Collaborative Research: P2C2--ICECAP (Ice Age Chemistry and Proxies) Phase 3: Investigating Fire Activity and its Implications for Climate Across Multiple Timescales

该项目旨在审查过去火灾活动的不同记录，以此作为一种手段，以增进对火灾活动随时间和气候条件变化的了解。野火对地区和全球气候变化影响很大。火灾影响到碳储存、生物地球化学循环、当地水文、陆地反照率、海洋肥力以及具有辐射重要性的气体和气溶胶的排放。例如，在雪和冰覆盖的表面沉积火黑碳(BC)会降低反照率，导致冰雪融化，反照率进一步丧失，从而导致气候变暖。尽管火灾对地球-大气系统很重要，但对过去火灾活动的了解相对较少。南极冰芯中一氧化碳(CO)和碳化碳的冰芯记录在过去150年中并没有显示出一致的趋势，而木炭记录和冰芯碳化碳的趋势有时在更长的时间尺度上是不一致的。上一次冰川时期的木炭和BC记录显示，与Dansgaard/Oeschger(D-O)事件有关的巨大变化，但这些变化对气候的影响尚不清楚。该项目的第一阶段涉及对1750年以来野火活动和气候反馈的250年模拟的严格验证。在对模型性能获得信心后，研究人员将模拟理想D-O事件选定阶段的野火活动和随后的辐射强迫。该项目的第二阶段包括分析BC大小分布的可变性，以此作为格陵兰和南极洲现有冰芯BC来源和输送过程的潜在标志。该项目的主要目标是：1)验证最后一次冰川和前工业时代野火活动的模型模拟；2)量化野火对区域和全球气候的影响，包括从冰川到间冰期和从工业前到现在的时间尺度。研究人员的目标是计算变化的火焰对气溶胶辐射强迫、雪/冰反照率效应、海洋肥化和大气氧化能力的影响；以及3)检查在冰芯记录中观察到的BC颗粒大小的趋势，以评估冰川时期气候突变期间输送过程的变化，从而评估大规模气象过程的变化。这项分析的主要工具将是冰期化学和代理(ICECAP)模型，该模型是与之前的NSF基金一起开发的。潜在的更广泛的影响包括加强对温暖气候中火灾活动的理解，以帮助减少未来气候轨迹预测中的不确定性。该项目将通过NSF教师研究体验(RET)在哈佛大学的两个夏天为高中教师提供支持。RET的参与者将开发一门关于野火和气候的实践课程。该项目还将支持一名研究生和一名博士后研究员。

This project aims to examine the disparate records of past fire activity as a means to improve the understanding of variation in fire activity over time and climatic conditions. Wildfires have a large influence on regional and global climate change. Fires affect carbon storage, biogeochemical cycling, local hydrology, land albedo, ocean fertilization, and emissions of radiatively important gases and aerosols. Deposition of fire black carbon (BC) on snow and ice covered surfaces, for example, decreases albedo and leads to snow- and ice-melt, further loss of albedo, and subsequent warming. Despite the importance of fires to the earth-atmosphere system, knowledge of past fire activity is relatively scant. Ice-core records of carbon monoxide (CO) and BC in Antarctic ice cores do not show consistent trends over the last150 years, while trends in charcoal records and ice-core BC are sometimes at odds over longer timescales. Charcoal and BC records from the last glacial period reveal large variations tied to Dansgaard/Oeschger (D-O) events, but the climate implications of these variations are unknown.The first phase of the project involves the rigorous validation of a 250-year simulation of wildfire activity and climate feedbacks since 1750. After gaining confidence in model performance, the researchers will simulate wildfire activity and subsequent radiative forcing during selected phases of an idealized D-O event. The second phase of the project includes analyzing the variability in BC size distributions as a potential marker of BC sources and transport processes in existing ice cores from Greenland and Antarctica. The main objectives of the project are: 1) Validate model simulations of wildfire activity in the last glacial and preindustrial eras; 2) Quantify the impacts of wildfires on regional and global climate on glacial-to-interglacial and preindustrial-to-present-day timescales. The researchers aim to calculate the effects of changing fires on aerosol radiative forcing, snow/ice albedo effects, ocean fertilization, and the atmospheric oxidative capacity; and 3) Examine observed trends in BC particle size in the ice core record to assess changes in transport processes and hence large-scale meteorological processes over abrupt climate change during the glacial period. The main tool for this analysis will be the Ice-age Chemistry And Proxies (ICECAP) model, which was developed with prior NSF funding.The potential broader impacts include an enhanced understanding of fire activity in warm climates to help reduce uncertainties in future climate trajectory predictions. The project will support high school teachers during two summers at Harvard through the NSF Research Experience for Teachers (RET). Participants in RET will develop a hands-on curriculum on wildfires and climate. The project will also support a graduate student and a postdoctoral fellow.