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

Lead Research Organisation: University of Bristol
Department Name: Geographical Sciences


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.


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Description We have documented the changing climate and environments of Australia since the last glacial, and set this in the context of the wider changes experienced globally.

We have shown that fire is low in glacial periods and high in interglacial periods because it is strongly controlled by climate conditions affecting both fuel availability and fire spread.

We have shown that wildfire has become less widespread over the 20th century than in the pre-European period as a result of fire suppression.

We have shown that state-of-the-art climate models are unable to reproduce the evolution of Australian climates from glacial to interglacial.

We have developed a mechanistic and biologically-realistic fire model that reproduces modern day Australian fire regimes, and also palaeofire regimes. We have also used this model to predict the likely consequences of future changes in climate. These simulation show that, although fire will increase during the 21st century, this will not have a negative impact on the carbon budget because of the presence of fire-adapted trees.
Exploitation Route Palaeoclimate reconstructions are now being widely used for evaluation of the climate models that are used to predict the future, as part of the CMIP exercise. Our results will provide a new benchmark data set for this exercise -- there has previously been no such data set for Australia.

Our improved understanding of the controls on fire regimes provides information for the management of wildfires.

Our validated fire model has already been used to predict the likely impacts of changing climate and land-use on Australian fire regimes during the 21st century. The model is global and can be used to make similar projections for other regions of the world. The model can also be used to explore the consequences of past climate and/or land use changes, to quantify the impact of CO2 changes on fire regimes, or to explore management of fire regimes.
Sectors Agriculture, Food and Drink,Environment,Culture, Heritage, Museums and Collections

Description Our findings have been used in Australian policy briefing documents describing climate and environmental changes in the geologic past as a background to understanding ongoing impacts of climate change. Our work also is used in the WG1 report to the IPCC, 2013.
Sector Environment
Impact Types Policy & public services