Is Tropical Deforestation Contributing To The Rise In Atmospheric Methane? (DefMet)

热带森林砍伐是否导致大气甲烷含量上升？

• 批准号: NE/Z000025/1
• 负责人: Vincent Gauci
• 金额: $ 107.01万
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FZ000025%2F1
• 关键词: Tropical; Deforestation; Contributing; Rise; Atmospheric

Methane (CH4) is the most important anthropogenically enhanced greenhouse gas in the atmosphere after CO2. Growth in CH4 is increasing, and is currently tracking too high to meet Paris Agreement targets on climate change by 2100. As a result, in the 2021 Glasgow Climate Pact agreed at COP26, 100 countries pledged 30% cuts to their CH4 emissions by 2030, one of the key outcomes of the talks. Given this greater interest in understanding the global methane budget, it essential that all sources and sinks of methane are fully quantied to include the role of Earth's vast terrestrial ecosystems in mediating atmospheric exchange. This is because ecosystems are vulnerable to various agents of change, many of which can alter any methane- relevant ecosystem function with potential knock on eects for the global CH4 budget and Earth's climate. Globally, the atmospheric CH4 sinks dominate CH4 losses, with the farsmaller soil sink where CH4-consuming methanotrophs are considered the only terrestrial sink. However, data-driven global modelling eorts tend to over-estimate emission sources by ~151 Tg (million tonnes) each year when compared to smaller atmospheric 'top-down' derived estimates, possibly suggesting that a substantial terrestrial CH4 sink term is either poorly quantied or missing from the global CH4 budget.This year, we have discovered only the second terrestrial CH4 sink in the Earth system (Gauci et al Nature under review) and the rst new major component of the methane budget to be identied for over 40 years: The woody surfaces of upland trees (we consider all trees on free draining, low water-table soils as 'upland' trees in contrast to wetland or oodplain trees which are far smaller in area and emit methane). Our conservative global estimate places this 'upland tree sink' (~50Tg each year) as potentially larger than the size of the global soil sink so there is a clear need to rene the high degree of uncertainty in our estimate with new data gathered from within the crowns and canopies of tropical trees. This will help us to see if trees are an important 'missing sink' in the Earth system. The crowns and canopies of trees are challenging to sample from and so are not well represented in our current estimates, however, our datasuggest that CH4 uptake should be larger on the woody surfaces of branches and twigs of tree crowns and canopies, than our current estimates assume. Further, this new discovery may be important from a global change perspective since, unlike the soil sink, which is not changing in global area, tropical upland forests (where the majority of this woody surface CH4 sink resides) are declining due to the eects of deforestation and land use change. Where natural forest is replaced with crops or pasture, the CH4 sink will be reduced. Deforestation is therefore a potential additional mechanism responsible for observed ongoing growth in atmospheric CH4 concentration. We propose to examine the full role of natural tropical upland forest in the methane cycle through a combination of eld measurements of uxes in West African trees and modelling. The result will be better understanding of the contribution of trees anddeforestation, the "new methane sink", to changing atmospheric methane concentrations over time so that we may address growth in CH4 concentration in accordance with the Glasgow Climate Pact.

甲烷 (CH4) 是继二氧化碳之后大气中最重要的人为增强温室气体。 CH4 的增长正在增加，目前的增长速度过高，无法在 2100 年之前实现《巴黎协定》关于气候变化的目标。因此，在 COP26 上商定的 2021 年格拉斯哥气候公约中，100 个国家承诺到 2030 年将 CH4 排放量削减 30%，会谈的主要成果之一。鉴于人们对了解全球甲烷预算的兴趣更大，有必要对所有甲烷源和汇进行全面量化，以包括地球广阔的陆地生态系统在调节大气交换中的作用。这是因为生态系统容易受到各种变化因素的影响，其中许多变化因素可能会改变任何与甲烷相关的生态系统功能，并对全球甲烷预算和地球气候产生潜在的连锁影响。在全球范围内，大气中的 CH4 汇在 CH4 损失中占主导地位，而土壤汇要小得多，其中消耗 CH4 的甲烷氧化菌被认为是唯一的陆地汇。然而，与较小的大气“自上而下”推算相比，数据驱动的全球建模工作往往每年高估排放源约 151 Tg（百万吨），这可能表明大量的陆地 CH4 汇项要么很差，要么不太好。全球 CH4 预算中已量化或缺失。今年，我们仅发现了地球系统中的第二个陆地 CH4 汇（Gauci 等人《Nature》正在审查中）和甲烷预算的第一个新的主要组成部分40多年来一直被识别：高地树木的木质表面（我们将自由排水、低地下水位土壤上的所有树木视为“高地”树木，与面积小得多并排放甲烷的湿地或冲积平原树木形成鲜明对比） 。我们保守的全球估计认为这个“高地树木汇”（每年约 50Tg）可能大于全球土壤汇的大小，因此显然需要利用从内部收集的新数据来重新调整我们估计中的高度不确定性热带树木的树冠和树冠。这将帮助我们了解树木是否是地球系统中重要的“缺失的汇”。树冠和树冠的采样具有挑战性，因此在我们当前的估计中没有得到很好的体现，但是，我们的数据表明，树冠和树冠的树枝和细枝的木质表面吸收的 CH4 应该比我们当前的估计更大认为。此外，从全球变化的角度来看，这一新发现可能很重要，因为与全球范围内没有变化的土壤汇不同，热带高地森林（大部分木质表面 CH4 汇所在的地方）由于以下因素的影响而正在减少：森林砍伐和土地利用变化。当天然林被农作物或牧场取代时，CH4 汇将会减少。因此，森林砍伐是造成大气中甲烷浓度持续增长的一个潜在的额外机制。我们建议通过结合西非树木通量的现场测量和建模来研究天然热带高地森林在甲烷循环中的全部作用。其结果将是更好地了解树木和森林砍伐（“新的甲烷汇”）对随时间变化的大气甲烷浓度的贡献，以便我们可以根据《格拉斯哥气候公约》解决甲烷浓度的增长问题。