Collaborative Research: P2C2--Late Holocene Climate: Natural or Anthropogenic?

这个合作项目旨在解决关于全新世气候的一个基本但尚未解决的问题：人类何时占据了全球气候系统的“驾驶座”？它是像传统认为的那样恰逢工业时代的到来，还是发生在几千年前农业出现的时候？科学界对于早期农业活动释放的碳排放量是否足够大，是否足以解释大气温室气体(GHG)浓度在晚全新世期间前所未有地上升，而这些气候驱动因素在最近几次间冰期期间下降的问题上，仍然存在分歧。这项研究将通过识别过去6000年人类对全球气候影响的“指纹”来检验“早期人类假说”，该假说认为人类造成的全球气候变化是由农业在全新世中期启动的。该项目将利用最先进的地球系统模型来区分全新世晚期的实际气候演变和假设的“自然”轨迹，如果没有人类土地开垦和温室气体叠加，就会遵循这种轨迹。为了实现这一目标，将利用共同体地球系统模型(CESM)进行两个长达6000年的瞬变模拟。在一个实验中，CESM将由轨道参数、温室气体浓度和区域陆地清理的历史变化驱动，而后两种作用力在对应的实验中将不同，根据假设的二氧化碳和甲烷的下降以及相关的全球植被模式与“自然”气候演变相适应。更广泛的影响涉及到对人类对全球气候影响的科学理解发生独特的、潜在的变革性转变的可能性。

This collaborative project generally aims to address a fundamental and yet unresolved question about Holocene climate which is: When did humans assume the "driver's seat" of the global climate system? Did it coincide with the advent of the Industrial Era, as traditionally believed, or did it instead occur many millennia ago with the emergence of agriculture? The scientific community remains divided on whether carbon emissions released by early farming activities were large enough to explain the unprecedented rise in atmospheric greenhouse gas (GHG) concentrations during the late Holocene compared with declines in these climatic drivers during recent previous inter-glacial periods. This research will test the "Early Anthropogenic Hypothesis," which posits that anthropogenic global climate change was initiated by agriculture in the middle Holocene, by identifying the "fingerprint" of human influence on global climate during the past 6,000 years.The project will capitalize on state-of-the-art earth system models to distinguish between the actual climatic evolution of the late Holocene and the hypothesized "natural" trajectory that would have been followed in the absence of human land clearance and greenhouse-gas overprints. To achieve this goal, a pair of 6,000-year long transient simulations will be run with the Community Earth System Model (CESM). In one experiment CESM will be driven by historical variations in orbital parameters, GHG concentrations, and regional land clearance, whereas the latter two forcings will differ in the counterpart experiment according to the hypothesized declines in carbon dioxide and methane and the associated global vegetation patterns compatible with "natural" climate evolution.The Broader Impacts involve the potential for a unique and potentially transformative shift in the scientific understanding of human influence on global climate.