Natural climate solutions for the United States

Retention forestry as a climate solution: Assessing biomass, soil carbon and albedo impacts in a northern temperate coniferous forest

Forest management pathways for nature-based climate solutions, such as variable retention harvesting (VRH), have been gaining traction in recent years; however, their net biochemical and biophysical impacts remain unknown. Here, we use a combination of close-range and satellite remote sensing, eddy covariance technique, and ground-based biometric measurements to investigate forest thinning density and aggregation that maintain ecosystem nutrients, enhance tree growth and provide a negative feedback to the local climate in a northern temperate coniferous forest stand in Ontario, Canada. Our results showed that soil carbon (C) and nitrogen (N) in VRH plots were significantly lower (p < 0.05) for all VRH treatments compared to unharvested plots. On average, soil C was reduced by -0.64 ± 0.22 Δ% C and N by -0.023 ± 0.008 Δ% N in VRH plots. We also observed the largest loss of soil C and N in open areas of aggregate plots. Furthermore, the changes in albedo resulting from VRH treatment were equivalent to removing a large amount of C from the atmosphere, ranging from 1.3 ± 0.2 kg C yr-1 m-2 in aggregate 33 % crown retention plots to 3.4 ± 0.5 kg C yr-1 m-2 in dispersed 33 % crown retention plots. Our findings indicate that spatially dispersed VRH resulted in minimal loss of soil C and N and the highest understory growth and C uptake, while enhanced tree growth and local cooling through increased albedo were observed in dispersed VRH plots with the fewest residual trees. These findings suggest that using the harvested trees from VRH in a way that avoids releasing C into the atmosphere makes dispersed VRH the preferred forest management pathway for nature-based climate solutions.

The potential climate benefits of seaweed farming in temperate waters

Seaweed farming is widely promoted as an approach to mitigating climate change despite limited data on carbon removal pathways and uncertainty around benefits and risks at operational scales. We explored the feasibility of climate change mitigation from seaweed farming by constructing five scenarios spanning a range of industry development in coastal British Columbia, Canada, a temperate region identified as highly suitable for seaweed farming. Depending on growth rates and the fate of farmed seaweed, our scenarios sequestered or avoided between 0.20 and 8.2 Tg CO2e year-1, equivalent to 0.3% and 13% of annual greenhouse gas emissions in BC, respectively. Realisation of climate benefits required seaweed-based products to replace existing, more emissions-intensive products, as marine sequestration was relatively inefficient. Such products were also key to reducing the monetary cost of climate benefits, with product values exceeding production costs in only one of the scenarios we examined. However, model estimates have large uncertainties dominated by seaweed production and emissions avoided, making these key priorities for future research. Our results show that seaweed farming could make an economically feasible contribute to Canada's climate goals if markets for value-added seaweed based products are developed. Moreover, our model demonstrates the possibility for farmers, regulators, and researchers to accurately quantify the climate benefits of seaweed farming in their regional contexts.

Climate mitigation potential of cover crops in the United States is regionally concentrated and lower than previous estimates

Widespread adoption of regenerative agriculture practices is an integral part of the US plan to achieve net-zero greenhouse gas emissions by 2050. National incentives have particularly increased for the adoption of cover crops (CCs), which have presumably large carbon (C) sequestration potential. However, assessments of national CC climate benefits have not fully considered regional variability, changing C sequestration rates over time, and potential N2O trade-offs. Using the DayCent soil biogeochemical model and current national survey data, we estimate CC climate change mitigation potential to be 39.0 ± 24.1 Mt CO2e year-1, which is 45%-65% lower than previous estimates, with large uncertainty attributed to N2O impacts. Three-fourths of this climate change mitigation potential is concentrated in the North Central, Southern Great Plains and Lower Mississippi regions. Public investment should be focused in these regions to maximize CC climate benefits, but the national contribution of CC to emissions targets may be lower than previously anticipated.

Merging adoption of natural climate solutions in agriculture with climatic and non-climatic risks within an (intra)gendered framework

The extant research on climate variability shares significant theoretical contributions to vulnerability and risks. However, the literature mostly focuses on technical solutions to climate extremes which undermines efforts to identify and solve the dynamics within gender groups in using agricultural-based natural climate solutions (NCS) to address climatic and non-climatic risks. With this in mind, this study implements both quantitative and qualitative approaches including household surveys, key informant interviews, and focus group discussions to investigate the adoption of NCS within gender groups to address climatic and non-climatic risks in three selected communities (Katanga, Dakio, and Zonno) in the Bolgatanga East District of Upper East Region of Ghana. The Relative Importance Index (RII) was used to rank the key climatic and non-climatic risks confronting smallholder farmers in the district. Male and female smallholder farmers affirmed that there has been variation in the climate compared to their childhood. The results indicated climate change-induced erosion (RII = 0.268) as the highest climatic risk among male smallholder farmers. Increased bushfire (RII = 0.263) was the highest climatic risk affecting female smallholder farmers. The findings show that the high cost of farm inputs (RII = 0.505) is the highest non-climatic risk among the male smallholder farmers whereas inadequate credit facilities (RII = 0.295) affected most of the female smallholder farmers. In adapting to the climatic risks, both male and female smallholder farmers with no formal education plant early maturing crop varieties and cover crops on their farmland. Others engage in traditional non-farm activities such as weaving by using renewable materials with reduced ecological footprints to address non-climatic risks. The male and female smallholder farmers with post-secondary education typically resort to temporal migration during the dry season to work on non-farm jobs. Acknowledging the intra-gendered adoption of NCS among marginalized farming households; not only protects against maladaptation but also improves local-level resilience and climate risk management in Ghana.

Site properties, environmental factors, and crop identify influence soil bacterial communities more than municipal biosolid application

Reducing the environmental impact of Canadian field crop agriculture, including the reliance on conventional synthesised fertilisers, are key societal targets for establishing long-term sustainable practices. Municipal biosolids (MSB) are an abundant, residual organic material, rich in phosphate, nitrogen and other oligo-nutrients, that could be used in conjunction with conventional fertilisers to decrease their use. Though MBS have previously been shown to be an effective fertiliser substitute for different crops, including corn and soybean, there remain key knowledge gaps concerning the impact of MBS on the resident soil bacterial communities in agro-ecosystems. We hypothesised that the MBS fertiliser amendment would not significantly impact the structure or function of the soil bacterial communities, nor contribute to the spread of human pathogenic bacteria, in corn or soybean agricultural systems. In field experiments, fertiliser regimes for both crops were amended with MBS, and compared to corn and soybean plots with standard fertiliser treatments. We repeated this across four different agricultural sites in Quebec, over 2021 and 2022. We sampled MBS-treated, and untreated soils, and identified the composition of the soil bacterial communities via 16S rRNA metabarcoding. We found no indication that the MBS fertiliser amendment altered the structure of the soil bacterial communities, but rather that the soil type and crop identities were the most significant factors in structuring the bacterial communities. Moreover, there was no evidence that the MBS-treated soils were enriched in potential human bacterial pathogens over the two years of our study. Our analysis indicates that not only can MBS function as substitutes for conventional, synthesised fertilisers, but that they also do not disrupt the structure of the resident soil bacterial communities in the short term. Finally, we suggest that the use of MBS in agro-ecosystems poses no greater concern to the public than existing soil bacterial communities. This highlights the significant role MBS could potentially have in reducing the use of conventional industrial fertilisers and improving agricultural production, without risking environmental contamination.

A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

Accounting for albedo change to identify climate-positive tree cover restoration

Restoring tree cover changes albedo, which is the fraction of sunlight reflected from the Earth's surface. In most locations, these changes in albedo offset or even negate the carbon removal benefits with the latter leading to global warming. Previous efforts to quantify the global climate mitigation benefit of restoring tree cover have not accounted robustly for albedo given a lack of spatially explicit data. Here we produce maps that show that carbon-only estimates may be up to 81% too high. While dryland and boreal settings have especially severe albedo offsets, it is possible to find places that provide net-positive climate mitigation benefits in all biomes. We further find that on-the-ground projects are concentrated in these more climate-positive locations, but that the majority still face at least a 20% albedo offset. Thus, strategically deploying restoration of tree cover for maximum climate benefit requires accounting for albedo change and we provide the tools to do so.

