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Enhanced weathering is a simple and scalable negative emissions technology with an estimated carbon dioxide removal potential of multiple gigatons per year. To date, the only life-cycle assessment of enhanced weathering was published by Lefebvre et al. (2019) in this journal. They estimated the carbon dioxide removal potential in Sao Paolo State in Brazil to be 1.3–2.4 Mt/y, examined the penalty from transportation greenhouse gas emissions, and pointed out that using life-cycle assessment can give more reliable estimates of climate change mitigation potential of enhanced weathering systems. In this letter, we discuss the limitations of life-cycle assessment of enhanced weathering, and then propose a more comprehensive life-cycle optimization approach, where the system configuration can be automatically synthesized to maximize environmental performance. This concept can be extended further to life-cycle sustainability optimization by including economic and social dimensions. • The first life cycle assessment of enhanced weathering was reported in 2019. • Life cycle optimization and life cycle sustainability assessment are also needed. • A combined life cycle sustainability optimization framework should be developed. • Hybrid models can be used to address future issues in enhanced weathering. [ABSTRACT FROM AUTHOR]

This study aims to provide an Integrated Assessment Model (IAM) perspective of the production and distribution of alternative marine fuels in Brazilian ports, considering the International Maritime Organization (IMO) emission reduction target for 2050 (IMO2050). Although other mitigation measures are available, it is likely that alternative fuels will be required, implying additional costs and entailing relevant impacts on other energy chains and land use. Hence, the national IAM BLUES model is adapted to represent the relevant part of the international shipping sector. A set of scenarios is developed considering different fuel alternatives, demand assumptions and national mitigation targets. Findings show that taking into account emissions of CO 2 only or of all greenhouse gases (GHGs) within the IMO strategy significantly impacts the optimal technological portfolio. Furthermore, achieving the IMO2050 goal without considering a national decarbonization strategy may result in potential spillovers. The intense use of the energy sector could partially compromise the gains obtained by maritime decarbonization or even surpass it. Therefore, only an integrated mitigation strategy would lead to more effective decarbonization of the entire marine supply. • There is no single optimal portfolio of alternative fuels for shipping. • Brazil can fulfil any low-carbon marine fuel strategy. • Marine fuels should be part of all national decarbonization strategies. • The decarbonization of shipping should be part of Brazil's deep mitigation pathways. [ABSTRACT FROM AUTHOR]

• This sugarcane agro-system was a carbon sink. • The NEE of CO 2 fluxes (assimilation versus respiration) dominated the balances. • The N 2 O and CH 4 emitted totals were offset by the C gain. The sustainability of sugarcane farming for biofuel has recently become a subject of debate, because its expansion may contribute significantly to global climate change mitigation. Here we report greenhouse gases (GHG) fluxes, measured by the eddy covariance method, from a commercial scale rain-fed sugarcane plantation representative of the leading bioethanol production area in southeast Brazil. The measurements covered two harvests, during which the field received nitrogen fertilization and trash was not removed. The cumulative fluxes for nitrous oxide (N 2 O) (62.4 ± 1.3 and 52.3 ± 1.8 g N 2 O CO 2 eq. m−2 for the first and second years, respectively) and methane (CH 4) (12.1 ± 1.7 and 10.4 ± 2.3 g CH 4 CO 2 eq. m−2 for the first and second years, respectively) were minor sources to the atmosphere in comparison with the net ecosystem exchange (NEE) of carbon dioxide (CO 2), whose sink dominated the balances (−7643. ± 129. and -4615. ± 124. g CO 2 m−2 for the first and second years, respectively). Compared to the first year, the observed NEE in the second year decreased by 40%, as it covered the first re-growth from the stubble (ratoon) and exhibited a shorter growth cycle than the first year (304 versus 390 days). The second year also included the partial decomposition of the trash remaining on the soil after the first harvest (1581 ± 301 g CO 2 m−2). The net ecosystem carbon balances (NECB), obtained as the cumulative fluxes of GHGs and the stalk dry biomass removed in the harvests (4923 ± 459 and 3929 ± 352 g CO 2 m−2 for the first and second years, respectively) were -2646 ± 459 and -623 ± 352 g CO 2 m−2 for the first and second years, respectively. Although the yields in stalk fresh weight (SFW) were representative of the region (9.9 and 8.2 kg SFW m−2, in the first and second year respectively) other factors caused a decrease of 76% in NECB, stressing the importance of the CO 2 balance (assimilation versus respiration). Nevertheless, this sugarcane agro-system was an overall carbon sink with the N 2 O and CH 4 emitted totals being offset by the net carbon gain. Image, graphical abstract [ABSTRACT FROM AUTHOR]