gases.
Concerns about the impact of these chemicals led to the Vienna Convention for the Protection of the Ozone Layer in 1985.
This was followed by the Montreal Protocol on Substances that Deplete Ozone in 1987.
The Montreal Protocol sought to curb production and called for ongoing monitoring of these chemicals in the atmosphere. Measurements from Kennaook/Cape Grim allow Australia to meet some of these monitoring requirements.
The science team at the station routinely measures all the significant ozone-depleting substances.
This is possible through a collaboration with the international Advanced Global Atmospheric Gases Experimental (AGAGE) network.
Other measurements at Kennaook/Cape Grim
Measurements of greenhouse gases and ozone-depleting substances are an important part of the work at Kennaook/Cape Grim, but there is much more.
The composition of the Earth's atmosphere is changing in complex and subtle ways.
These changes influence how the atmosphere and climate respond. For example:
- Atmospheric particles can influence how light from the sun passes through the atmosphere. Particles are also critical in cloud formation
- Reactive gases such as nitric oxides and ozone influence the chemistry of the atmosphere. They are also involved in particle formation
- Radon measurements tell if the air being measured has recently been over land, so works as a tracer
The science team takes detailed and precise measurements of these and more. This enables chronicling of the influence of all these factors and to understand changes over time.
The bureau and CSIRO, along with contributions from the Australian Nuclear Science and Technology Organisation (ANSTO) and the University of Wollongong, have been chronicling the changing composition of the global atmosphere, through their work at Kennaook/Cape Grim, since 1976.
The work continues.
More information can be found at the CSIRO's Cape Grim Data website.
Sam Cleland is the Officer in Charge at the Kennaook/Cape Grim Baseline Air Pollution Station
