Atmospheric Carbon

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    Comprehensive evidence implies a higher social cost of CO2
    (Springer Nature, 2022-09-01) Rennert, Kevin; Errickson, Frank; Prest, Brian C.; Rennels, Lisa; Newell, Richard G.; Pizer, William; Kingdon, Cora; Wingenroth, Jordan; Cooke, Roger; Parthum, Bryan; Smith, David; Cromar, Kevin; Diaz, Delavane; Moore, Frances C.; Müller, Ulrich K.; Plevin, Richard J.; Raftery, Adrian E.; Ševčíková, Hana; Sheets, Hannah; Stock, James H.; Tan, Tammy; Watson, Mark; Wong, Tony E.; Anthoff, David
    The social cost of carbon dioxide (SC-CO2) measures the monetized value of the damages to society caused by an incremental metric tonne of CO2 emissions and is a key metric informing climate policy. Used by governments and other decision-makers in benefit–cost analysis for over a decade, SC-CO2 estimates draw on climate science, economics, demography and other disciplines. However, a 2017 report by the US National Academies of Sciences, Engineering, and Medicine (NASEM) highlighted that current SC-CO2 estimates no longer reflect the latest research. The report provided a series of recommendations for improving the scientific basis, transparency and uncertainty characterization of SC-CO2 estimates. Here we show that improved probabilistic socioeconomic projections, climate models, damage functions, and discounting methods that collectively reflect theoretically consistent valuation of risk, substantially increase estimates of the SC-CO2. Our preferred mean SC-CO2 estimate is $185 per tonne of CO2 ($44–$413 per tCO2: 5%–95% range, 2020 US dollars) at a near-term risk-free discount rate of 2%, a value 3.6 times higher than the US government’s current value of $51 per tCO2. Our estimates incorporate updated scientific understanding throughout all components of SC-CO2 estimation in the new open-source Greenhouse Gas Impact Value Estimator (GIVE) model, in a manner fully responsive to the near-term NASEM recommendations. Our higher SC-CO2 values, compared with estimates currently used in policy evaluation, substantially increase the estimated benefits of greenhouse gas mitigation and thereby increase the expected net benefits of more stringent climate policies.
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    The impact of human and livestock respiration on CO2 emissions from 14 global cities
    (Springer Nature, 2022-11-03) Cai, Qixiang; Zeng, Ning; Zhao, Fang; Han, Pengfei; Liu, Xiaohui; Chen, Jingwen
    Background: The CO2 released by humans and livestock through digestion and decomposition is an important part of the urban carbon cycle, but is rarely considered in studies of city carbon budgets since its annual magnitude is usually much lower than that of fossil fuel emissions within the boundaries of cities. However, human and livestock respiration may be substantial compared to fossil fuel emissions in areas with high population density such as Manhattan or Beijing. High-resolution datasets of CO2 released from respiration also have rarely been reported on a global scale or in cities globally. Here, we estimate the CO2 released by human and livestock respiration at global and city scales and then compare it with the carbon emissions inventory from fossil fuels in 14 cities worldwide. Results: The results show that the total magnitude of human and livestock respiration emissions is 38.2% of the fossil fuel emissions in Sao Paulo, highest amongst the 14 cities considered here. The proportion is larger than 10% in cities of Delhi, Cape Town and Tokyo. In other cities, it is relatively small with a proportion around 5%. In addition, almost 90% of respiratory carbon comes from urban areas in most of the cities, while up to one-third comes from suburban areas in Beijing on account of the siginificant livestock production. Conclusion: The results suggest that the respiration of human and livestock represents a significant CO2 source in some cities and is nonnegligible for city carbon budget analysis and carbon monitoring.
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    On the use of Earth Observation to support estimates of national greenhouse gas emissions and sinks for the Global stocktake process: lessons learned from ESA-CCI RECCAP2
    (Springer Nature, 2022-10-01) Bastos, Ana; Ciais, Phillippe; Sitch, Stephen; Aragão, Luiz O. C.; Chevallier, Frédéric; Fawcett, Dominic; Rosan, Thais M.; Saunois, Marielle; Günther, Dirk; Perugini, Lucia; Robert, Colas; Deng, Zhu; Pongratz, Julia; Ganzenmüller, Raphael; Fuchs, Richard; Winkler, Karina; Zaehle, Sönke; Albergel, Clément
    The Global Stocktake (GST), implemented by the Paris Agreement, requires rapid developments in the capabilities to quantify annual greenhouse gas (GHG) emissions and removals consistently from the global to the national scale and improvements to national GHG inventories. In particular, new capabilities are needed for accurate attribution of sources and sinks and their trends to natural and anthropogenic processes. On the one hand, this is still a major challenge as national GHG inventories follow globally harmonized methodologies based on the guidelines established by the Intergovernmental Panel on Climate Change, but these can be implemented diferently for individual countries. Moreover, in many countries the capability to systematically produce detailed and annually updated GHG inventories is still lacking. On the other hand, spatially-explicit datasets quantifying sources and sinks of carbon dioxide, methane and nitrous oxide emissions from Earth Observations (EO) are still limited by many sources of uncertainty. While national GHG inventories follow diverse methodologies depending on the availability of activity data in the diferent countries, the proposed comparison with EO-based estimates can help improve our understanding of the comparability of the estimates published by the diferent countries. Indeed, EO networks and satellite platforms have seen a massive expansion in the past decade, now covering a wide range of essential climate variables and ofering high potential to improve the quantifcation of global and regional GHG budgets and advance process understanding. Yet, there is no EO data that quantifes greenhouse gas fuxes directly, rather there are observations of variables or proxies that can be transformed into fuxes using models. Here, we report results and lessons from the ESA-CCI RECCAP2 project, whose goal was to engage with National Inventory Agencies to improve understanding about the methods used by each community to estimate sources and sinks of GHGs and to evaluate the potential for satellite and in-situ EO to improve national GHG estimates. Based on this dialogue and recent studies, we discuss the potential of EO approaches to provide estimates of GHG budgets that can be compared with those of national GHG invento ries. We outline a roadmap for implementation of an EO carbon-monitoring program that can contribute to the Paris Agreement.