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

这个合作项目的目的是解决一个关于全新世气候的基本而尚未解决的问题，即：人类何时担任全球气候系统的“驾驶座”？它是像传统上认为的那样与工业时代的到来同时发生的，还是在几千年前与农业的出现一起发生的？科学界仍然存在分歧，早期农业活动释放的碳排放量是否足以解释全新世晚期大气温室气体（GHG）浓度前所未有的上升，而这些气候驱动因素在最近的前几次间冰期期间有所下降。这项研究将通过确定过去6年人类对全球气候影响的“指纹”来检验“早期人为假说”，该假说认为，人类活动导致的全球气候变化是由全新世中期的农业引起的，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”气候演变。如果没有人类的土地清理和温室气体的过度排放， 为了实现这一目标，将使用社区地球系统模型（CESM）进行一对6,000年的瞬态模拟。 在一项实验中，CESM将由轨道参数、温室气体浓度和区域土地清理的历史变化驱动，而后两种强迫在对应的实验中将根据二氧化碳和甲烷的假设下降以及与“自然”相容的相关全球植被格局而不同。更广泛的影响涉及在科学上理解人类对全球气候的影响方面发生独特和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.