Global‐Scale Evaluation of Coastal Ocean Alkalinity Enhancement in a Fully Coupled Earth System Model
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Abstract The Paris Agreement plans for “net‐zero” carbon dioxide (CO 2 ) emissions during the second half of the 21st century. However, reducing emissions from some sectors is challenging, and “net‐zero” permits carbon dioxide removal (CDR) activities. One CDR scheme is ocean alkalinity enhancement (OAE), which proposes dissolving basic minerals into seawater to increase its buffering capacity for CO 2 . While modeling studies have often investigated OAE at basin or global scale, some proposals focus on readily accessible coastal shelves, with TA added through the dissolution of seafloor olivine sands. Critically, by settling and dissolving sands on shallow seafloors, this retains the added TA in near‐surface waters in direct contact with atmospheric CO 2 . To investigate this, we add dissolved TA at a rate of ∼29 Teq y −1 to the global shelves (<100m) of an Earth system model (UKESM1) running a high emissions scenario. As UKESM1 is fully coupled, wider effects of OAE‐mediated increase in ocean CO 2 uptake –e.g. atmospheric xCO 2 , air temperature and marine pH– are fully quantified. Applying OAE from 2020 to 2100 decreases atmospheric xCO 2 ∼10 ppm, and increases air‐to‐sea CO 2 uptake ∼8%. In‐line with other studies, CO 2 uptake per unit of TA added occurs at a rate of ∼0.8 mol C (mol TA) −1 . Significantly for monitoring, advection of added TA results in ∼50% of CO 2 uptake occurring remotely from OAE operations, and the model also exhibits noticeable land carbon reservoir changes. While practical uncertainties and model representation caveats remain, this analysis estimates the effectiveness of this specific OAE scheme to assist with net‐zero planning.Keywords:
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Global biogeochemistry is the discipline that links various aspects of biology, geology, and chemistry to investigate the surface environment of the Earth. The global biogeochemical cycles of the elements lie at the very core of the subject and involve a myriad of processes that transform and transport various substances throughout the Earth's ecosphere, which consists of the atmosphere, hydrosphere, shallow crust (soils, sediments, and crustal rocks), biosphere, and cryosphere. As the authors of Biogeochemical Cycles: A Computer‐Interactive Study of Earth System Science and Global Change say, “anyone interested in understanding the causes of global environmental change and its implications for life would be well‐advised to begin with an investigation of global biogeochemistry.” This small but illuminating book is an attempt to provide a reasonably integrated and comprehensive text dealing with the study of the life‐essential global biogeochemical cycles of carbon, phosphorus, nitrogen, sulfur, and oxygen.
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At the Earth's surface, a complex suite of chemical, biological, and physical processes combines to create the engine that transforms bedrock into soil (Figure 1). Earth's weathering engine provides nutrients to nourish ecosystems and human society mediates the transport of toxic components within the biosphere, creates water flow paths that carve and weaken bedrock, and contributes to the evolution of landscapes at all temporal and spatial scales. At the longest time scales, the weathering engine sequesters CO 2 , thereby influencing long‐term climate change. Despite the importance of soil, our knowledge of the rate of soil formation is limited because the weathering zone forms a complex, ever‐changing interface, and because scientific approaches and funding paradigms have not promoted integrated research agendas to investigate such complex interactions. No national initiative has promoted a systems approach to investigation of weathering science across the broad array of geology, soil science, ecology and hydrology. Such a program is certainly needed, and this article describes a platform on which to build the initiative to answer the following question: How does the Earth weathering engine break down rock to nourish ecosystems, carve errestrial landscapes, and control carbon dioxide in the global atmosphere?
