think climate. think change.
Department of Climate Change
A research brief for the Australian Greenhouse Office prepared by CSIRO in association with scientific collaborators, 2007
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In Australia, high quality instrumental climate records only extend back to the late 19th century and therefore only provide us with a brief snapshot of our climate, its mean state and its short-term variability. Palaeo-records extend our knowledge of climate back beyond the instrumental record, providing us with the means of testing and improving our understanding of the nature and impacts of climate change and variability in Australia.
There is a vast body of palaeo-records available for the Australian region (including Antarctica), ranging from continuous records of sub-decadal up to millennial scale (such as those derived from tree rings, speleothems, corals, ice cores, and lake and marine sediments) through to discontinuous records representing key periods in time (such as coastal deposits, palaeo-channels, glacial deposits and dunes). These records provide a large array of evidence of past atmospheric, terrestrial and marine environments and their varying interactions through time. There are a number of key ways in which this evidence can, in turn, be used to constrain uncertainties about climate change and its potential impacts in Australia.
Palaeo-records have been used to extend Australian records of climatic parameters (e.g. precipitation, air temperature, evaporation and sea surface temperature) back hundreds of thousands of years. Annual and sub-annual resolution records have been of particular use in extending back the climate records in southern, western and north-eastern Australia. To date, these high-resolution records only extend back hundreds to a few thousand years, restricting our ability to identify long-term climate trends and variation at an annual scale. Longer records are available, providing evidence of climatic parameters on millennial scales. However, these are generally of much coarser resolution, although there is potential for higher resolution to be obtained with additional research.
We now have the spatial and temporal coverage from these records to begin to identify and understand cycles of climate variation which are not evident in the instrumental records. Long, continuous records provide evidence of millennial scale cycles of climate change (such as 100,000 year glacial-interglacial cycles and 1,500 year Dansgaard-Oescher cycles). The latter has been observed to affect El-Niño Southern Oscillation (ENSO) cycles, with phases of ‘warm’ and ‘cool’ ENSO events. Long records also provide evidence of long-term climate change, such as the trend of increasing aridity apparent for Australia within the last 350,000 years. Higher resolution, continuous records give evidence of decadal and sub-decadal scale climate variation, such as that associated with the Indian Ocean Dipole1. In addition, by comparing records from different regions it is possible to identify spatial variation and/or synchronicity in climate cycles. This not only allows us to assess the degree to which observed regional climate variation and change across Australia can be explained by natural processes, but can also improve our understanding of the relative effects of local and global climate drivers.
Evidence for variation in greenhouse gases over the last 500,000 years has been derived from direct measurement from air enclosed in ice sheets (Antarctica, Greenland, the Arctic, and high altitude temperate and tropical glaciers), as well as proxy evidence from tree rings, corals, speleothems and plant fossils.
These records have been used to:
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).
Sound, well dated and well understood palaeo-records are playing an increasing role in climate modelling. Palaeoclimatic data can potentially provide important additional information on the behaviour of key processes in the global climate system of regional to global significance. This information is of significant value for climatic modelling. In addition, palaeo-data are necessary to both initialise past climate simulations and to validate results of past simulations. These simulations in turn are extremely valuable for testing the global climate models that are used to project future climate change. They provide the length of records necessary for testing climate models that instrumental records are simply too short to provide.
Finally, palaeo-records provide valuable insights into how climate variation and change has and could affect our terrestrial and marine environments. In particular, they allow the identification of sensitivities and vulnerabilities. This information has great potential to be used in our planning for future climate change.
