| Past climate change > Earlier changes | |||||||||
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| Because Australia's high quality instrumental climate records only extend back to the late 19th century, palaeo-records are used to estimate climate variability and trends before then. Palaeo-records include tree rings, ice cores, cave deposits and corals. By analysing their growth and material contained in these records we can determine a great deal about our climate. Landscape features, such as beach ridges and other sedimentary deposits can also tell us about our early climate. Palaeo-records increase our understanding of what climate variations can occur naturally, assisting in our interpretation of current climate trends. The majority of palaeo-information is from the southern, eastern and northern regions of Australia. |
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| Temperature | |||||||||
| Pollen records suggest that annual temperatures in southeast Australia between 9,000 and 5,000 years ago were slightly higher than today, as the Earth shifted into the current warm phase. | |||||||||
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| Rainfall | |||||||||
| Pollen records in eastern Australia indicate that between 9,000 and 3,500 years ago, rainfall was generally higher than present. Evidence from lakes in Victoria suggest that conditions between about 2,000 years ago to AD 1840 were wetter than present, after which the dry conditions of the recent instrumental period became established. | |||||||||
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| Extreme Events | |||||||||
| The tropical cyclone palaeo-record for Cairns and the Great Barrier Reef for events spanning the last 5,000 years shows that the historical record underestimates by an order of magnitude the frequency of the most severe tropical cyclones likely to strike the Cairns region and that the historical record of cyclones in Cairns and the east coast of Queensland coincides with a period of relative quiescence in tropical cyclone activity. | |||||||||
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| Atmospheric composition | |||||||||
| Analyses of the air trapped in bubbles in Antarctic ice cores clearly show that the present concentration of greenhouse gases in the atmosphere exceeds anything that has been experienced over at last 650,000 years. These records also indicate that concentrations of the main greenhouse gases are highly correlated with temperature over hundreds of thousands of years. | |||||||||
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| Climate trends and shifts | |||||||||
| Palaeo-records provide evidence of long-term climate trends, such as the trend of increasing aridity apparent for Australia within the last 350,000 years. Evidence from Tasmanian tree rings indicates significant shifts in the intensity of climate variability over the last 3,000 years, with a recent shift occurring around AD 1900. Evidence from Antarctic ice records have shown shifts in the circumpolar atmospheric circulation over the last 700 years which have in turn affected the variability of rainfall in Western Australia. | |||||||||
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