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Forty years of measuring the world's cleanest air reveals human fingerprints on the atmosphere
In 2016, an isolated scientific outpost in northwest Tasmania made a historic finding. The Cape Grim Baseline Air Pollution Station measured carbon dioxide levels in the atmosphere exceeding 400 parts per million.
This wasn’t the first time the world has breached the symbolic climate change threshold – that honour was reached by the northern hemisphere in 2013 – but it was a first for the south.
Behind these recent findings is a history of Australia’s role in global scientific advancement. The Cape Grim station has now been running for 40 years and the resulting data set chronicles the major changes in our global atmosphere.
A national responseIn 1798, Matthew Flinders’ encounter with Cape Grim confirmed to Europeans that Tasmania (then Van Diemen’s Land) was separated from the mainland of Australia.
Fast forward to the early 1970s and a small group of innovative scientists were hatching a plan to take advantage of Cape Grim’s isolation and unique geographical position. The site soon became one of the world’s most significant atmospheric measurement sites, meticulously measuring and recording some of the cleanest air that can be accessed on the planet.
There were two threads to the beginnings of Cape Grim. One was the young scientists at CSIRO, keen to pioneer an emerging field of science. The second was a call from the United Nations for global governments to work together to set up a network of monitoring stations. The Australian response was championed by Bill Priestley and Bill Gibbs, the respective senior climate figureheads at CSIRO and the Bureau of Meteorology.
The scientific community decided that Cape Grim was the most appropriate site for a permanent monitoring station, thereby establishing in 1976 the Cape Grim Baseline Air Pollution Station.
The first set of instruments lived in an ex-NASA caravan. Today the station is managed by the Bureau of Meteorology and housed in a permanent building that features state-of-the-art infrastructure, including a tower fitted with important monitoring equipment. Many of the early pioneering scientists are still actively involved in this research.
The first set of air monitoring instruments lived in an ex-NASA caravan. CSIRO/Bureau of Meteorology The world’s cleanest airThe station, part of the World Meteorological Organisation’s Global Atmosphere Watch network, was sited at Cape Grim to take advantage of the “roaring forties” - the prevailing westerly winds that bring clean air from over the Southern Ocean to the station.
Air that arrives at the station from the southwest is classified as “baseline” air. Having had no recent contact with land, it represents the background atmosphere and is perhaps some of the cleanest in the world.
While we focus on this clean air, most of the instruments monitor continuously, regardless of wind direction, and can detect pollution from Melbourne and other parts of Tasmania in certain conditions.
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.
The Cape Grim Air Archive, initiated by CSIRO in 1978 and soon adopted into the operations of the station, is now the world’s most important and unique collection of background atmospheric air samples, underpinning many research papers on global and Australian emissions of greenhouse and ozone depleting gases.
The human fingerprintCape Grim data are freely available and have been widely used in all five international climate change assessments (1990-2013), all ten international ozone depletion assessments (1985-2014), in four State of the Climate Reports 2010-2016 and in lower-atmosphere ozone assessments.
Measurements at Cape Grim have 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.
Cape Grim has also demonstrated the effectiveness of action to reduce human impacts. The decline in concentrations of ozone-depleting substances measured at Cape Grim demonstrates the progress of the Montreal Protocol, an international agreement to phase out the use of these chemicals, and leading to the gradual recovery of the ozone hole.
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.
Cape Grim data are also used by the Australian government to meet international obligations. For example, the station’s greenhouse gas data have independently verified parts of Australia’s National Greenhouse Gas Inventory, which reports Australia’s annual emissions to the United Nations Framework Convention on Climate Change. Persistent organic pollutants have been reported to the Stockholm Convention on these chemicals and Cape Grim mercury data will be reported to the Minimata Convention.
Data collected from the Cape Grim Station have been used in more than 700 research papers on climate change and atmospheric pollution. By working with universities Cape Grim is a training ground for the next generation of climate scientists.
CSIRO/Bureau of MeteorologyMelita Keywood is employed by CSIRO and receives funding from the Department of the Environment and Energy, Australian Bureau of Meteorology, University of Wollongong.
Paul Fraser receives funding from MIT, NASA, Australian Bureau of Meteorology, Department of the Environment and Energy, and Refrigerant Reclaim Australia.
Paul Krummel receives funding from MIT, NASA, Australian Bureau of Meteorology, Department of the Environment and Energy, and Refrigerant Reclaim Australia.
Sam Cleland does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.
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Hurt by sea: how storm surges and sea-level rise make coastal life risky
The journal Climatic Change has published a special edition of review papers discussing major natural hazards in Australia. This article is one of a series looking at those threats.
