Analysis of long-term ClimAte Change In Australia (ACACIA)

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Summary The aim of this project is to investigate the complex interactions between climate, vegetation changes, natural wildfires and human activities, in particular, deliberate fire-setting, over the past 70,000 years in Australia. This period encompasses the initial human colonisation (ca 55,000-45,000 years ago) and subsequent human dispersal across the continent. This colonization is set against the background of large-scale changes in regional climates and environmental conditions, specifically changes in the Australian monsoon which resulted in a significant expansion of the extent of monsoon-fed inland lakes and moisture-demanding vegetation in the mid-continent between ca 65,000 and 45,000 years ago and the subsequent aridification of the continent. Known changes in the external factors affecting regional climates, in particular changes in insolation, atmospheric composition and changes in the extent of polar ice sheets, during the past 70,000 years would have had a significant impact on the Australian monsoon. These changes in climate would in turn have led to changes in the vegetation cover -- changes that in turn influence water- and energy-exchange between the land and the atmosphere, and thus produce feedbacks on the climate system. However, the deliberate or accidental setting of fire by human colonists also affects the vegetation cover and it has been claimed that such activities are also implicated in the Late Quaternary aridification of Australia and the development of fire-adapted vegetation there. We will investigate the relative importance of changes in externally-forced climate changes and human activities in the history of Australian climates and vegetation through a series of experiments using a fast ocean-atmosphere general circulation model. In the first set of experiments, we will examine the response of Australian regional climates to changes in external climate forcing at times in the past 70,000 years corresponding to times when the differences in summer insolation from today were at a maximum or minimum. We will use a coupled vegetation-fire model to examine the effect of the simulated changes in climate on natural vegetation and wildfires. Finally, we will develop plausible scenarios of the extent of human-set fires, based on archaeological evidence for population distribution, density and cultural practices, and use the coupled vegetation-fire model to investigate the impact of human activities on the vegetation and the likely impact of human-induced changes on the climate. Exploring the relative importance of externally-forced climate changes and human activities on regional climate changes and the development of the fire-adapted vegetation characteristic of Australia today will provide a basis for predicting how these relationships will change in the future, and will therefore contribute to the development of improved risk analysis and environmental management tools for a fire-prone continent.