The inclusion of Amazon mangroves in Brazil's REDD+ program

The Legal Amazon of Brazil holds vast mangrove forests, but a lack of awareness of their value has prevented their inclusion into results-based payments established by the United Nations Framework Convention on Climate Change. Based on an inventory from over 190 forest plots in Amazon mangroves, we estimate total ecosystem carbon stocks of 468 ± 67 Megagrams (Mg) ha-1; which are significantly higher than Brazilian upland biomes currently included into national carbon offset financing. Conversion of mangroves results in potential emissions of 1228 Mg CO2e ha-1, which are 3-fold higher than land use emissions from conversion of the Amazon rainforest. Our work provides the foundation for the inclusion of mangroves in Brazil's intended Nationally Determined Contribution, and here we show that halting mangrove deforestation in the Legal Amazon would generate avoided emissions of 0.9 ± 0.3 Teragrams (Tg) CO2e yr-1; which is equivalent to the annual carbon accumulation in 82,400 ha of secondary forests.

Harnessing weedy rice as functional food and source of novel traits for crop improvement

A relative of cultivated rice (Oryza sativa L.), weedy or red rice (Oryza spp.) is currently recognized as the dominant weed, leading to a drastic loss of yield of cultivated rice due to its highly competitive abilities like producing more tillers, panicles, and biomass with better nutrient uptake. Due to its high nutritional value, antioxidant properties (anthocyanin and proanthocyanin), and nutrient absorption ability, weedy rice is gaining immense research attentions to understand its genetic constitution to augment future breeding strategies and to develop nutrition-rich functional foods. Consequently, this review focuses on the unique gene source of weedy rice to enhance the cultivated rice for its crucial features like water use efficiency, abiotic and biotic stress tolerance, early flowering, and the red pericarp of the seed. It explores the debating issues on the origin and evolution of weedy rice, including its high diversity, signalling aspects, quantitative trait loci (QTL) mapping under stress conditions, the intricacy of the mechanism in the expression of the gene flow, and ecological challenges of nutrient removal by weedy rice. This review may create a foundation for future researchers to understand the gene flow between cultivated crops and weedy traits and support an improved approach for the applicability of several models in predicting multiomics variables.

Modeling wood product carbon flows in southern us pine plantations: implications for carbon storage

BACKGROUND

Wood products continue to store carbon sequestered in forests after harvest and therefore play an important role in the total carbon storage associated with the forest sector. Trade-offs between carbon sequestration/storage in wood product pools and managed forest systems exist, and in order for forest sector carbon modeling to be meaningful, it must link wood product carbon with the specific forest system from which the products originate and have the ability to incorporate in situ and ex situ carbon synchronously over time.

RESULTS

This study uses elements of a life cycle assessment approach, tracing carbon from US southern pine timber harvests to emission, to create a decision support tool that practitioners can use to inform policy design around land- and bioproduct-based mitigation strategies. We estimate that wood products from annual loblolly and shortleaf pine timber harvests across the southern US store 29.7 MtC in the year they enter the market, and 11.4 MtC remain stored after 120 years. We estimate fossil fuel emissions from the procurement, transportation, and manufacturing of these wood products to be 43.3 MtCO2e year-1. We found that composite logs, used to manufacture oriented strand board (OSB), were the most efficient log type for storing carbon, storing around 1.8 times as much carbon as saw logs per tonne of log over 120 years.

CONCLUSIONS

Results from our analysis suggest that adjusting rotation length based on individual site productivity, reducing methane emissions from landfills, and extending the storage of carbon in key products, such as corrugated boxes, through longer lifespans, higher recycling rates, and less landfill decomposition could result in significant carbon gains. Our results also highlight the benefits of high site productivity to store more carbon in both in situ and ex situ pools and suggest that shorter rotations could be used to optimize carbon storage on sites when productivity is high.

The principles of natural climate solutions

Natural climate solutions can mitigate climate change in the near-term, during a climate-critical window. Yet, persistent misunderstandings about what constitutes a natural climate solution generate unnecessary confusion and controversy, thereby delaying critical mitigation action. Based on a review of scientific literature and best practices, we distill five foundational principles of natural climate solutions (nature-based, sustainable, climate-additional, measurable, and equitable) and fifteen operational principles for practical implementation. By adhering to these principles, practitioners can activate effective and durable natural climate solutions, enabling the rapid and wide-scale adoption necessary to meaningfully contribute to climate change mitigation.

Knowledge-guided machine learning can improve carbon cycle quantification in agroecosystems

Accurate and cost-effective quantification of the carbon cycle for agroecosystems at decision-relevant scales is critical to mitigating climate change and ensuring sustainable food production. However, conventional process-based or data-driven modeling approaches alone have large prediction uncertainties due to the complex biogeochemical processes to model and the lack of observations to constrain many key state and flux variables. Here we propose a Knowledge-Guided Machine Learning (KGML) framework that addresses the above challenges by integrating knowledge embedded in a process-based model, high-resolution remote sensing observations, and machine learning (ML) techniques. Using the U.S. Corn Belt as a testbed, we demonstrate that KGML can outperform conventional process-based and black-box ML models in quantifying carbon cycle dynamics. Our high-resolution approach quantitatively reveals 86% more spatial detail of soil organic carbon changes than conventional coarse-resolution approaches. Moreover, we outline a protocol for improving KGML via various paths, which can be generalized to develop hybrid models to better predict complex earth system dynamics.

Exploring carbon sequestration in broad-leaved Korean pine forests: Insights into photosynthetic and respiratory processes

A comprehensive understanding of carbon assimilation and sequestration in broad-leaved Korean pine forests is crucial for accurately estimating this significant aspect of temperate forests at a regional scale. In this study, we introduced a high-temporal resolution model designed for carbon assimilation insights at the plot scale, focusing on specific parameters such as leaf area dynamics, vertical leaf distribution, photosynthetically active radiation (PAR) fluctuations, and the photosynthetic traits of tree species. The findings reveal that most tree species in broad-leaved Korean pine forests exhibit an inverted U-shaped pattern in leaf area dynamics, with shorter leaf drop periods than leaf expansion events. Leaf distribution varies significantly among different canopy heights, with approximately 80 % of the leaves above 15 m. PAR decreases as canopy height decreases, with PAR at 25 m accounting for about 60 % of the PAR above the canopy. Our framework incorporates a leaf-scale light-response curve and empirical photosynthesis-temperature relationships to estimate forest carbon assimilation on daily and hourly scales accurately. Using the model, we assess the gross primary productivity (GPP), leaf net photosynthetic assimilation (LNPA), and carbon increment (ΔC) of broad-leaved Korean pine forests from 2017 to 2020. The results demonstrate GPP, LNPA, and ΔC values of 21.4 t·ha-1·a-1, 17.4 t·ha-1·a-1, and 4.0 t·ha-1·a-1, respectively. Regarding efficiency, GPP, LNPA, and ΔC per square meter of leaf per year are 179 g, 146 g, and 33 g, respectively. Notably, tree species in the canopy layer of the forest exhibit significantly higher efficiency than those in the understory layer. This research significantly contributes to our understanding of carbon cycling and the responses of forest ecosystems to climate change. Moreover, it provides a practical tool for forest management and the development of carbon sequestration strategies.

