Constraining Arctic Carbon-Cycle Feedbacks

北极永久冻土覆盖了地球上的大片区域，是英国的60多倍，那里的气温如此之低，以至于地面常年结冰。这意味着土壤有记忆：生活在数千年前并被埋在土壤中的动植物一直冻结在那里，没有完全腐烂。随着时间的推移，这种情况一直在持续，地下积累了大量的有机物质。永久冻土形成一层固体，导致地表积水，这也阻止了有机物的分解。全球变暖已经开始融化永久冻土，而且这种情况将继续下去。随着土壤融化，微生物开始分解之前冻结和受涝的有机物质，将其转化为温室气体：二氧化碳和甲烷。总体而言，北极土壤中的碳比整个大气中的碳都多，这使得融化的永久冻土有可能大量释放温室气体。这意味着，由人类造成的任何变暖都可能被来自永久冻土层的额外温室气体放大。因此，了解冻土排放对全球变暖的影响，对于确定我们是否能达到国际气候目标至关重要，比如巴黎协议中的目标。研究表明，到本世纪末，冻土排放的温室气体可能会导致全球变暖增加0.8摄氏度。然而，这一数字高度不确定，需要进一步研究才能了解其中涉及的机制。我的项目将解决关键的悬而未决的问题：土壤中有多少有机物质会分解，分解的速度有多快？它会导致多大程度的全球变暖？植物会在更温暖的北极生长得更好吗？这能弥补永久冻土释放的温室气体吗？我将研究全球模式，以确定北极土壤在更温暖的气候下会是什么样子。没有永久冻土的土壤往往比北极土壤储存的有机物质少。通过分析全球范围内有机质与气温和降雨量等因素的关系，我将开发一种新的方法来估计土壤有机质。然后，使用最新气候模型对未来气候的预测，我将估计北极的有机物质在全球变暖下将如何变化，并由此估计大约有多少温室气体将被释放。然后，我将与实地测量合作，开发一个复杂的模型来模拟北极的未来。朱尔斯是英国气候模型的一部分；它是整个地球陆地表面的模型。我将纳入目前没有包括在Jules模型中的关键过程，从而产生一个能够模拟最重要的北极过程的新模型版本。基于对北极新测量的最新科学理解，我将制定创新的方案，以代表：1)永久冻土中的水分分布(包括内涝)，2)北极植物物种，3)土壤中有机物的分解。未来总是不确定的，这意味着不可能对未来北极的温室气体排放给出一个准确的值，而是给出一个范围的值。我将使用数学技术来解决这个问题，这些技术将观测中包含的信息转化为Jules模型本身中的一系列不确定性：本质上回答了这样一个问题：如果数据给我们提供了关于现实世界的一定量信息，那么与此相一致的可能模型的范围是多少？然后，我将对所有模型进行模拟，以估计全套可能的未来。这将模拟下个世纪北极的主要变化：永久冻土融化，植被转移，以及陆地表面二氧化碳和甲烷的交换。最终，这将导致对北极温室气体平衡以及北极在全球气候变化中的作用的更深入的理解。

Arctic permafrost covers a vast area of the Earth, more than 60 times the size of the UK, where temperatures are so low that the ground is frozen year-round. This means that the soil has a memory: plants and animals that lived thousands of years ago and were buried in the soil have remained frozen there, without fully decomposing. This has continued over time, and huge stores of organic matter have built up in the ground. Permafrost forms a solid layer, causing water-logging at the surface, which also stops the organic matter from decomposing.Global warming has started to thaw the permafrost, and this is set to continue. As the soil thaws, microbes start to decompose the previously-frozen and waterlogged organic matter, turning it into greenhouse gases: carbon dioxide and methane. In total, there is more carbon in Arctic soils than in the whole atmosphere, which gives the potential for massive release of greenhouse gases from thawing permafrost. This means any warming caused by humans may be amplified by extra greenhouse gases from the permafrost. Understanding the global warming impact from permafrost emissions is therefore crucial in determining whether we can meet international climate targets, such as those in the Paris agreement.Studies show that greenhouse gas emissions from permafrost could cause up to 0.8C additional global warming by the end of the century. However, this figure is highly uncertain and further research is required to understand the mechanisms involved. My project would address vital unanswered questions: How much of the organic matter in the soil will decompose, and how quickly? How much global warming will it cause? Will plants grow better in a warmer Arctic, and does this compensate for the greenhouse gases released from permafrost?I will study global patterns to determine how Arctic soils might look in warmer climates. Soils without permafrost tend to store less organic matter than Arctic soils. By analysing how the organic matter is related to factors like air temperature and rainfall on a global scale, I will develop a new way to estimate soil organic matter. Then, using predictions of future climate from the latest climate models, I will estimate how organic matter in the Arctic will change under global warming, and from this, approximately how much greenhouse gas would be released.I will then work with field measurements to develop a sophisticated model to simulate the future of the Arctic. JULES is part of the UK's climate model; it's a model of the land surface of the whole Earth. I would incorporate key processes that are currently not included in the JULES model, resulting in a new model version capable of simulating the most important Arctic processes. Based on the latest scientific understanding from new measurements in the Arctic, I would develop innovative schemes to represent: 1) Water distribution (including waterlogging) in permafrost soils, 2) Arctic plant species, 3) decomposition of organic matter in the soil.The future is always uncertain, which means that it is not possible to put an exact value on future greenhouse gas emissions from the Arctic, but rather to give a range of values. I will approach this using mathematical techniques that translate the information contained in observations into a range of uncertainty within the JULES model itself: Essentially answering the question, if data gives us a certain amount of information about the real world, what is the range of possible models that is consistent with this? I will then run simulations with the full range of models to estimate the full set of possible futures. This will simulate the major changes in the Arctic over the next century: thawing permafrost, shifting vegetation, and exchanges of carbon dioxide and methane from the land surface.Ultimately this will lead to a more robust understanding of the greenhouse gas balance in the Arctic, and the role of the Arctic in global climate change.