Executive summary
Climate leaves an imprint on the planet in the chemical and physical structure of its oceans, life and land. In much the same way that archaeologists reveal past cultures by looking at artefacts, or detectives reconstruct a crime by piecing together evidence found at the scene, scientists gather evidence stored in the environment to reconstruct the history of Earth's climate over hundreds of thousands—and in some cases millions of years. When combined with observations of Earth's modern climate, evidence from the past can help us understand our present climate and predict what future climates might be like.
In Australia, high quality instrumental climate records only extend back to the late 19th century, providing just a brief snapshot of our climate's natural state and its variability. To understand the nature of our present climate and, in turn, predict our future climate we need data that go back far beyond the instrumental record. This is where palaeo-science comes in.
Palaeo-science provides the means to extend climate records back tens to thousands of years. Palaeo (meaning "ancient") records include direct and indirect (proxy) evidence of past atmospheric, terrestrial and marine conditions. The records are derived directly from the environment itself, rather than from historical documents and instrumental measurements. This evidence is wide ranging, including landscape features (such as ancient lake shorelines), and biological, chemical and isotopic material stored in sediments, ice sheets, tree rings, cave deposits and corals. Palaeo-records provide a powerful tool for reconstructing not only past climates, but also the drivers of climate change (including atmospheric concentrations of greenhouse gases), and the impacts that climate change has had on the environment.
We now have the geographic coverage and temporal resolution from palaeo-records to identify and understand cycles of climate variation and change across the Australasian region that are not evident in the instrumental records. This presents an opportunity to test and improve not only our understanding of climate change and variability in Australia, but also the processes driving climate change. This knowledge in turn can be used to test the ability of models to simulate climate, improving that ability of scientists to predict future climatic conditions. Palaeo-records provide the length of records necessary for testing climate models that instrumental records are simply too short to provide.
Importantly, palaeo-records provide us with the means to understand the degree to which current climate change is due to natural cycles and to human influences. Critical to this has been the measurement of greenhouse gases trapped in air bubbles in ice sheets (especially from Antarctica and Greenland). This direct evidence of atmospheric composition (a key driver in climate change) has allowed scientists to determine the variation in atmospheric greenhouse gases over the last 700 000 years, demonstrating clearly that the current concentrations are not only well above natural levels but that they are also accumulating at faster rates. Similarly, palaeo-records have been used to identify the roles that aerosol concentrations, solar irradiance and land cover change have had in climate forcing, both pre and post-industrial times (~1750 AD).
The information provided by palaeo-research is invaluable in helping explain how and why our climate has changed in the past and, ultimately, in helping us to assess and plan for climate change in the future. Surrounded by oceans, Australia's location in the Southern Hemisphere puts us in a unique position to contribute to the global understanding of climate change. There has recently been a push to bring together the growing number of palaeo-records to carry out cross-regional, national scale analyses to fill important geographical and chronological gaps in the climate record. This would allow the production of an Australian data set to rival that of the Northern Hemisphere, providing valuable information of past climate variation in the Australian region.
This overview is an introduction to the value of palaeo-science in the understanding of climate change in Australia. It is based on a technical report prepared for the Department of Climate Change by CSIRO in association with collaborators from other scientific institutions. The technical report should be referred to for a comprehensive analysis of the potential of palaeo-science to contribute to understanding climate change in Australia.