Holocene climate change, ecosystem response and human impacts

本研究项目主要研究冰期向间冰期过渡期间地球生态系统的演化。它的目标是了解气候系统在过去是如何变化的，以响应包括人类影响在内的各种强迫因素。我们利用化石记录重建了过去的气候和植被，开发和利用了湖泊沉积物、海洋和冰芯等过去气候和环境变化的档案。该研究项目的主要重点是绘制古气候、古植被和过去人类种群数据库的地图和统计分析，以了解北美以及更长远的全球生态系统的演变。时间尺度是过去两万年；从冰期到间冰期并进入人类世的过渡。我们将使用从湖泊沉积物、冰芯、海洋沉积物、树木年轮和其他来源收集的许多不同代用物（微化石、地球化学参数、同位素、生物标志物等）衍生的全球过去气候数据库来了解过去2万年气候是如何变化的。通过制图和统计分析，研究气候系统是缓慢变化还是突然变化，区域最高气温和最低气温何时出现，降水在时间和空间上如何变化，以及全球和区域气候在何时发生重大转变。我们将探索新的数据分析方法，如机器学习，以及多元、时间序列和空间统计等经典方法来总结和绘制这些数据。然后，我们将利用来自世界各地的花粉数据库来重建过去的植被动态。植被变化将与独立确定的气候变化相关联，以确定陆地生态系统是否对气候变化作出快速反应，或者植被变化对几个时间尺度的气候变率是否存在阈值或滞后。该提案的创新之处在于量化人类对全新世植被和气候的影响。我们使用全球考古放射性碳数据库来绘制和分析随时间变化的人口密度。这些古人口学结果被解释为与人类对环境的影响成正比，并与植被和气候变化进行统计关联，以研究(a)过去的气候变化是否影响人口数量，和/或(b)植被组成和气候与人口数量变化的关系（早期人类世假说）。我们还使用木炭数据库研究人类对自然火灾制度的影响。这些研究是在区域到大陆的尺度上进行的，总体目标是对过去气候变化如何驱动植被反应的全球分析，这反过来又有助于确定人口的变化。

This research program studies the evolution of the earth ecosystem during the transition from the glacial to interglacial period. It has as goal understanding how the climate system has changed in the past, in response to various forcing factors including human impacts. We reconstruct past climates and vegetation using the fossil record, and develop and use archives of past climate and environmental changes such as lake sediment, ocean and ice cores. The main focus of this research program is the mapping and statistical analysis of databases of paleoclimates, paleo-vegetation and past human populations to understand the ecosystem evolution of North America, and, in the longer term, globally. The time scale is the past 20,000 years; the transition from a glacial period to an interglacial and into the Anthropocene. We will use a global database of past climates, derived from many different proxies (microfossils, geochemical parameters, isotopes, biomarkers, etc,) collected from lake sediments, ice cores, ocean sediments, tree-rings and other sources to understand how the climate has changed over the past 20,000 years. Using mapping and statistical analysis, we will study if the climate system changes slowly or abruptly, when were the maximum and minimum temperatures by region, how precipitation changed in time and space and when were major transitions in global and regional climates. We will explore new data-analytic methods, such as machine learning, in addition to classical methods of multivariate, time series and spatial statistics to summarize and map these data. Then we will use pollen databases, which are available from many parts of the world, to reconstruct past vegetation dynamics. Vegetation changes will be associated with the climate changes determined independently to see if terrestrial ecosystems respond rapidly to climate changes, or if there are thresholds or lags in vegetation change to climate variability of several timescales. An innovative part of the proposal is to quantify human impacts on the vegetation and climate over the Holocene. We use a global archaeological radiocarbon database to map and analyze human population density though time. These paleodemography results are interpreted as proportional to human impact on the environment, and are statistically associated with vegetation and climate changes to study (a) did past climate changes affect human population numbers, and/or (b) are vegetation composition and climate associated with changes in human numbers (early Anthropocene hypothesis). We also study human impact on natural fire regimes using a charcoal database. These studies are done at regional to continental scale, as appropriate, and the overall goal is a global analysis of how past climate changes drove vegetation responses, which in turn helped determine human population changes.