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Abstract To achieve net zero carbon emissions by mid-century, the United States may need to rely on carbon dioxide removal (CDR) to offset emissions from difficult-to-decarbonize sectors and/or shortfalls in near-term mitigation efforts. CDR can be delivered using many approaches with different requirements for land, water, geologic carbon storage capacity, energy, and other resources. The availability of these resources varies by region in the U.S. suggesting that CDR deployment will be uneven across the country. Using the global change analysis model for the United States (GCAM-USA), we modeled six classes of CDR and explored their potential using four scenarios: a scenario where all the CDR pathways are available (Full Portfolio), a scenario with restricted carbon capture and storage (Low CCS), a scenario where the availability of bio-based CDR options is limited (Low Bio), and a scenario with constraints on enhanced rock weathering (ERW) capabilities (Low ERW). We find that by employing a diverse set of CDR approaches, the U.S. could remove between 1 and 1.9 GtCO2/yr by midcentury. In the Full Portfolio scenario, direct air carbon capture and storage (DACCS) predominates, delivering approximately 50% of CO2removal, with bioenergy with carbon capture and storage contributing 25%, and ERW delivering 11.5%. Texas and the agricultural Midwest lead in CDR deployment due to their abundant agricultural land and geological storage availability. In the Low CCS scenario, reliance on DACCS decreases, easing pressure on energy systems but increasing pressure on the land. In all cases CDR deployment was found to drive important impacts on energy, land, or materials supply chains (to supply ERW, for example) and these effects were generally more pronounced when fewer CDR technologies were available.
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Increased carbon capture by a silicate-treated forested watershed affected by acid deposition
Abstract. Meeting internationally agreed-upon climate targets requirescarbon dioxide removal (CDR) strategies coupled with an urgent phase-down offossil fuel emissions. However, the efficacy and wider impacts of CDR arepoorly understood. Enhanced rock weathering (ERW) is a land-based CDRstrategy requiring large-scale field trials. Here we show that a low 3.44 t ha−1 wollastonite treatment in an 11.8 ha acid-rain-impacted forested watershed in New Hampshire, USA, led to cumulative carbon capture by carbonic acid weathering of 0.025–0.13 t CO2 ha−1 over 15 years. Despite a 0.8–2.4 t CO2 ha−1 logistical carbon penalty from mining,grinding, transportation, and spreading, by 2015 weathering together withincreased forest productivity led to net CDR of 8.5–11.5 t CO2 ha−1. Our results demonstrate that ERW may be an effective, scalableCDR strategy for acid-impacted forests but at large scales requiressustainable sources of silicate rock dust.
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- PAR ID:
- 10214831
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 18
- Issue:
- 1
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 169 to 188
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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As climate mitigation efforts lag, dependence on anthropogenic CO2removal increases. Enhanced rock weathering (ERW) is a rapidly growing CO2removal approach. In terrestrial ERW, crushed rocks are spread on land where they react with CO2and water, forming dissolved inorganic carbon (DIC) and alkalinity. For long-term sequestration, these products must travel through rivers to oceans, where carbon remains stored for over 10,000 years. Carbon and alkalinity can be lost during river transport, reducing ERW efficacy. However, the ability of biological processes, such as aquatic photosynthesis, to affect the fate of DIC and alkalinity within rivers has been overlooked. Our analysis indicates that within a stream-order segment, aquatic photosynthesis uptakes 1%–30% of DIC delivered by flow for most locations. The effect of this uptake on ERW efficacy, however, depends on the cell-membrane transport mechanism and the fate of photosynthetic carbon. Different pathways can decrease just DIC, DIC and alkalinity, or just alkalinity, and the relative importance of each is unknown. Further, data show that expected river chemistry changes from ERW may stimulate photosynthesis, amplifying the importance of these biological processes. We argue that estimating ERW’s carbon sequestration potential requires consideration and better understanding of biological processes in rivers.more » « less
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Concern over the impacts of anthropogenic greenhouse gas emissions has led to proposals to offset CO2 emissions by mechanisms that could increase carbon storage in soils. Estimates of the potential efficacy of various strategies vary, but an issue common to all of them is how to verify the magnitude and stability of the results of interventions. Soil sinks are “out of sight” which contrasts with strategies like reforestation. Below-ground carbon sinks, whether they be organic or inorganic, pose substantially more challenging issues for quantification and monitoring. ERW seeks to apply Ca, Mg-rich silicate rocks to enhance the consumption of CO2 by weathering reactions. Measurement of base cation losses from soils is used for quantifying CO2 uptake. Assessing CO2 uptake this way requires assessment of small differences between heterogeneous end members. Geochemical tracers can be used to estimate basalt input assuming that the endmembers are distinct. To compensate for open system behavior normalization to an “immobile” element is necessary. The limitation is typically the highly heterogenous nature of soils. Data from these settings often have