Constraining the carbon cycle during glacial-interglacial CO2 change

目前的化石燃料排放正在导致大气、海洋和陆地上二氧化碳的自然平衡发生变化。大气中的二氧化碳水平正以前所未有的速度上升，由于碳吸收，海洋正变得更加酸性。预计的气候变化将改变陆地生态系统储存碳的能力。由于大气二氧化碳水平、气候、陆地生态系统和海洋环流之间的复杂相互作用，对今天的化石燃料排放将如何改变未来世界的预测非常不确定。然而，今天化石燃料排放的后果在未来几十年和几个世纪可能会给人类带来巨大的影响。今天并不是大气二氧化碳和气候发生变化的唯一已知时间段。在80万年前被困在极地冰芯中的气泡中，二氧化碳浓度得到了测量。这些气泡表明，随着地球气候在冰期和暖期之间发生变化，大气中的二氧化碳水平曾多次波动。研究发现，温暖时期的二氧化碳水平比冰河时期高出约40%。这些二氧化碳增加被认为既是气候变暖的原因(通过温室效应)，也是由气候变暖引起的。当大气二氧化碳水平较低时，海洋储存的碳较多，而当大气二氧化碳水平较高时，海洋储存的碳较少。然而，气候变化改变大气二氧化碳水平的确切机制仍不清楚。识别这些机制不仅有助于我们了解过去，也将有助于我们了解今天化石燃料排放可能产生的未来后果。这项提议旨在限制过去冰期-间冰期大气二氧化碳变化的可能原因。将提出两个具体的研究问题。首先，到底需要收集什么新数据才能准确地限制二氧化碳变化的原因？现有的碳循环数据无法区分二氧化碳变化的相互竞争的解释：许多替代解释似乎都与数据一致。为了知道什么解释真正解释了冰期-间冰期二氧化碳的变化，我们需要确定只与一种可能的解释相一致的数据。这项研究提案将实施一种基于矩阵的新方法，以确定需要哪些新数据来测试替代解释。其次，这项提案将回答“为什么不同类型的海洋计算机模型似乎以不同的方式储存碳？”将利用最新的理论进展，使计算机模型中的碳储存能够以一种新的定量方式进行分析。在我们了解海洋模型之间的差异之前，我们无法理解真正的海洋是如何储存碳的，以及这种碳储存是如何在冰期-间冰期循环中发生变化的。气候变化和从末次冰期向现代暖期过渡时的碳循环是当前系统的一个重要类比。我们应该期待气候对我们人类的碳排放有多敏感？作为回报，未来的碳循环对化石燃料引发的气候变化会有多敏感？更好地理解过去冰期和暖期之间的自然碳循环行为，将有助于改进对未来气候和碳循环的预测。反过来，这将有助于我们了解我们在化石燃料排放方面所做选择的可能结果。

Current fossil fuel emissions are leading to changes in the natural balance of carbon dioxide in the atmosphere, ocean and on land. Atmospheric carbon dioxide levels are rising at an unprecedented rate and the ocean is becoming more acidic due to carbon uptake. Projected climate change is due to alter the ability of terrestrial ecosystems to store carbon. Due to the complex interactions between atmospheric carbon dioxide levels, climate, terrestrial ecosystems and ocean circulation, predictions about how today's fossil fuel emissions will alter the future world are very uncertain. Yet the consequences of today's fossil fuel emissions could be great for humankind in the coming decades and centuries. The present day is not the only known time period in which atmospheric carbon dioxide and climate have changed. Carbon dioxide concentrations have been measured within air bubbles that became trapped in polar ice cores dating back up to 800 000 years. These air bubbles reveal that atmospheric carbon dioxide levels have fluctuated many times as the Earth's climate has changed between ice ages and warm periods. Carbon dioxide levels are found to have been about 40% higher during warm periods than during ice ages. These carbon dioxide increases are thought to both contribute to the warmer climates (through the greenhouse effect) and have been caused by the warmer climates. When atmospheric carbon dioxide levels were low, the ocean stored more carbon, and when atmospheric levels were high the ocean stored less carbon. However, the precise mechanisms by which changes in climate alter atmospheric carbon dioxide levels remain unknown. Identifying these mechanisms will not only help us to understand the past, but will also help to us understand the likely future consequences of today's fossil fuel emissions. This proposal aims to constrain the possible causes of the past glacial-interglacial changes in atmospheric carbon dioxide. Two specific research questions will be posed. Firstly, precisely what new data needs to be gathered to accurately constrain the causes of carbon dioxide changes? The existing carbon-cycle data cannot distinguish between competing explanations of carbon dioxide change: many alternative explanations all appear to agree with the data. In order to know what explanation truly explains the glacial-interglacial CO2 change, we need to identify data that will agree with only one of the possible explanations. This research proposal will implement a novel matrix based method to determine what new data is required to test the alternative explanations. Secondly, this proposal will answer 'why do different types of computer models of the ocean appear to store carbon in different ways?' Recent theoretical advances will be utilised, which allow carbon storage in computer models to be analysed in a new quantitative way. Until we understand the differences between ocean models, we cannot understand how the real ocean stores carbon, and how this carbon storage changed over glacial-interglacial cycles. The coupled changes in climate and the carbon cycle at the transition from the last ice-age to the modern warm period are an important analogue for the present system. Just how sensitive should we expect climate to be to our human carbon emissions? And, in return, how sensitive to the fossil fuel induced climate change will the future carbon cycle be? A better understanding of natural carbon cycle behaviour, during the transition between past ice-ages and warm periods, will help to improve predictions about the future of climate and the carbon cycle. This will, in turn, help to inform us of the likely outcomes of the choices we make regarding fossil fuel emissions.