Influence of rice-wheat and sugarcane-wheat rotations on microbial diversity and plant growth promoting bacteria: Insights from high-throughput sequencing and soil analysis

Wheat is a staple food crop, primarily grown in India's Indo-Gangetic plains, crucial for sustaining the region. Soil quality, vitality, and microbial inhabitants' interplay are pivotal. However, very little information is available on the impacts of agricultural practices, such as crop rotation and cropping systems, on the diversity of both bulk soil (BS) and rhizospheric soil (RS) microbiota. The impact of two different cropping systems, rice-wheat (RW) and sugarcane-wheat (SW) on soil properties, microbial diversity, and plant growth-promoting bacteria (PGPB) in wheat cultivation was investigated in the Indo-Gangetic plains of India. Microbial richness and diversity were analyzed using 16S rRNA sequencing, which reveals distinct clustering patterns between RS and BS, with higher diversity in BS of RW and higher richness in RS of SW. Notably, Proteobacteria dominated across all samples, along with Chloroflexi, Actinobacteria, Bacteroidetes, Acidobacteria, Gemmatimonadetes, Verrucomicrobia, Firmicutes, Planctomycetes, candidate division TM7, Cyanobacteria, and Nitrospirae. Intriguingly, the RS associated with the SW system exhibited the presence of 67 distinct genera, whereas the RS under the RW system showed 48 such genera. Within the realm of specific microbial genera exhibiting plant growth-promoting (PGP) activity, a higher abundance was noted in the RS (17.48%), as opposed to the BS (15.21%). Moreover, certain genera such as Haliangium, Iamia, Bacillus, Gaiella, Candidatus_Entotheonella, Anaerolinea, and Anaeromyxobacter, were found to be positively correlated with the availability of nitrogen, phosphorus, potassium, iron, and sulfur. The study sheds light on the intricate relationships between cropping practices, soil properties, and microbial dynamics, contributing to the development of sustainable agricultural practices for wheat cultivation.

The pandemic effect on GHG emission variation at the sub-national level and translation into policy opportunities

Greenhouse gas (GHG) emissions inventories are commonly compiled at country level to monitor national progress towards nationally or internationally agreed targets. While they can support national climate change mitigation strategies, accounting for the intra-national heterogeneity of a country can draw different conclusions directly linked to the socio-economic and environmental sub-national context. This means that more refined and accurate policies and mitigation strategies can be designed when supported by GHG inventories at sub-national scale. The differences between sub-national territorial emissive behavior can be revealed by subjecting different territories to the same stress factors. A complete GHG emissions inventory, based on the Intergovernmental Panel on Climate Change (IPCC) Guidelines, is compiled for three diverse administrative territories, in terms of scale, socio-economic contexts, and environmental conditions. By selecting three diverse sub-national contexts belonging to the same national territory - Italy - the analysis provides highly detailed information on the emissive status and behavior and delivers insights that national inventories fail to provide. The COVID-19 pandemic is considered as a stress factor; therefore, the reference years are 2019 and 2020 during which GHG emissions are detected. The study will test the capacity of sub-national GHG emission inventories, compiled by scaling the IPCC methodology to the sub-national level, to detect such differences through the lens of the pandemic. This allows obtaining detailed information and linking the pandemic effect to the GHG emissions of particular activities, which can inspire effective sub-national context-specific mitigation actions. Furthermore, we show that environmental and economic metrics are not as strictly coupled as they would appear at national level.

Net greenhouse gas balance in U.S. croplands: How can soils be part of the climate solution?

Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO2 ) in soil organic carbon (SOC) and emitting non-CO2 greenhouse gases (GHGs) such as nitrous oxide (N2 O) and methane (CH4 ). To understand how agricultural soils can play a role in climate solutions requires a comprehensive assessment of net soil GHG balance (i.e., sum of SOC-sequestered CO2 and non-CO2 GHG emissions) and the underlying controls. Herein, we used a model-data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960-2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC sequestration rates and N2 O and CH4 emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered13.2 ± 1.16 $$ 13.2\pm 1.16 $$ Tg CO2 -C year-1 in SOC (at a depth of 3.5 m) during 1960-2018 and emitted0.39 ± 0.02 $$ 0.39\pm 0.02 $$ Tg N2 O-N year-1 and0.21 ± 0.01 $$ 0.21\pm 0.01 $$ Tg CH4 -C year-1 , respectively. Based on the GWP100 metric (global warming potential on a 100-year time horizon), the estimated national net GHG emission rate from agricultural soils was122.3 ± 11.46 $$ 122.3\pm 11.46 $$ Tg CO2 -eq year-1 , with the largest contribution from N2 O emissions. The sequestered SOC offset ~28% of the climate-warming effects resulting from non-CO2 GHG emissions, and this offsetting effect increased over time. Increased nitrogen fertilizer use was the dominant factor contributing to the increase in net GHG emissions during 1960-2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO2 levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N2 O emissions represents the biggest opportunity for achieving net-zero emissions in U.S. croplands. Our study highlights the importance of concurrently quantifying SOC-sequestered CO2 and non-CO2 GHG emissions for developing effective agricultural climate change mitigation measures.

The Structure-Function Relationship of Branched Polyethylenimine Impregnated over Mesoporous Carbon Aerogels: An In-Depth Thermogravimetric Insight

We present a comprehensive thermogravimetric analysis (TGA) of polyethylenimine (PEI)-impregnated resorcinol-formaldehyde (RF) aerogels. While numerous studies focus on PEI-impregnated SBA, RF materials have been less examined, despite their interest and specificities. As most articles on PEI-impregnated porous materials follow typical experimental methods defined for SBA, particularities of RF-PEI materials could remain unheeded. The design of nonisothermal TGA protocols, completed with nitrogen isotherms, based on the systematic filling of the matrix delivers a fundamental understanding of the relationship between the structure and function. This study demonstrates (i) the competition between the matrix and PEI for CO2-physisorption (φ) and CO2-chemisorption (χ), (ii) the hysteresis ([Formula: see text]) of CO2 capture at low temperature attributed to the kinetic (K) hindrance of CO2 diffusion (D) through PEI film/plugs limiting the chemisorption, and (iii) the thermodynamic (θ) equilibrium limiting the capture at high temperature. At variance with SBA-PEI materials, the first layers of PEI in RF are readily available for CO2 capture given that this matrix does not covalently bind PEI as SBA. A facile method allows the discrimination between physi- and chemisorption, exhibiting how the former decreases with PEI coverage. The CO2 capture hysteresis, while seldom introduced or discussed, underlines that the commonly accepted operating temperature of the "maximum capture" is based on an incomplete experiment. Through isotherm adsorption analysis, we correlate the evolution of this maximum to the morphological distribution of PEI. This contribution highlights the specificities of RF-PEI and the advantages of our TGA protocol in understanding the structure/function relationship of this kind of material by avoiding the typical direct applications of SBA-specific protocols. The method is straightforward, does not need large-scale facilities, and is applicable to other materials. Its easiness and rapidness are suited to high-volume studies, befitting for the comprehensive evaluation of interacting factors such as the matrix's nature, pore size, and PEI weight.

Improved net carbon budgets in the US Midwest through direct measured impacts of enhanced weathering

Terrestrial enhanced weathering (EW) through the application of Mg- or Ca-rich rock dust to soil is a negative emission technology with the potential to address impacts of climate change. The effectiveness of EW was tested over 4 years by spreading ground basalt (50 t ha-1  year-1 ) on maize/soybean and miscanthus cropping systems in the Midwest US. The major elements of the carbon budget were quantified through measurements of eddy covariance, soil carbon flux, and biomass. The movement of Mg and Ca to deep soil, released by weathering, balanced by a corresponding alkalinity flux, was used to measure the drawdown of CO2 , where the release of cations from basalt was measured as the ratio of rare earth elements to base cations in the applied rock dust and in the surface soil. Basalt application stimulated peak biomass and net primary production in both cropping systems and caused a small but significant stimulation of soil respiration. Net ecosystem carbon balance (NECB) was strongly negative for maize/soybean (-199 to -453 g C m-2  year-1 ) indicating this system was losing carbon to the atmosphere. Average EW (102 g C m-2  year-1 ) offset carbon loss in the maize/soybean by 23%-42%. NECB of miscanthus was positive (63-129 g C m-2  year-1 ), indicating carbon gain in the system, and EW greatly increased inorganic carbon storage by an additional 234 g C m-2  year-1 . Our analysis indicates a co-deployment of a perennial biofuel crop (miscanthus) with EW leads to major wins-increased harvested yields of 29%-42% with additional carbon dioxide removal (CDR) of 8.6 t CO2  ha-1  year-1 . EW applied to maize/soybean drives a CDR of 3.7 t CO2  ha-1  year-1 , which partially offsets well-established carbon losses from soil from this crop rotation. EW applied in the US Midwest creates measurable improvements to the carbon budgets perennial bioenergy crops and conventional row crops.