high covariances. We reanalyzed published data on amended soils using Monte Carlo uncertainty analysis. We find that in a number of cases the Ca and Mg differences in pre- and post-amendment soils are not significantly different from zero (1 s.e.). High soil chemistry variances makes quantification of small differences difficult. Techniques for estimating relevant sample size and power for noisy data sets and modest effect sizes are well developed in other fields and can be appropriately applied to ERW problems. A simplified example using Lehr’s approximate rule for a two-sided test with s.d. for the pre- and post- data sets = 0.1 and the effect size (net change) = 0.03 yields a sample size n = 178 to obtain a sample power of 0.8 at the 95% CI, an optimistic estimate. Appropriate experimental design for ERW will require substantial sampling effort and rigorous a priori statistical assessment. Current studies so far cannot achieve this. The ocean ∆CO2/∆ALK ratio used to estimate CO2 uptake is important and unlikely to be as high as most studies have assumed.more » « less
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Concern over the impacts of anthropogenic greenhouse gas emissions has led to proposals to offset CO2 emissions by mechanisms that could increase carbon storage in soils. Estimates of the potential efficacy of various strategies vary, but an issue common to all of them is how to verify the magnitude and stability of the results of interventions. Soil sinks are “out of sight” which contrasts with strategies like reforestation. Below-ground carbon sinks, whether they be organic or inorganic, pose substantially more challenging issues for quantification and monitoring. ERW seeks to apply Ca, Mg-rich silicate rocks to enhance the consumption of CO2 by weathering reactions. Measurement of base cation losses from soils is used for quantifying CO2 uptake. Assessing CO2 uptake this way requires assessment of small differences between heterogeneous end members. Geochemical tracers can be used to estimate basalt input assuming that the endmembers are distinct. To compensate for open system behavior normalization to an “immobile” element is necessary. The limitation is typically the highly heterogenous nature of soils. Data from these settings often have high covariances. We reanalyzed published data on amended soils using Monte Carlo uncertainty analysis. We find that in a number of cases the Ca and Mg differences in pre- and post-amendment soils are not significantly different from zero (1 s.e.). High soil chemistry variances makes quantification of small differences difficult. Techniques for estimating relevant sample size and power for noisy data sets and modest effect sizes are well developed in other fields and can be appropriately applied to ERW problems. A simplified example using Lehr’s approximate rule for a two-sided test with s.d. for the pre- and post- data sets = 0.1 and the effect size (net change) = 0.03 yields a sample size n = 178 to obtain a sample power of 0.8 at the 95% CI, an optimistic estimate. Appropriate experimental design for ERW will require substantial sampling effort and rigorous a priori statistical assessment. Current studies so far cannot achieve this. The ocean ∆CO2/∆ALK ratio used to estimate CO2 uptake is important and unlikely to be as high as most studies have assumed.more » « less
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Although many sources of atmospheric CO2 have been identified, the major sinks are best understood in a deep-time context. Here, we focus on two Large Igneous Provinces (LIPs), the Central Atlantic Magmatic Province (CAMP) situated in the low latitude humid zone ~201.6 Ma and the Karoo-Ferrar located at high southern latitudes ~183 Ma. We use soil carbonate, lithologic, δD of n-alkanes, Sr data, and modeling to examine how these eruptions, hydrological cycling, and weathering impacted global atmospheric CO2, carbon cycling, and biotic extinction at the ETE and T-OAE hyperthermals. CAMP largely erupted in the tropics, doubled atmospheric CO2 from ~2,500 – 5,000 ppm at the ETE (observed in soil carbonates with an onset <1000 and a duration of <~20 ky) and rapidly sequestered CO2 (< 2,500 ppm) as recorded in Newark Supergroup basins (eastern US). These same strata preserve variations in the lake level expression of the climatic precession cycle based on lithology and δD. High cyclicity variance tracked high pCO2 (>~4000 ppm) and drove insolation-paced increases in precipitation. Leaf wax δD shows significant variability, reflecting an enhanced hydrological cycle at the ETE with repeated sudden shifts in relative evaporation for ~1 Myr. In marine strata, 87Sr/86Sr and 187Os/188Os values track changes in pCO2, suggesting a terrestrial/marine linkage through continental weathering, CO2, and runoff. Despite the northward movement of these basins into the arid belt, our data suggest lower evaporation relative to precipitation driven by lower temperatures, consistent with lower pCO2 due to CAMP weathering, which modeling estimates to have increased 6 to 10-fold for >1.6 Myr after the eruptive phase. Release of CO2 from the Karoo-Ferrar LIP similarly enhanced the hydrological cycle as evidenced from sedimentary observations (e.g., fine-scale turbidites and debris flow deposits) in Yorkshire (UK). The onset of the carbon isotope excursion at the T-OAE lasts 0.5 Myr with a 1.5 Myr duration modulated by astronomical pacing. Our leaf wax δD from the same strata show a transient enhancement in the hydrological cycle. Although the Karoo-Ferrar has a limited drawdown potential when compared with CAMP‐type basalts because of its higher latitude location, Toarcian weathering rates may have increased 2 to 5-fold, acting as a net sink 1–2 Myr after eruptions ceased.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-18-169-2021
