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1. Reducing CO ₂ emissions by targeting the world’s hyper-polluting power plants ^*

   https://doi.org/10.1088/1748-9326/ac13f1  

   Grant, Don; Zelinka, David; Mitova, Stefania (August 2021, Environmental Research Letters)

   Abstract Combusting fossil fuels to produce electricity is the single largest contributor to sector-level, anthropogenic carbon pollution. Because sector-wide policies are often too unwieldy to implement, however, some researchers have recommended reducing electricity-based CO₂emissions by targeting the most extreme emitters of each nation’s electricity industry. Here, we use a unique international data source to measure national disproportionalities in power plant CO₂emissions and estimate the fraction of each country’s electricity-based CO₂emissions that would be reduced if its most profligate polluters lowered their emission intensities, switched to gas fuels, and incorporated carbon capture and storage systems. We find that countries’ disproportionalities vary greatly and have mostly grown over time. We also find that 17%–49% of the world’s CO₂emissions from electricity generation could be eliminated depending on the intensity standards, fuels, or carbon capture technologies adopted by hyper-emitting plants. This suggests that policies aimed at improving the environmental performance of ‘super polluters’ are effective strategies for transitioning to decarbonized energy systems. 

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2. Provincial-scale assessment of direct air capture to meet China’s climate neutrality goal under limited bioenergy supply

   https://doi.org/10.1088/1748-9326/ad77e7  

   Kim, Hanwoong; Qiu, Yang; McJeon, Haewon; Clarens, Andres; Javadi, Parisa; Wang, Can; Wang, Rui; Wang, Jiachen; Jiang, Hanying; Miller, Andy; et al (October 2024, Environmental Research Letters)

   Abstract China has large, estimated potential for direct air carbon capture and storage (DACCS) but its deployment locations and impacts at the subnational scale remain unclear. This is largely because higher spatial resolution studies on carbon dioxide removal (CDR) in China have focused mainly on bioenergy with carbon capture and storage. This study uses a spatially detailed integrated energy-economy-climate model to evaluate DACCS for 31 provinces in China as the country pursues its goal of climate neutrality by 2060. We find that DACCS could expand China’s negative emissions capacity, particularly under sustainability-minded limits on bioenergy supply that are informed by bottom-up studies. But providing low-carbon electricity for multiple GtCO₂yr⁻¹DACCS may require over 600 GW of additional wind and solar capacity nationwide and comprise up to 30% of electricity demand in China’s northern provinces. Investment requirements for DACCS range from $330 to $530 billion by 2060 but could be repaid manyfold in the form of avoided mitigation costs, which DACCS deployment could reduce by up to $6 trillion over the same period. Enhanced efforts to lower residual CO₂emissions that must be offset with CDR under a net-zero paradigm reduce but do not eliminate the use of DACCS for mitigation. For decision-makers and the energy-economy models guiding them, our results highlight the value of expanding beyond the current reliance on biomass for negative emissions in China. 

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3. Land use strategies to mitigate climate change in carbon dense temperate forests

   https://doi.org/10.1073/pnas.1720064115  

   Law, Beverly E.; Hudiburg, Tara W.; Berner, Logan T.; Kent, Jeffrey J.; Buotte, Polly C.; Harmon, Mark E. (April 2018, Proceedings of the National Academy of Sciences)

   Strategies to mitigate carbon dioxide emissions through forestry activities have been proposed, but ecosystem process-based integration of climate change, enhanced CO 2 , disturbance from fire, and management actions at regional scales are extremely limited. Here, we examine the relative merits of afforestation, reforestation, management changes, and harvest residue bioenergy use in the Pacific Northwest. This region represents some of the highest carbon density forests in the world, which can store carbon in trees for 800 y or more. Oregon’s net ecosystem carbon balance (NECB) was equivalent to 72% of total emissions in 2011–2015. By 2100, simulations show increased net carbon uptake with little change in wildfires. Reforestation, afforestation, lengthened harvest cycles on private lands, and restricting harvest on public lands increase NECB 56% by 2100, with the latter two actions contributing the most. Resultant cobenefits included water availability and biodiversity, primarily from increased forest area, age, and species diversity. Converting 127,000 ha of irrigated grass crops to native forests could decrease irrigation demand by 233 billion m 3 ⋅y −1 . Utilizing harvest residues for bioenergy production instead of leaving them in forests to decompose increased emissions in the short-term (50 y), reducing mitigation effectiveness. Increasing forest carbon on public lands reduced emissions compared with storage in wood products because the residence time is more than twice that of wood products. Hence, temperate forests with high carbon densities and lower vulnerability to mortality have substantial potential for reducing forest sector emissions. Our analysis framework provides a template for assessments in other temperate regions. 

