Quantifying the true carbon removal potential of enhanced rock weathering

为了实现联合国将全球变暖控制在2摄氏度以内的目标，我们不仅需要减少碳排放，还需要积极消除我们添加到大气中的部分二氧化碳(CO2)。为此，英国承诺到2050年积极减少约5000万吨二氧化碳。虽然已经提出了多种解决方案来实现这一点，但只有少数方案可以在足够大的规模上应用，从而对气候缓解做出有意义的贡献。其中一个解决方案是加速硅酸盐岩石风化(也称为增强岩石风化-ERW)，理论上可以在全球范围内减少约10%的年碳排放。二氧化碳溶解在水中，然后与硅酸盐岩石反应。然后，风化产物通过溪流和河流被输送到海洋，在那里碳被锁住数千年。这种反应主动地从大气中去除碳，同时释放出有益于植物的矿物质。在自然界中，这一过程非常缓慢，但只需将这些岩石粉碎成细小的粉尘，就可以加速这一过程，这些粉尘可以通过现有的农业设备在全球范围内分发。尽管战争遗留爆炸物有望缓解气候变化，但证明其有效性的大规模实验很少，而且岩尘对土壤和淡水的非目标影响也不为人所知。事实上，所有的风化产物，因为它们是通过土壤和河流中的水运输的，都可以与土壤本身、植物以及土壤和河水中的微生物相互作用。这种相互作用可能会使战争遗留爆炸物的效率降低数量级，使人对其作为一项全球负排放技术的实施产生怀疑。此外，以陆地和水食物网为基础的生物--植物和微生物--可能会受到战争遗留爆炸物的副作用的影响。然而，我们缺乏来自土壤和水生生物地球化学、生态学和水文学的必要的跨学科知识，无法充分了解和预测战争遗留爆炸物的效率。在这个项目中，我们召集了一个来自上述所有科学学科的专家团队，以全面了解战争遗留爆炸物的过程，从应用硅酸盐岩石粉尘到风化产物到达海洋。为了实现这一目标，我们将结合跨学科的实验技术、最先进的研究基础设施和计算模型。首先，我们将就岩石风化过程和不同的风化产物如何影响植物和土壤微生物以及如何影响这些植物和土壤微生物提供新的基础知识。伦敦帝国理工学院将进行一项旨在揭示土壤、植物和微生物影响的实验。然后，我们将提供有关风化产物如何与河水以及河水中的微生物相互作用的基本知识。为了做到这一点，将在伯明翰大学最先进的研究设施中进行一项实验，揭示河流水化学、河流水流动力学和水生微生物的影响。然后，我们将通过对战争遗留爆炸物进行全面的实地试验，并在威尔士森林中监测其效率的所有方面，将新知识从实验室推广到现实世界。最后，我们将把所有的新知识整合到一个先进的生态水文模型中，该模型可以用来预测流域尺度上的碳去除效率。该项目的最终成果将是对战争遗留爆炸物在英国消除二氧化碳的潜力的评估，以及它是否能为该国的气候目标做出重大贡献，以及利益攸关方可以用来可信地评估战争遗留爆炸物的碳去除效率的工具。这将是负责实现一个县负排放目标的州决策者和碳产业的重要资源。

To achieve the UN goal of less than 2 degrees of global warming, we need to not only reduce carbon emissions, but actively remove part of the carbon dioxide (CO2) we have added to the atmosphere. For this reason, the UK has committed to actively remove ~50 million tons of CO2 by 2050. While multiple solutions have been proposed to achieve this, only a handful can be applied at scales large enough to meaningfully contribute to climate mitigation. One of those solutions is the acceleration of silicate rock weathering (also called Enhanced Rock Weathering - ERW), which theoretically could globally remove ~10% of our annual carbon emissions. CO2 dissolves in water and then reacts with silicate rocks. The weathering products are then transported through streams and rivers to the ocean, where the carbon is locked away for thousands of years. This reaction actively removes carbon from the atmosphere, and at the same time it releases minerals that can benefit plants. In nature the process is very slow but can be sped up by simply crushing those rocks into a fine dust, which could be distributed by existing farming equipment at global scales. Despite the promise of ERW for climate mitigation, there are very few large-scale experiments which have demonstrated its efficacy, and non-target effects of rock dust on soils and fresh waters are not well known. In fact, all the weathering products, as they are transported via water in the soils and in the rivers, can interact with the soil itself, with plants, and with microorganisms living in soils and river water. This interaction may reduce the efficiency of ERW by orders of magnitude, casting doubt on its implementation as a global negative emission technology. Moreover, organisms at the basis of land and water food webs - plants and microbes - may be impacted by the side effects of ERW application. However, we lack the necessary interdisciplinary knowledge from soil and aquatic biogeochemistry, ecology and hydrology to fully understand and predict the efficiency of ERW. In this project we assemble a team of experts from all the aforementioned scientific disciplines to provide a complete understanding of the process of ERW, from the application of silicate rock dust until the weathering products reach the oceans. To achieve that, we will combine interdisciplinary experimental techniques, state of the art research infrastructure, and computational modelling. First, we will provide new fundamental knowledge on how the rock weathering process and the different weathering products affect and are affected by plants and soil microbes. An experiment that will disentangle the impacts of soils, plants and microbes will be conducted at Imperial College London. Then, we will provide fundamental knowledge on how the weathering products interact with river waters and the microorganisms living in them. To do that an experiment that disentangles the effects of river water chemistry, river flow dynamics, and aquatic microorganisms will be conducted at state-of-the art research facilities at the University of Birmingham. We will then generalize the new knowledge from the laboratory to the real world, by performing a full-scale field trial of ERW and monitoring all aspects of its efficiency in a Welsh forest. Finally, we will integrate all the new knowledge into an advanced ecohydrological model that can be used to predict the carbon removal efficiency at the catchment scale. The final deliverable of the project will be an assessment of ERW's potential to remove CO2 in the UK, and whether it can significantly contribute towards the country's climate goals, and tools that can be used by stakeholders to credibly assess the carbon removal efficiency of ERW. This will be an essential resource for state decision makers, in charge of meeting a county's negative emission goals, and the carbon industry.