RELEASING DIVALENT CATIONS TO SEQUESTER CARBON ON LAND AND SEA

碳循环对大气中二氧化碳增加引起的变暖的自然反应具有两种从大气中去除二氧化碳的负反馈。一种是由于海洋酸度增大，碳酸盐矿物被溶解，导致海水含碳能力增加（以碳酸氢盐离子的形式）。另一种是在更温暖的条件下增加硅酸盐矿物的溶解速度，其产物要么沉淀为碳酸盐矿物，要么流入海洋。这种硅酸盐的风化作用也会从大气中去除二氧化碳。有意加速这两种风化反馈是一种潜在的方法，可以消除化石燃料燃烧向大气中添加的二氧化碳，从而缓解极端气候变化。然而，这种方法是具有挑战性的，因为要在相当大的范围内（例如1-10 GtC / pa去除）使用，需要相对于自然速率大幅增加风化作用。这种加速风化是否是去除大气中大量二氧化碳的可行途径尚不清楚。本提案将解决这一未知问题，并对加速风化去除二氧化碳的可行性进行全面评估，包括对该方法的技术、经济、环境和社会方面的考虑。我们工作的核心将是对增强风化方法的生命周期评估，这可能导致每年1-10Gt的二氧化碳去除。这个模型将从风化矿物的可用性开始，特别关注但不是唯一关注来自采矿等行业的废料。它将审议如何通过在采矿废料堆中进行处理，或与项目伙伴合作，除土壤外，如何加强这些矿物的风化作用。它还将考虑风化物质的命运，要么作为陆地或海洋中的碳酸盐，要么作为海洋中的碱度。它将评估这些方法的经济成本、能源需求、它们将造成的环境破坏以及对这些方法的社会限制（例如社会可接受性、政治、法律、治理）。在一些关键领域，理解还不足以进行生命周期评估。我们将通过五个具体的研究来解决这些知识空白。这些将:1。描述有多少废物可用于增强风化，包括其位置，粒度，化学和矿物学。这是支持生命周期评估的关键信息。测量典型矿物的风化速度，以及这种风化速率如何随温度变化，特别是通过添加已知会导致硅酸盐加速风化的微生物。评估如何最好地将风化放大到1-10GtC / pa的水平。这将通过对可能的工程风化方法进行建模，以及对硅酸盐和碳酸盐矿物堆（每堆10立方米）进行实验来完成，在这些实验中，条件被改变，反应被测量。评估海洋对因风化作用增强而导致的碱度增加的反应。如果海洋中产生了更多的碳酸盐，就会降低增强风化作用的有效性；我们将测量无机碳酸盐和生物碳酸盐的形成速率及其对全球C循环的影响。考虑社会将如何应对加速风化的可能情况，以及这是否会限制这种方法。增强的风化能被社会所接受吗？是否有实现这一目标的政治意愿？它们是否存在法律或治理障碍？来自这五个“研究组成部分”的信息将为生命周期评估提供关键信息，从而使增强风化CO2去除的总体潜力和挑战得到充分评估。

The natural response of the carbon cycle to the warming induced by increased atmospheric CO2 features two negative feedbacks that remove CO2 from the atmosphere. One, caused by the greater acidity of the oceans, is for carbonate minerals to be dissolved, which causes an increase in the ability of seawater to contain carbon (as the bicarbonate ion). The other is for warmer conditions to increase the rate at which silicate minerals dissolve, with the products either precipitated as carbonate minerals, or flowing to the oceans. This silicate weathering also removes CO2 from the atmosphere.Intentional acceleration of these two weathering feedbacks is a potential approach to remove the CO2 added to the atmosphere by burning of fossil fuels, and therefore alleviate extreme climate change. Such an approach is challenging, however, because to be useful at a significant scale (i.e. 1-10 GtC pa removal), requires a dramatic increase in weathering relative to natural rates. Whether such accelerated weathering is a feasible route to remove significant atmospheric CO2 is unknown. This proposal will address this unknown, and provide a comprehensive assessment of the feasibility of CO2 removal by accelerated weathering, including consideration of the technical, economic, environmental, and societal aspects of the approach.The core of our work will be a life-cycle assessment of the enhanced-weathering approaches that might lead to 1-10Gt removal of CO2 per year. This modelling will start from the availability of minerals for weathering, paying particular but not exclusive attention to waste materials from industries such as mining. It will consider how the weathering of these minerals might be enhanced, either through treatment in mining waste piles or, in collaboration with project partners, by addition to soils. It will also consider the fate of the weathered materials, either as carbonate on land or in the sea, or as alkalinity in the sea. It will assess the economic cost of such approaches, the energy requirements, the environmental damage they would cause, and the societal limitations on such approaches (e.g. social acceptability, political, legal, governance).In some key areas, understanding is not yet sufficient to allow this life-cycle assessment. We will address these gaps in knowledge by five specific pieces of research. These will:1. Characterise how much waste material is available for enhanced weathering, including its location, its grain size, and its chemistry and mineralogy. This is critical information to underpin the life-cycle assessment.2. Measure how quickly typical minerals weather and how this weathering rate changes with temperature and, particularly, through addition of microbes that are known to cause accelerated weathering of silicates.3. Assess how best to scale up weathering to the 1-10GtC pa level. This will be done by both modelling of possible engineered approached to weathering, and by experiments on piles of silicate and carbonate minerals (each of 10 cubic meters), in which the conditions are altered and responses measured.4. Assess the response of the ocean to increased alkalinity resulting from enhanced weathering. If more carbonate is produced in the ocean, it reduces the effectiveness of enhanced weathering; we will measure the rates of both inorganic and biological carbonate formation and their impact in the C cycle globally.5. Consider how society will response to possible scenarios for accelerated weathering, and whether this may limit such an approach. Will enhanced weathering be socially acceptable? Will there be the political will to pursue it? Are their legal or governance barriers?Information from these five "research components" will provide critical information for the life-cycle assessment, and thereby allow the overall potential and challenge of enhanced weathering CO2 removal to be fully assessed.