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CO2之后最重要的温室气体。甲烷的增长正在增加，目前的增长速度太高，无法实现巴黎协定到2100年的气候变化目标。因此，在COP26上达成的2021年格拉斯哥气候公约中，100个国家承诺到2030年将其甲烷排放量削减30%，这是谈判的关键成果之一。鉴于人们对了解全球甲烷预算有更大的兴趣，必须对甲烷的所有来源和汇进行充分的量化，以包括地球庞大的陆地生态系统在调节大气交换方面的作用。这是因为生态系统容易受到各种变化因素的影响，其中许多因素可以改变任何与甲烷相关的生态系统功能，并可能对全球CH4预算和地球气候产生影响。在全球范围内，大气CH4汇占主导地位的CH4损失，与小得多的土壤汇CH4消费甲烷氧化菌被认为是唯一的陆地汇。然而，数据驱动的全球建模工作往往高估排放源约151 Tg与较小的大气“自上而下”得出的估计值相比，每年的温室气体排放量约为100万吨，这可能表明，一个重要的陆地CH4汇项要么数量不足，要么在全球CH4预算中缺失。我们只发现了地球系统中第二个陆地甲烷汇（Gauci et al Nature under review）和40多年来确定的甲烷预算的第一个新的主要组成部分：高地树木的木质表面（我们认为所有在自由排水，低地下水位土壤上的树木都是“高地”树木，而湿地或oodplain树木的面积要小得多，并排放甲烷）。我们保守的全球估计将这个“高地树木汇”（每年约50 Tg）作为潜在的大于全球土壤汇的大小，因此显然需要用从热带树木的树冠和树冠内收集的新数据来重新估计我们估计的高度不确定性。这将有助于我们了解树木是否是地球系统中重要的“缺失汇”。树冠和树冠的取样具有挑战性，因此在我们目前的估计中没有得到很好的体现，然而，我们认为，树冠和树冠的树枝和细枝的木质表面的CH4吸收量应该比我们目前的估计更大。此外，从全球变化的角度来看，这一新发现可能是重要的，因为与土壤汇不同，土壤汇在全球范围内没有变化，热带高地森林（大多数这种木质表面CH4汇所在地）由于砍伐森林和土地利用变化的影响正在减少。在天然林被作物或牧场取代的地方，CH4汇将减少。因此，砍伐森林是造成所观察到的大气CH4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和建模中的UX的实地测量，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”，随着时间的推移改变大气甲烷浓度的贡献，使我们可以根据格拉斯哥气候公约解决甲烷浓度的增长。