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The capacity for tipping points in the climate system was elucidated decades ago by numerical climate models, which showed that nonlinearities could arise from physical interactions between the ocean, sea ice, and atmospheric components, leading to rapid shifts between qualitatively different states. However, there has been comparatively little work on physical interactions with the human component of the Earth system through numerical modeling due, in part, to the rarity of inclusion of the human system directly in Earth system models. Earth System economics provides a new approach for doing so, by proposing a particular set of physical variables that can be used as a basis for simulating such changes. These variables include spatially resolved population demography, time allocation to activities, a spatially resolved technosphere, and spatial networks that capture transportation fluxes. New global compilations of time use and technosphere data are helping to enable this approach, by quantifying the dependencies of material fluxes on time use and context. This opens the possibility of simulating long-term dynamics through motivated changes to time allocation, with outcomes dependent on the evolution of the technosphere and other coupled features of the Earth system. Examples will be discussed regarding how this approach can provide holistic, physically-grounded ways to identify possible nonlinearities and tipping points, by explicitly resolving aspects of human activities and technosphere changes, constrained by the conservation of mass, energy, and time.
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Understanding human-environment feedbacks is becoming increasingly important as climate change mitigation and adaptation strategies continue to diversify, target new areas, and grow in extent. Incorporating these feedbacks into models is critical for assessing the effectiveness of such strategies and how they may change in response to a changing climate. For example, projected forest expansion varies with changing climate because climate-driven changes in forest productivity affect the cost-effectiveness of reforestation strategies. Including human-environment feedbacks in models can dramatically change the projected scenario as human systems respond to the changing environment, which in turn affects the Earth system projection. We have incorporated human-Earth feedbacks in a synchronously coupled system comprising the Global Change Analysis Model (GCAM) and the Energy Exascale Earth System Model (E3SM). GCAM is the core model in a new E3SM human component that is at the same level as the Earth model components (land, atmosphere, ocean, etc.) and interacts with them through the shared coupling software. Terrestrial productivity is passed from E3SM to GCAM to make climate-responsive land use and CO2 emission projections for the next five-year period, which are interpolated and passed to E3SM annually. Previous experiments with a similar model have shown that the incorporation of these feedbacks affects land use/cover change, crop prices, terrestrial carbon, local surface temperature, and land carbon-atmosphere feedbacks. Preliminary results indicate that this newly coupled system is robust in relation to the previous experiments. The human scenario is altered by terrestrial feedbacks, which in turn changes the Earth system projections. Regional differences are more pronounced than global differences due to regional shifts in land use. This new coupling addresses inconsistency across models, enables a new type of scenario development, and provides a modeling framework that is more easily updated and expanded.
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Both the earth surface system and the history of geology have the characteristics of interfacing between natural and social sciences. The content and the aim of research on these two fields are related each other. They reveal from different view points the objective regularities of various geological functions and geological processes to promote the harmonic development between humans and nature. Among all the geological disciplines of Earth surface system, regional tectonics occupies an important position. Therefore the discussion on the research history of the regional tectonics in China is significant in the study of the history of geology. The paper delineates the 6 research stages for the regional tectonics in China, summarizes experiences and progressions, and indicates that the social environment, guidelines in the scientific research, the level of contemporary science and technology and the way of thinking are the key factors determining the development of the scientific research. In the 21st century, earth surface system becomes one of the major research fields in the earth sciences. The research of regional tectonics in China has to merge with the study of earth surface system.
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Earth system science (ESS) is an approach to: ‘obtain a scientific understanding of the entire Earth system on a global scale by describing how its component parts and their interactions have evolved, how they function, and how they may be expected to continue to evolve on all timescales’ (Bretherton, 1998). The aim of this review is to introduce some key examples showing the role of Earth surface processes, the traditional subject of geomorphology, within the interacting Earth system. The paper considers three examples of environmental systems in which geomorphology plays a key role: (1) links between topography, tectonics, and atmospheric circulation; (2) links between geomorphic processes and biogeochemical cycles; and (3) links between biological processes and the Earth’s surface. Key research needs are discussed, including the requirement for better opportunities for interdisciplinary collaboration, clearer mathematical frameworks for Earth system models, and more sophisticated interaction between natural and social scientists.
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