Natural climate solutions provide robust carbon mitigation capacity under future climate change scenarios

Natural climate solutions (NCS) are recognized as an important tool for governments to reduce greenhouse gas emissions and remove atmospheric carbon dioxide. Using California as a globally relevant reference, we evaluate the magnitude of biological climate mitigation potential from NCS starting in 2020 under four climate change scenarios. By mid-century NCS implementation leads to a large increase in net carbon stored, flipping the state from a net source to a net sink in two scenarios. Forest and conservation land management strategies make up 85% of all NCS emissions reductions by 2050, with agricultural strategies accounting for the remaining 15%. The most severe climate change impacts on ecosystem carbon materialize in the latter half of the century with three scenarios resulting in California ecosystems becoming a net source of carbon emissions under a baseline trajectory. However, NCS provide a strong attenuating effect, reducing land carbon emissions 41-54% by 2100 with total costs of deployment of 752-777 million USD annually through 2050. Rapid implementation of a portfolio of NCS interventions provides long-term investment in protecting ecosystem carbon in the face of climate change driven disturbances. This open-source, spatially-explicit framework can help evaluate risks to NCS carbon storage stability, implementation costs, and overall mitigation potential for NCS at jurisdictional scales.

Proposed solutions to anthropogenic climate change: A systematic literature review and a new way forward

Humanity is now facing what may be the biggest challenge to its existence: irreversible climate change brought about by human activity. Our planet is in a state of emergency, and we only have a short window of time (7-8 years) to enact meaningful change. The goal of this systematic literature review is to summarize the peer-reviewed literature on proposed solutions to climate change in the last 20 years (2002-2022), and to propose a framework for a unified approach to solving this climate change crisis. Solutions reviewed include a transition toward use of renewable energy resources, reduced energy consumption, rethinking the global transport sector, and nature-based solutions. This review highlights one of the most important but overlooked pieces in the puzzle of solving the climate change problem - the gradual shift to a plant-based diet and global phaseout of factory (industrialized animal) farming, the most damaging and prolific form of animal agriculture. The gradual global phaseout of industrialized animal farming can be achieved by increasingly replacing animal meat and other animal products with plant-based products, ending government subsidies for animal-based meat, dairy, and eggs, and initiating taxes on such products. Failure to act will ultimately result in a scenario of irreversible climate change with widespread famine and disease, global devastation, climate refugees, and warfare. We therefore suggest an "All Life" approach, invoking the interconnectedness of all life forms on our planet. The logistics for achieving this include a global standardization of Environmental, Social, and Governance (ESG) or similar measures and the introduction of a regulatory body for verification of such measures. These approaches will help deliver environmental and sustainability benefits for our planet far beyond an immediate reduction in global warming.

Overlapping neurological phenotypes in two extended consanguineous families with novel variants in the CNTNAP1 and ADGRG1 genes

BACKGROUND

Population diversity is important and rare disease isolates can frequently reveal novel homozygous or biallelic mutations that lead to expanded clinical heterogeneity, with diverse clinical presentations.

METHODS

The present study describes two consanguineous families with a total of seven affected individuals suffering from a clinically similar severe syndromic neurological disorder, with abnormal development and central nervous system (CNS) and peripheral nervous system (PNS) abnormalities. Whole exome sequencing (WES) and Sanger sequencing followed by 3D protein modeling was performed to identify the disease-causing gene. RNA was extracted from the fresh blood of both families affected and healthy individuals.

RESULTS

The families were clinically assessed in the field in different regions of Khyber Pakhtunkhwa. Magnetic resonance imagining was obtained in the probands and blood was collected for DNA extraction and WES was performed. Sanger sequencing confirmed a homozygous, likely pathogenic mutation (GRCh38: chr17:42684199G>C; (NM_003632.3): c.333G>C);(NP_003623.1): p.(Trp111Cys) in the CNTNAP1 gene in family A, previously associated with Congenital Hypo myelinating Neuropathy 3 (CHN3; OMIM # 618186) and a novel nonsense variant in family B, (GRCh38: chr16: 57654086C>T; NC_000016.10 (NM_001370440.1): c.721C>T); (NP_001357369.1): p.(Gln241Ter) in the ADGRG1 gene previously associated with bilateral frontoparietal polymicrogyria (OMIM # 606854); both families have extended CNS and PNS clinical manifestations. In addition, 3D protein modeling was performed for the missense variant, p.(Trp111Cys), identified in the CNTNAP1, suggesting extensive secondary structure changes that might lead to improper function or downstream signaling. No RNA expression was observed in both families affected and healthy individuals hence showing that these genes are not expressed in blood.

CONCLUSIONS

In the present study, two novel biallelic variants in the CNTNAP1 and ADGRG1 genes in two different consanguineous families with a clinical overlap in the phenotype were identified. Thus, the clinical and mutation spectrum is expanded to provide further evidence that CNTNAP1 and ADGRG1 are very important for widespread neurological development.

The neglected role of abandoned cropland in supporting both food security and climate change mitigation

Despite the looming land scarcity for agriculture, cropland abandonment is widespread globally. Abandoned cropland can be reused to support food security and climate change mitigation. Here, we investigate the potentials and trade-offs of using global abandoned cropland for recultivation and restoring forests by natural regrowth, with spatially-explicit modelling and scenario analysis. We identify 101 Mha of abandoned cropland between 1992 and 2020, with a capability of concurrently delivering 29 to 363 Peta-calories yr-1 of food production potential and 290 to 1,066 MtCO2 yr-1 of net climate change mitigation potential, depending on land-use suitability and land allocation strategies. We also show that applying spatial prioritization is key to maximizing the achievable potentials of abandoned cropland and demonstrate other possible approaches to further increase these potentials. Our findings offer timely insights into the potentials of abandoned cropland and can inform sustainable land management to buttress food security and climate goals.

Air-Stable Cu(I) Metal-Organic Framework for Hydrogen Storage

Metal-organic frameworks (MOFs) that contain open metal sites have the potential for storing hydrogen (H2) at ambient temperatures. In particular, Cu(I)-based MOFs demonstrate very high isosteric heats of adsorption for hydrogen relative to other reported MOFs with open metal sites. However, most of these Cu(I)-based MOFs are not stable in ambient conditions since the Cu(I) species display sensitivity toward moisture and can rapidly oxidize in air. As a result, researchers have focused on the synthesis of new air-stable Cu(I)-based materials for H2 storage. Here, we have developed a de novo synthetic strategy to generate a robust Cu(I)-based MOF, denoted as NU-2100, using a mixture of Cu/Zn precursors in which zinc acts as a catalyst to transform an intermediate MOF into NU-2100 without getting incorporated into the final MOF structure. NU-2100 is air-stable and displays one of the initial highest isosteric heats of adsorption (32 kJ/mol) with good hydrogen storage capability under ambient conditions (10.4 g/L, 233 K/100 bar to 296 K/5 bar). We further elucidated the H2 storage performance of NU-2100 using a combination of spectroscopic analysis and computational modeling studies. Overall, this new synthetic route may enable the design of additional stable Cu(I)-MOFs for next-generation hydrogen storage adsorbents at ambient temperatures.