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4. Land-use emissions play a critical role in land-based mitigation for Paris climate targets

   https://doi.org/10.1038/s41467-018-05340-z  

   Harper, Anna B.; Powell, Tom; Cox, Peter M.; House, Joanna; Huntingford, Chris; Lenton, Timothy M.; Sitch, Stephen; Burke, Eleanor; Chadburn, Sarah E.; Collins, William J.; et al (August 2018, Nature Communications)

   Abstract Scenarios that limit global warming to below 2 °C by 2100 assume significant land-use change to support large-scale carbon dioxide (CO₂) removal from the atmosphere by afforestation/reforestation, avoided deforestation, and Biomass Energy with Carbon Capture and Storage (BECCS). The more ambitious mitigation scenarios require even greater land area for mitigation and/or earlier adoption of CO₂removal strategies. Here we show that additional land-use change to meet a 1.5 °C climate change target could result in net losses of carbon from the land. The effectiveness of BECCS strongly depends on several assumptions related to the choice of biomass, the fate of initial above ground biomass, and the fossil-fuel emissions offset in the energy system. Depending on these factors, carbon removed from the atmosphere through BECCS could easily be offset by losses due to land-use change. If BECCS involves replacing high-carbon content ecosystems with crops, then forest-based mitigation could be more efficient for atmospheric CO₂removal than BECCS. 

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5. Global Trends in Air‐Water CO ₂ Exchange Over Seagrass Meadows Revealed by Atmospheric Eddy Covariance

   https://doi.org/10.1029/2020GB006848  

   Van Dam, Bryce; Polsenaere, Pierre; Barreras‐Apodaca, Aylin; Lopes, Christian; Sanchez‐Mejia, Zulia; Tokoro, Tatsuki; Kuwae, Tomohiro; Loza, Lucia Gutiérrez; Rutgersson, Anna; Fourqurean, James; et al (April 2021, Global Biogeochemical Cycles)

   Abstract Coastal vegetated habitats like seagrass meadows can mitigate anthropogenic carbon emissions by sequestering CO₂as “blue carbon” (BC). Already, some coastal ecosystems are actively managed to enhance BC storage, with associated BC stocks included in national greenhouse gas inventories. However, the extent to which BC burial fluxes are enhanced or counteracted by other carbon fluxes, especially air‐water CO₂flux (FCO₂) remains poorly understood. In this study, we synthesized all available direct FCO₂measurements over seagrass meadows made using atmospheric Eddy Covariance, across a globally representative range of ecotypes. Of the four sites with seasonal data coverage, two were net CO₂sources, with average FCO₂equivalent to 44%–115% of the global average BC burial rate. At the remaining sites, net CO₂uptake was 101%–888% of average BC burial. A wavelet coherence analysis demonstrated that FCO₂was most strongly related to physical factors like temperature, wind, and tides. In particular, tidal forcing was a key driver of global‐scale patterns in FCO₂, likely due to a combination of lateral carbon exchange, bottom‐driven turbulence, and pore‐water pumping. Lastly, sea‐surface drag coefficients were always greater than the prediction for the open ocean, supporting a universal enhancement of gas‐transfer in shallow coastal waters. Our study points to the need for a more comprehensive approach to BC assessments, considering not only organic carbon storage, but also air‐water CO₂exchange, and its complex biogeochemical and physical drivers. 

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