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

这个项目的目的是调查过去7万年澳大利亚气候、植被变化、自然野火和人类活动之间复杂的相互作用，特别是故意放火。这一时期包括最初的人类殖民（大约55000 - 45000年前）和随后的人类遍布整个大陆。这种殖民是在区域气候和环境条件发生大规模变化的背景下进行的，特别是澳大利亚季风的变化，导致大约6.5万到4.5万年前，季风滋养的内陆湖泊和需要水分的植被的范围显著扩大，以及随后大陆的干旱化。在过去7万年中，已知的影响区域气候的外部因素的变化，特别是日照、大气成分和极地冰盖范围的变化，将对澳大利亚季风产生重大影响。这些气候变化反过来又会导致植被覆盖的变化——这些变化反过来又影响陆地和大气之间的水和能量交换，从而对气候系统产生反馈。然而，人类殖民者故意或意外纵火也会影响植被覆盖，有人声称这种活动也与澳大利亚晚第四纪干旱化和适应火灾的植被的发展有关。我们将通过使用快速海洋-大气环流模式的一系列实验，调查外部强迫气候变化和人类活动变化在澳大利亚气候和植被历史中的相对重要性。在第一组实验中，我们将研究澳大利亚区域气候在过去7万年中对外部气候强迫变化的响应，这些变化对应于夏季日照与今天的差异达到最大值或最小值的时间。我们将使用植被-火灾耦合模型来研究模拟的气候变化对自然植被和野火的影响。最后，我们将基于人口分布、密度和文化习俗的考古证据，开发人类纵火程度的合理情景，并使用植被-火灾耦合模型来研究人类活动对植被的影响以及人类引起的气候变化的可能影响。探索外部强迫气候变化和人类活动对区域气候变化的相对重要性，以及今天澳大利亚适应火灾的植被特征的发展，将为预测这些关系在未来将如何变化提供基础，因此将有助于开发改进的风险分析和环境管理工具。

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.