Counterfactual scenarios reveal historical impact of cropland management on soil organic carbon stocks in the United States

Natural climate solutions provide opportunities to reduce greenhouse gas emissions and the United States is among a growing number of countries promoting storage of carbon in agricultural soils as part of the climate solution. Historical patterns of soil organic carbon (SOC) stock changes provide context about mitigation potential. Therefore, our objective was to quantify the influence of climate-smart soil practices on SOC stock changes in the top 30 cm of mineral soils for croplands in the United States using the DayCent Ecosystem Model. We estimated that SOC stocks increased annually in US croplands from 1995 to 2015, with the largest increase in 1996 of 16.6 Mt C (95% confidence interval ranging from 6.1 to 28.2 Mt CO2 eq.) and the lowest increase in 2015 of 10.6 Mt C (95% confidence interval ranging from - 1.8 to 22.2 Mt C). Most climate-smart soil practices contributed to increases in SOC stocks except for winter cover crops, which had a negligible impact due to a relatively small area with cover crop adoption. Our study suggests that there is potential for enhancing C sinks in cropland soils of the United States although some of the potential has been realized due to past adoption of climate-smart soil practices.

The Role of Wildfires in the Interplay of Forest Carbon Stocks and Wood Harvest in the Contiguous United States During the 20th Century

Wildfires and land use play a central role in the long-term carbon (C) dynamics of forested ecosystems of the United States. Understanding their linkages with changes in biomass, resource use, and consumption in the context of climate change mitigation is crucial. We reconstruct a long-term C balance of forests in the contiguous U.S. using historical reports, satellite data, and other sources at multiple scales (national scale 1926-2017, regional level 1941-2017) to disentangle the drivers of biomass C stock change. The balance includes removals of forest biomass by fire, by extraction of woody biomass, by forest grazing, and by biomass stock change, their sum representing the net ecosystem productivity (NEP). Nationally, the total forest NEP increased for most of the 20th century, while fire, harvest and grazing reduced total forest stocks on average by 14%, 51%, and 6%, respectively, resulting in a net increase in C stock density of nearly 40%. Recovery from past land-use, plus reductions in wildfires and forest grazing coincide with consistent forest regrowth in the eastern U.S. but associated C stock increases were offset by increased wood harvest. C stock changes across the western U.S. fluctuated, with fire, harvest, and other disturbances (e.g., insects, droughts) reducing stocks on average by 14%, 81%, and 7%, respectively, resulting in a net growth in C stock density of 14%. Although wildfire activities increased in recent decades, harvest was the key driver in the forest C balance in all regions for most of the observed timeframe.

Climate change mitigation potential of Louisiana's coastal area: Current estimates and future projections

Coastal habitats can play an important role in climate change mitigation. As Louisiana implements its climate action plan and the restoration and risk-reduction projects outlined in its 2017 Louisiana Coastal Master Plan, it is critical to consider potential greenhouse gas (GHG) fluxes in coastal habitats. This study estimated the potential climate mitigation role of existing, converted, and restored coastal habitats for years 2005, 2020, 2025, 2030, and 2050, which align with the Governor of Louisiana's GHG reduction targets. An analytical framework was developed that considered (1) available scientific data on net ecosystem carbon balance fluxes per habitat and (2) habitat areas projected from modeling efforts used for the 2017 Louisiana Coastal Master Plan to estimate the net GHG flux of coastal area. The coastal area was estimated as net GHG sinks of -38.4 ± 10.6 and -43.2 ± 12.0 Tg CO₂ equivalents (CO₂ e) in 2005 and 2020, respectively. The coastal area was projected to remain a net GHG sink in 2025 and 2030, both with and without the implementation of Coastal Master Plan projects (means ranged from -25.3 to -34.2 Tg CO₂ e). By 2050, with model-projected wetland loss and conversion of coastal habitats to open water due to coastal erosion and relative sea level rise, Louisiana's coastal area was projected to become a net source of GHG emissions both with and without the Coastal Master Plan projects. However, in the year 2050, the Louisiana Coastal Master Plan project implementation was projected to avoid the release of +8.8 ± 1.3 Tg CO₂ e compared with an alternative with no action. Reduction in current and future stressors to coastal habitats, including impacts from sea level rise, as well as the implementation of restoration projects could help to ensure coastal areas remain a natural climate solution.

Whales in the carbon cycle: can recovery remove carbon dioxide?

The great whales (baleen and sperm whales), through their massive size and wide distribution, influence ecosystem and carbon dynamics. Whales directly store carbon in their biomass and contribute to carbon export through sinking carcasses. Whale excreta may stimulate phytoplankton growth and capture atmospheric CO2; such indirect pathways represent the greatest potential for whale-carbon sequestration but are poorly understood. We quantify the carbon values of whales while recognizing the numerous ecosystem, cultural, and moral motivations to protect them. We also propose a framework to quantify the economic value of whale carbon as populations change over time. Finally, we suggest research to address key unknowns (e.g., bioavailability of whale-derived nutrients to phytoplankton, species- and region-specific variability in whale carbon contributions).

CaRPE: the Carbon Reduction Potential Evaluation tool for building climate mitigation scenarios on US agricultural lands

The Carbon Reduction Potential Evaluation (CaRPE) tool is a web-based interactive tool that integrates two databases for the USA collected at county/multi-county scales to visualize and estimate the climate benefits of implementing a variety of conservation practices on croplands and grazing lands. The COMET-Planner tool provides county/multi-county carbon sequestration and greenhouse gas emission reduction coefficients associated with the adoption of climate-smart agricultural management practices. The CaRPE tool couples these coefficients, reported in tonnes of carbon dioxide equivalents (CO2e) per acre per year, with county-level cropland and grazing land acres extracted from the US Agricultural Census. The CaRPE graphical user interface allows users to quickly and easily build and export scenarios of new conservation practice adoption on desired acreages and locations at state, regional or national scales. Results are in tonnes CO2e per year, and each scenario can be exported in tabular and map formats at the selected scales. Existing county-level cropland acreage data provide the upper boundaries for acres of adoption and can be modified based on specific goals established by the user.The output may be used to develop potential targets of adoption and help inform decisions related to resource prioritization and planning efforts. In collaboration with local experts and farmer-led organizations, the results can provide a key starting block to prioritize practices and areas that contribute to climate benefits. As the underlying databases and models are updated and improved, CaRPE can be revised accordingly to increase accuracy and enhance applicability. The CaRPE tool and the user guide are available at: Database URL: https://carpe.shinyapps.io/CarpeTool/.

Divergent responses of cropland soil organic carbon to warming across the Sichuan Basin of China

Cropland soils are considered to have the potential to sequester carbon (C). Warming can increase soil organic C (SOC) by enhancing primary production, but it can also cause carbon release from soils. However, the role of warming in governing cropland SOC dynamics over broad geographic scales remains poorly understood. Using over 4000 soil samples collected in the 1980s and 2010s across the Sichuan Basin of China, this study assessed the warming-induced cropland SOC change and the correlations with precipitation, cropland type and soil type. Results showed mean SOC content increased from 11.10 to 13.85 g C kg^-1. Larger SOC increments were observed under drier conditions (precipitation < 1050 mm, dryland and paddy-dryland rotation cropland), which were 1.67-2.23 times higher than under wetter conditions (precipitation > 1050 mm and paddy fields). Despite the significant associations of SOC increment with crop productivity, precipitation, fertilization, cropland type and soil type, warming also acted as one of major contributors to cropland SOC change. The SOC increment changed parabolically with the rise in temperature increase rate under relatively drier conditions, while temperature increase had no impact on cropland SOC increment under wetter conditions. Meanwhile, the patterns of the parabolical relationship varied with soil types in drylands, where the threshold of temperature increase rate, the point at which the SOC increment switched from increasing to decreasing with warming, was lower for clayey soils (Ali-Perudic Argosols) than for sandy soils (Purpli-Udic Cambosols). These results illustrate divergent responses of cropland SOC to warming under different environments, which were contingent on water conditions and soil types. Our findings emphasize the importance of formulating appropriate field water management for sustainable C sequestration and the necessity of incorporating environment-specific mechanisms in Earth system models for better understanding of the soil C-climate feedback in complex environments.