Australia is a huge continent, but a coastal nation. About 80% of Australians live within 50km of the coast, and a sea-level rise of 1.1 metres (a high-end scenario for 2100) would put about A$63 billion (in 2008 dollars) worth of residential buildings at risk.
Anyone who lives along Sydney’s northern beaches, especially in Collaroy, saw at first hand the damage the ocean can wreak on coastal properties when the coastline was hit by a severe east coast low during a king tide in June.
There are many different factors that determine which coastal homes or suburbs are most at risk of inundation or erosion, either now or in the future. In a review published as part of a series produced by the Australian Energy and Water Exchange initiative, we investigated the causes of extreme sea levels and coastal impacts in Australia, how they have changed, and how they might change even more. While significant progress has been made over recent decades, many questions remain.
The first factor to consider is the average sea level, relative to the land elevation. This “background” sea level varies, both from year to year and season to season. Depending on where you live and what the climate is doing, background sea level can fluctuate by up to about 1m. Around Australia’s northern coastline, for example, El Niño and La Niña can cause large variations in year-to-year sea levels.
On top of this are the tides, which rise and fall predictably, and whose range varies by location and phase of the moon. Most places have two tides a day, but curiously some only have one - including Perth.
On top that again is the effect of the weather, the most notable short-term effects being storm surges and storm waves. During a surge, the storm pushes extra water onto the coast through a combination of wind pressure, wave buildup, and atmospheric pressure changes. Obviously these factors are much more localised than tides.
Extreme sea-level events, such as the one that hit Sydney in June, can arise from isolated events such as a storm surge. But more often they are due to a combination of natural phenomena that on their own may not be considered extreme. In Sydney, several factors aligned: a storm surge driven by an east coast low, an uncommon wave direction, a king tide, and a higher-than-average background sea level.
These processes already have the capacity to destroy coastal homes and infrastructure. But for the future, we also need to factor in climate change, which will raise the background sea level and may also change the frequency and intensity of storms.
Long-term trendsAverage sea levels in Australian waters have been rising at rates similar to (but just below) the global average. Since 1993, Australian tide gauges show an average rise of 2.1mm per year, whereas satellite observations reveal a global average rise of 3.4mm per year.
What really counts is extreme sea levels, and these have been rising at roughly the same rate, meaning that the rising background sea level is a fairly good guide to how extremes are increasing.
The effects of a king tide on Queensland’s Gold Coast. Bruce Miller/CSIRO, CC BYThis trend will continue in the future, although more energetic storm systems may also cause larger storm surges and hence higher rates of extreme sea levels in some places. More frequent storms are also set to make extreme sea-level events more common.
By 2100, global average sea level is projected to rise by 0.28-0.61cm, relative to the period 1986-2005, if this century’s global warming can be held to about 1℃. But if greenhouse emissions continue to increase at their current rate, the world is in line for sea-level rises of 0.52-0.98cm.
This rise will not be uniform around Australia’s coastline. The east coast is likely to experience up to 6cm more sea-level rise than the global average by 2100, because of the expected warming and strengthening of the East Australian Current.
Trends in Australia’s weather and waves are harder to predict. Satellite measurements over the past 30 years suggest that waves are getting slightly higher in the Southern Ocean, and climate models suggest that this may continue. As the tropics continue to expand with climate change, the band of westerly winds over the Southern Ocean will retreat further south and strengthen, whipping up higher waves that will travel to Australia’s southern coast as swell. On the other hand, weakening winds nearer to Australia may help to dampen down wave heights. On Australia’s eastern coast, climate models suggest fewer large wave events due to decreasing storminess in the Tasman Sea in the future.
A significant challenge we face is not having the data available to monitor the changes along our southern coastline. Australia has the longest east-west continental shelf in the world, but we have only a handful of wave buoys to measure these processes; much of the coastline is not monitored despite widespread coastal management concerns.
Our understanding of extreme sea-level change in Australia is also limited by available tide gauge coverage. Only two digital tide gauge records (in Fremantle and Fort Denison) extend back to at least the early 20th century, and records elsewhere around the coast typically span less than 50 years.
However, our investigation discovered that there is an opportunity to increase the length of available records by digitising old paper tide gauge charts. This could extend several records along our southern and tropical coastlines.
We also have major gaps in our knowledge about how our coastlines will be changed by flooding and erosion. The simple methods used to predict coastal erosion may underestimate erosion significantly, particularly in estuaries.
Given the considerable urban infrastructure located within estuaries, and the fact that they are vulnerable both to coastal storms and river floods, this is one of the many crucial questions about life on the coast that we still need to answer.
Kathleen McInnes works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.
Mark Hemer works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.
Ron Hoeke works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.