Nature-based climate solutions require a mix of socioeconomic and governance attributes

Nature-based climate solutions (NCS) can play a crucial role in reducing climate change. There is, however, a lack of understanding of the biophysical, social, and political contexts surrounding NCS, which hampers its practical implementation. Here, we used estimates of carbon sink potential to identify socioeconomic and ecological factors that may stimulate NCS implementation in developing economies. We considered carbon sink potential for eight NCS, including reforestation, peatland restoration, natural forest management, improved rice cultivation, optimal grazing intensity, grazing (legumes), avoided peatland impacts, and avoided coastal impacts. Food insecurity hotspots, which currently receive the most development aid, have the lowest likelihood of realizing NCS' potential. Poor governance structures and food insecurity impede the implementation of NCS projects at the country level. By carefully assessing complementary food security, sustainable financing, and soil quality safeguards, NCS as a nationally determined contribution to climate mitigation can be made more effective.

Rapid carbon accumulation at a saltmarsh restored by managed realignment exceeded carbon emitted in direct site construction

Increasing attention is being paid to the carbon sequestration and storage services provided by coastal blue carbon ecosystems such as saltmarshes. Sites restored by managed realignment, where existing sea walls are breached to reinstate tidal inundation to the land behind, have considerable potential to accumulate carbon through deposition of sediment brought in by the tide and burial of vegetation in the site. While this potential has been recognised, it is not yet a common motivating factor for saltmarsh restoration, partly due to uncertainties about the rate of carbon accumulation and how this balances against the greenhouse gases emitted during site construction. We use a combination of field measurements over four years and remote sensing to quantify carbon accumulation at a large managed realignment site, Steart Marshes, UK. Sediment accumulated rapidly at Steart Marshes (mean of 75 mm yr-1) and had a high carbon content (4.4% total carbon, 2.2% total organic carbon), resulting in carbon accumulation of 36.6 t ha-1 yr-1 total carbon (19.4 t ha-1 yr-1 total organic carbon). This rate of carbon accumulation is an order of magnitude higher than reported in many other restored saltmarshes, and is somewhat higher than values previously reported from another hypertidal system (Bay of Fundy, Canada). The estimated carbon emissions associated with the construction of the site were ~2-4% of the observed carbon accumulation during the study period, supporting the view that managed realignment projects in such settings may have significant carbon accumulation benefits. However, uncertainties such as the origin of carbon (allochthonous or autochthonous) and changes in gas fluxes need to be resolved to move towards a full carbon budget for saltmarsh restoration.

Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands

Coastal wetlands provide key ecosystem services, including substantial long-term storage of atmospheric CO₂ in soil organic carbon pools. This accumulation of soil organic matter is a vital component of elevation gain in coastal wetlands responding to sea-level rise. Anthropogenic activities that alter coastal wetland function through disruption of tidal exchange and wetland water levels are ubiquitous. This study assesses soil vertical accretion and organic carbon accretion across five coastal wetlands that experienced over a century of impounded hydrology, followed by restoration of tidal exchange 5 to 14 years prior to sampling. Nearby marshes that never experienced tidal impoundment served as controls with natural hydrology to assess the impact of impoundment and restoration. Dated soil cores indicate that elevation gain and carbon storage were suppressed 30-70 % during impoundment, accounting for the majority of elevation deficit between impacted and natural sites. Only one site had substantial subsidence, likely due to oxidation of soil organic matter. Vertical and carbon accretion gains were achieved at all restored sites, with carbon burial increasing from 96 ± 33 to 197 ± 64 g C m^-2 y^-1. The site with subsidence was able to accrete at double the rate (13 ± 5.6 mm y^-1) of the natural complement, due predominantly to organic matter accumulation rather than mineral deposition, indicating these ecosystems are capable of large dynamic responses to restoration when conditions are optimized for vegetation growth. Hydrologic restoration enhanced elevation resilience and climate benefits of these coastal wetlands.

Response of soil respiration to changes in soil temperature and water table level in drained and restored peatlands of the southeastern United States

BACKGROUND

Extensive drainage of peatlands in the southeastern United States coastal plain for the purposes of agriculture and timber harvesting has led to large releases of soil carbon as carbon dioxide (CO₂) due to enhanced peat decomposition. Growth in mechanisms that provide financial incentives for reducing emissions from land use and land-use change could increase funding for hydrological restoration that reduces peat CO₂ emissions from these ecosystems. Measuring soil respiration and physical drivers across a range of site characteristics and land use histories is valuable for understanding how CO₂ emissions from peat decomposition may respond to raising water table levels. We combined measurements of total soil respiration, depth to water table from soil surface, and soil temperature from drained and restored peatlands at three locations in eastern North Carolina and one location in southeastern Virginia to investigate relationships among total soil respiration and physical drivers, and to develop models relating total soil respiration to parameters that can be easily measured and monitored in the field.

RESULTS

Total soil respiration increased with deeper water tables and warmer soil temperatures in both drained and hydrologically restored peatlands. Variation in soil respiration was more strongly linked to soil temperature at drained (R² = 0.57, p < 0.0001) than restored sites (R² = 0.28, p < 0.0001).

CONCLUSIONS

The results suggest that drainage amplifies the impact of warming temperatures on peat decomposition. Proxy measurements for estimation of CO₂ emissions from peat decomposition represent a considerable cost reduction compared to direct soil flux measurements for land managers contemplating the potential climate impact of restoring drained peatland sites. Research can help to increase understanding of factors influencing variation in soil respiration in addition to physical variables such as depth to water table and soil temperature.

Using remote sensing to quantify the additional climate benefits of California forest carbon offset projects

Nature-based climate solutions are a vital component of many climate mitigation strategies, including California's, which aims to achieve carbon neutrality by 2045. Most carbon offsets in California's cap-and-trade program come from improved forest management (IFM) projects. Since 2012, various landowners have set up IFM projects following the California Air Resources Board's IFM protocol. As many of these projects approach their 10th year, we now have the opportunity to assess their effectiveness, identify best practices, and suggest improvements toward future protocol revisions. In this study, we used remote sensing-based datasets to evaluate the carbon trends and harvest histories of 37 IFM projects in California. Despite some current limitations and biases, these datasets can be used to quantify carbon accumulation and harvest rates in offset project lands relative to nearby similar "control" lands before and after the projects began. Five lines of evidence suggest that the carbon accumulated in offset projects to date has generally not been additional to what might have otherwise occurred: (1) most forests in northwestern California have been accumulating carbon since at least the mid-1980s and continue to accumulate carbon, whether enrolled in offset projects or not; (2) harvest rates were high in large timber company project lands before IFM initiation, suggesting they are earning carbon credits for forests in recovery; (3) projects are often located on lands with higher densities of low-timber-value species; (4) carbon accumulation rates have not yet increased on lands that enroll as offset projects, relative to their pre-enrollment levels; and (5) harvest rates have not decreased on most project lands since offset project initiation. These patterns suggest that the current protocol should be improved to robustly measure and reward additionality. In general, our framework of geospatial analyses offers an important and independent means to evaluate the effectiveness of the carbon offsets program, especially as these data products continue improving and as offsets receive attention as a climate mitigation strategy.

Annual carbon sequestration and loss rates under altered hydrology and fire regimes in southeastern USA pocosin peatlands

Peatlands drained for agriculture or forestry are susceptible to the rapid release of greenhouse gases (GHGs) through enhanced microbial decomposition and increased frequency of deep peat fires. We present evidence that rewetting drained subtropical wooded peatlands (STWPs) along the southeastern USA coast, primarily pocosin bogs, could prevent significant carbon (C) losses. To quantify GHG emissions and storage from drained and rewetted pocosin we used eddy covariance techniques, the first such estimates that have been applied to this major bog type, on a private drained (PD) site supplemented by static chamber measurements at PD and Pocosin Lakes National Wildlife Refuge. Net ecosystem exchange measurements showed that the loss was 21.2 Mg CO₂  ha^-1  year^-1 (1 Mg = 10⁶  g) in the drained pocosin. Under a rewetted scenario, where the annual mean water table depth (WTD) decreased from 60 to 30 cm, the C loss was projected to fall to 2 Mg CO₂  ha^-1  year^-1 , a 94% reduction. If the WTD was 20 cm, the peatlands became a net carbon sink (-3.3 Mg CO₂  ha^-1  year^-1 ). Hence, net C reductions could reach 24.5 Mg CO₂  ha^-1  year^-1 , and when scaled up to the 4000 ha PD site nearly 100,000 Mg CO₂  year^-1 of creditable C could be amassed. We conservatively estimate among the 0.75 million ha of southeastern STWPs, between 450 and 770 km² could be rewet, reducing annual GHG emissions by 0.96-1.6 Tg (1 Tg = 10¹²  g) of CO₂ , through suppressed microbial decomposition and 1.7-2.8 Tg via fire prevention, respectively. Despite covering <0.01% of US land area, rewetting drained pocosin can potentially provide 2.4% of the annual CO₂ nationwide reduction target of 0.18 Pg (1 Pg = 10¹⁵  g). Suggesting pocosin restoration can contribute disproportionately to the US goal of achieving net-zero emission by 2050.

The United States and China on the paths and policies to carbon neutrality

The rapid economic development has highlighted the global climate change problem and carbon dioxide emissions have brought challenges to global climate change. The combined carbon emissions of the United States and China are nearly half of global carbon emissions. These two countries have made great contributions to environmental protection and responded actively to global warming, and set the goal of carbon neutrality. This study takes the United States and China as examples to compare their national paths and policies to achieve carbon neutrality while also analyzing the stage effects of carbon emission reduction in these two countries. This study found that the policy systems in the United States and China are opposites of each other. The United States is a "Bottom to Top" system while China is a "Top to Bottom". The CO₂ emission in the United States is currently in the absolute carbon emission reduction period, that is, the reduction of total carbon emissions; while China is in the relative carbon emission reduction period, that is, the reduction of carbon emission intensity. China's transition time from carbon peaking to carbon neutrality is shorter than that of the United States, which is a huge challenge for China because its population is much larger than that of the United States. The results of this research can be used by other countries and regions for supporting carbon reduction policy decision-making and achieving UN sustainable development goals (SDGs).

An integrated approach to estimate how much urban afforestation can contribute to move towards carbon neutrality

Urban afforestation is considered a promising nature-climate solution that may contribute to achieve climate neutrality by 2050, since it can increase C-storage and C-sequestration, whilst providing further multiple ecosystem services for citizens. However, the quantification of the CO₂ sequestration capacity that may be provided by an urban forest as well as the capacity to impact the city-level C-balance and offset anthropogenic emissions is a complex issue. Methodological approaches, quantity and quality of information contained in urban tree database, and the level of detail of the planned urban forest can strongly influence the estimation of C-sequestration potential offered by urban forests. In this work, an integrated framework based on emission inventory, tree species/morphology and ecosystem modelling has been proposed for the city of Prato, Italy, a representative medium size European city to: i) evaluate the current C-sequestration capacity of urban trees; ii) upscale such capacity with different afforestation scenarios, iii) compare the sink capacity offered by ecosystems with current and projected anthropogenic emissions. Results indicated that the green areas within the Municipality of Prato can sequester 33.1 ktCO₂ yr^-1 under actual conditions and 51.0 ktCO₂ yr^-1 under the afforestation scenario which maximize the CO₂ sequestration capacity, offsetting the 7.1 % and 11 % of the total emissions (465.8 ktCO₂ yr^-1), respectively. This study proves that, in the various afforestation scenarios tested, the contribution of urban afforestation to the municipality carbon balance is negligible and that carbon neutrality can only be reached by the substantial decarbonization of emission sectors.

Future land-use competition constrains natural climate solutions

Natural climate solutions (NCS) are an essential complement to climate mitigation and have been increasingly incorporated into international mitigation strategies. Yet, with the ongoing population growth, allocating natural areas for NCS may compete with other socioeconomic priorities, especially urban development and food security. Here, we projected the impacts of land-use competition incurred by cropland and urban expansion on the climate mitigation potential of NCS. We mapped the areas available for implementing 9 key NCS strategies and estimated their climate change mitigation potential. Then, we overlaid these areas with future cropland and urban expansion maps projected under three Shared Socioeconomic Pathway (SSP) scenarios (2020-2100) and calculated the resulting mitigation potential loss of each selected NCS strategy. Our results estimate a substantial reduction, 0.3-2.8 GtCO₂ yr^-1 or 4-39 %, in NCS mitigation potential, of which cropland expansion for fulfilling future food demand is the primary cause. This impact is particularly severe in the tropics where NCS hold the most abundant mitigation potential. Our findings highlight immediate actions prioritized to tropical areas are important to best realize NCS and are key to developing realistic and sustainable climate policies.

Grassland soil carbon sequestration: Current understanding, challenges, and solutions

Grasslands store approximately one third of the global terrestrial carbon stocks and can act as an important soil carbon sink. Recent studies show that plant diversity increases soil organic carbon (SOC) storage by elevating carbon inputs to belowground biomass and promoting microbial necromass contribution to SOC storage. Climate change affects grassland SOC storage by modifying the processes of plant carbon inputs and microbial catabolism and anabolism. Improved grazing management and biodiversity restoration can provide low-cost and/or high-carbon-gain options for natural climate solutions in global grasslands. The achievable SOC sequestration potential in global grasslands is 2.3 to 7.3 billion tons of carbon dioxide equivalents per year (CO₂e year^-1) for biodiversity restoration, 148 to 699 megatons of CO₂e year^-1 for improved grazing management, and 147 megatons of CO₂e year^-1 for sown legumes in pasturelands.

Impoundment increases methane emissions in Phragmites-invaded coastal wetlands

Saline tidal wetlands are important sites of carbon sequestration and produce negligible methane (CH₄ ) emissions due to regular inundation with sulfate-rich seawater. Yet, widespread management of coastal hydrology has restricted tidal exchange in vast areas of coastal wetlands. These ecosystems often undergo impoundment and freshening, which in turn cause vegetation shifts like invasion by Phragmites, that affect ecosystem carbon balance. Understanding controls and scaling of carbon exchange in these understudied ecosystems is critical for informing climate consequences of blue carbon restoration and/or management interventions. Here, we (1) examine how carbon fluxes vary across a salinity gradient (4-25 psu) in impounded and natural, tidally unrestricted Phragmites wetlands using static chambers and (2) probe drivers of carbon fluxes within an impounded coastal wetland using eddy covariance at the Herring River in Wellfleet, MA, United States. Freshening across the salinity gradient led to a 50-fold increase in CH₄ emissions, but effects on carbon dioxide (CO₂ ) were less pronounced with uptake generally enhanced in the fresher, impounded sites. The impounded wetland experienced little variation in water-table depth or salinity during the growing season and was a strong CO₂ sink of -352 g CO₂ -C m^-2  year^-1 offset by CH₄ emission of 11.4 g CH₄ -C m^-2  year^-1 . Growing season CH₄ flux was driven primarily by temperature. Methane flux exhibited a diurnal cycle with a night-time minimum that was not reflected in opaque chamber measurements. Therefore, we suggest accounting for the diurnal cycle of CH₄ in Phragmites, for example by applying a scaling factor developed here of ~0.6 to mid-day chamber measurements. Taken together, these results suggest that although freshened, impounded wetlands can be strong carbon sinks, enhanced CH₄ emission with freshening reduces net radiative balance. Restoration of tidal flow to impounded ecosystems could limit CH₄ production and enhance their climate regulating benefits.

Land-based climate solutions for the United States

Meeting end-of-century global warming targets requires aggressive action on multiple fronts. Recent reports note the futility of addressing mitigation goals without fully engaging the agricultural sector, yet no available assessments combine both nature-based solutions (reforestation, grassland and wetland protection, and agricultural practice change) and cellulosic bioenergy for a single geographic region. Collectively, these solutions might offer a suite of climate, biodiversity, and other benefits greater than either alone. Nature-based solutions are largely constrained by the duration of carbon accrual in soils and forest biomass; each of these carbon pools will eventually saturate. Bioenergy solutions can last indefinitely but carry significant environmental risk if carelessly deployed. We detail a simplified scenario for the United States that illustrates the benefits of combining approaches. We assign a portion of non-forested former cropland to bioenergy sufficient to meet projected mid-century transportation needs, with the remainder assigned to nature-based solutions such as reforestation. Bottom-up mitigation potentials for the aggregate contributions of crop, grazing, forest, and bioenergy lands are assessed by including in a Monte Carlo model conservative ranges for cost-effective local mitigation capacities, together with ranges for (a) areal extents that avoid double counting and include realistic adoption rates and (b) the projected duration of different carbon sinks. The projected duration illustrates the net effect of eventually saturating soil carbon pools in the case of most strategies, and additionally saturating biomass carbon pools in the case of forest management. Results show a conservative end-of-century mitigation capacity of 110 (57-178) Gt CO₂ e for the U.S., ~50% higher than existing estimates that prioritize nature-based or bioenergy solutions separately. Further research is needed to shrink uncertainties, but there is sufficient confidence in the general magnitude and direction of a combined approach to plan for deployment now.

Decline in the suitable habitat of dominant Abies species in response to climate change in the Hindu Kush Himalayan region: insights from species distribution modelling

Reliable predictions of future distribution ranges of ecologically important species in response to climate change are required for developing effective management strategies. Here we used an ensemble modelling approach to predict the distribution of three important species of Abies namely, Abies pindrow, Abies spectabilis and Abies densa in the Hindu Kush Himalayan region under the current and two shared socioeconomic pathways (SSP245 and SSP585) and time periods of 2050 and 2090s. A correlative ensemble model using presence/absence data of the three Abies species and 22 environmental variables, including 19 bioclimatic variables and 3 topographic variables, from known distributions was built to predict the potential current and future distribution of these species. The individual models used to build the final ensemble performed well and provided reliable results for both the current and future distribution of all three species. For A. pindrow, precipitation of the driest month (Bio14) was the most important environmental variable with 83.3% contribution to model output while temperature seasonality (Bio4) and annual mean diurnal range (Bio2) were the most important variables for A. spectabilis and A. densa with 48.4% and 46.1% contribution to final model output, respectively. Under current climatic conditions, the ensemble models projected a total suitable habitat of about 433,003 km², 790,837 km² and 676,918 km² for A. pindrow, A. spectabilis and A. densa, respectively, which is approximately 10.36%, 18.91% and 16.91% of the total area of Hindu Kush Himalayan region. Projections of habitat suitability under future climate scenarios for all the shared socioeconomic pathways showed a reduction in potentially suitable habitats with a maximum overall loss of approximately 14% of the total suitable area of A. pindrow under SSP 8.5 by 2090. A decline in total suitable habitat is predicted to be 9.6% in A. spectabilis by 2090 under the SSP585 scenario while in A. densa 6.67% loss in the suitable area is expected by 2050 under the SSP585 scenario. Furthermore, there is no elevational change predicted in the case of A. pindrow while A. spectabilis is expected to show an upward shift by about 29 m per decade and A. densa is showing a downward shift at a rate of 11 m per decade. The results are interesting, and intriguing given the occurrence of these species across the Hindu Kush Himalayan region. Thus, our study underscores the need for consideration of unexpected responses of species to climate change and formulation of strategies for better forest management and conservation of important conifer species, such as A. pindrow, A. spectabilis and A. densa.

A Typology of Nature-Based Solutions for Sustainable Development: An Analysis of Form, Function, Nomenclature, and Associated Applications

This study presents a typology of nature-based solutions (NbS), addressing the need for a standardized source of definitions and nomenclature, and to facilitate communication in this interdisciplinary field of theory and practice. Growing usage of the umbrella phrase ‘nature-based solutions’ has led to a broad inclusion of terms. With the diversity of terminology used, the full potential of NbS may be lost in the confusion of misapplied terms. Standardization and definition of commonly used nature-based nomenclature are necessary to facilitate communication in this rapidly expanding field. Through objective systemization of applications, functions, and benefits, NbS can be embraced as a standard intervention to address societal challenges and support achievement of the UN SDGs.

Carbon conundrums: Do United States' current carbon market baselines represent an undesirable ecological threshold?

Relative frequency distribution of observed annual mortality expressed in aboveground (AG) carbon (C) (Mg CO₂ e ha^-1 year^-1 ) summarized across supersections by forest type [Hardwood (HW) vs. Softwood (SW)] and site class (Low vs. High) based on approximately 130,000 remeasured USDA Forest Service Forest Inventory and Analysis plots across the US. Top panel summarizes conditions in plots that do and do not meet the California Air Resources Board standards based on total basal area, whereas bottom panel summarizes conditions in plots falling inside and outside of optimum relative density levels. The latter represents a biophysically-informed approach accounting for changes in tree (and carbon) packing over forest development.

Lowering the Temperature to Increase Heat Equity: A Multi-Scale Evaluation of Nature-Based Solutions in Toronto, Ontario, Canada

Nature-based solutions (NbS) present an opportunity to reduce rising temperatures and the urban heat island effect. A multi-scale study in Toronto, Ontario, Canada, evaluates the effect of NbS on air and land surface temperature through two field campaigns at the micro and meso scales, using in situ measurements and LANDSAT imagery. This research demonstrates that the application of NbS in the form of green infrastructure has a beneficial impact on urban climate regimes with measurable reductions in air and land surface temperatures. Broad implementation of green infrastructure is a sustainable solution to improve the urban climate, enhance heat and greenspace equity, and increase resilience.

The global potential for increased storage of carbon on land

SignificanceDespite increased interest in land-based carbon storage as a climate solution, there are physical limits on how much additional carbon can be incorporated into terrestrial ecosystems. To effectively determine where and how to act, jurisdictions need robust data illustrating the magnitude and distribution of opportunities to increase carbon storage, as well as information on the actions available to achieve that storage. Here, we provide globally consistent maps for directing additional carbon storage under current and future climate, as well as a framework for determining how that storage could be gained through restoration, improved management, or maintenance of woody biomass and soil organic matter. Our estimates provide an upper bound on how improved land stewardship can mitigate the climate crisis.

Informing Nature-based Climate Solutions for the United States with the best-available science

Nature-based Climate Solutions (NbCS) are managed alterations to ecosystems designed to increase carbon sequestration or reduce greenhouse gas emissions. While they have growing public and private support, the realizable benefits and unintended consequences of NbCS are not well understood. At regional scales where policy decisions are often made, NbCS benefits are estimated from soil and tree survey data that can miss important carbon sources and sinks within an ecosystem, and do not reveal the biophysical impacts of NbCS for local water and energy cycles. The only direct observations of ecosystem-scale carbon fluxes, for example, by eddy covariance flux towers, have not yet been systematically assessed for what they can tell us about NbCS potentials, and state-of-the-art remote sensing products and land-surface models are not yet being widely used to inform NbCS policymaking or implementation. As a result, there is a critical mismatch between the point- and tree-scale data most often used to assess NbCS benefits and impacts, the ecosystem and landscape scales where NbCS projects are implemented, and the regional to continental scales most relevant to policymaking. Here, we propose a research agenda to confront these gaps using data and tools that have long been used to understand the mechanisms driving ecosystem carbon and energy cycling, but have not yet been widely applied to NbCS. We outline steps for creating robust NbCS assessments at both local to regional scales that are informed by ecosystem-scale observations, and which consider concurrent biophysical impacts, future climate feedbacks, and the need for equitable and inclusive NbCS implementation strategies. We contend that these research goals can largely be accomplished by shifting the scales at which pre-existing tools are applied and blended together, although we also highlight some opportunities for more radical shifts in approach.