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Stabilizing climate change well below 2 °C and towards 1.5 °C requires comprehensive mitigation of all greenhouse gases (GHG), including both CO 2 and non-CO 2 GHG emissions. Here we incorporate the latest global non-CO 2 emissions and mitigation data into a state-of-the-art integrated assessment model GCAM and examine 90 mitigation scenarios pairing different levels of CO 2 and non-CO 2 GHG abatement pathways. We estimate that when non-CO 2 mitigation contributions are not fully implemented, the timing of net-zero CO 2 must occur about two decades earlier. Conversely, comprehensive GHG abatement that fully integrates non-CO 2 mitigation measures in addition to a net-zero CO 2 commitment can help achieve 1.5 °C stabilization. While decarbonization-driven fuel switching mainly reduces non-CO 2 emissions from fuel extraction and end use, targeted non-CO 2 mitigation measures can significantly reduce fluorinated gas emissions from industrial processes and cooling sectors. Our integrated modeling provides direct insights in how system-wide all GHG mitigation can affect the timing of net-zero CO 2 for 1.5 °C and 2 °C climate change scenarios. Stabilizing climate change requires simultaneous mitigation of all greenhouse gas emissions (GHGs). Here the authors examine 90 mitigation scenarios pairing different levels of CO 2 and non-CO 2 GHG abatement pathways to demonstrate the contributions of different GHGs towards 1.5 °C and 2 °C goals.

Bioenergy with carbon capture and storage (BECCS) is considered a potential source of net negative carbon emissions and, if deployed at sufficient scale, could help reduce carbon dioxide emissions and concentrations. However, the viability and economic consequences of large-scale BECCS deployment are not fully understood. We use the Global Change Assessment Model (GCAM) integrated assessment model to explore the potential global and regional economic impacts of BECCS. As a negative-emissions technology, BECCS would entail a net subsidy in a policy environment in which carbon emissions are taxed. We show that by mid-century, in a world committed to limiting climate change to 2 °C, carbon tax revenues have peaked and are rapidly approaching the point where climate mitigation is a net burden on general tax revenues. Assuming that the required policy instruments are available to support BECCS deployment, we consider its effects on global trade patterns of fossil fuels, biomass, and agricultural products. We find that in a world committed to limiting climate change to 2 °C, the absence of CCS harms fossil-fuel exporting regions, while the presence of CCS, and BECCS in particular, allows greater continued use and export of fossil fuels. We also explore the relationship between carbon prices, food-crop prices and use of BECCS. We show that the carbon price and biomass and food crop prices are directly related. We also show that BECCS reduces the upward pressure on food crop prices by lowering carbon prices and lowering the total biomass demand in climate change mitigation scenarios. All of this notwithstanding, many challenges, both technical and institutional, remain to be addressed before BECCS can be deployed at scale.

Food insecurity can be directly exacerbated by climate change due to crop-production-related impacts of warmer and drier conditions that are expected in important agricultural regions1–3. However, efforts to mitigate climate change through comprehensive, economy-wide GHG emissions reductions may also negatively affect food security, due to indirect impacts on prices and supplies of key agricultural commodities4–6. Here we conduct a multiple model assessment on the combined effects of climate change and climate mitigation efforts on agricultural commodity prices, dietary energy availability and the population at risk of hunger. A robust finding is that by 2050, stringent climate mitigation policy, if implemented evenly across all sectors and regions, would have a greater negative impact on global hunger and food consumption than the direct impacts of climate change. The negative impacts would be most prevalent in vulnerable, low-income regions such as sub-Saharan Africa and South Asia, where food security problems are already acute.

Currently responsible for over one fifth of carbon emissions worldwide, the transportation sector will need to undergo a substantial technological transition to ensure compatibility with global climate goals. Few studies have modeled strategies to achieve zero emissions across all transportation modes, including aviation and shipping, alongside an integrated analysis of feedbacks on other sectors and environmental systems. Here, we use a global integrated assessment model to evaluate deep decarbonization scenarios for the transportation sector consistent with maintaining end-of-century warming below 1.5 °C, considering varied timelines for fossil fuel phase-out and implementation of advanced alternative technologies. We highlight the leading low carbon technologies for each transportation mode, finding that electrification contributes most to decarbonization across the sector. Biofuels and hydrogen are particularly important for aviation and shipping. Our most ambitious scenario eliminates transportation emissions by mid-century, contributing substantially to achieving climate targets but requiring rapid technological shifts with integrated impacts on fuel demands and availability and upstream energy transitions. To eliminate transport emissions by 2050, low carbon fuels must rapidly replace fossil fuels. The authors model these technological transitions for each transport mode and evaluate economy-wide tradeoffs of varied levels of transport decarbonization.

Land use is at the core of various sustainable development goals. Long-term climate foresight studies have structured their recent analyses around five socio-economic pathways (SSPs), with consistent storylines of future macroeconomic and societal developments; however, model quantification of these scenarios shows substantial heterogeneity in land-use projections. Here we build on a recently developed sensitivity approach to identify how future land use depends on six distinct socio-economic drivers (population, wealth, consumption preferences, agricultural productivity, land-use regulation, and trade) and their interactions. Spread across models arises mostly from diverging sensitivities to long-term drivers and from various representations of land-use regulation and trade, calling for reconciliation efforts and more empirical research. Most influential determinants for future cropland and pasture extent are population and agricultural efficiency. Furthermore, land-use regulation and consumption changes can play a key role in reducing both land use and food-security risks, and need to be central elements in sustainable development strategies. There lacks model comparison of global land use change projections. Here the authors explored how different long-term drivers determine land use and food availability projections and they showed that the key determinants population growth and improvements in agricultural efficiency.

The war in Ukraine caused Europe to more than double its imports of liquefied natural gas (LNG) in only one year. In addition, imported LNG remains a crucial source of energy for resource-poor countries, such as Japan, where LNG imports satisfy about a quarter of the country’s primary energy demand. However, an increasing number of countries are formulating stringent decarbonization plans. Liquefied hydrogen and liquefied ammonia coupled with carbon capture and storage (LH 2 -CCS, LNH 3 -CCS) are emerging as the front runners in the search for low-carbon alternatives to LNG. Yet, little is currently known about the full environmental profile of LH 2 -CCS and LNH 3 -CCS because several characteristics of the two alternatives have only been analyzed in isolation in previous work. Here we show that the potential of these fuels to reduce greenhouse gas (GHG) emissions throughout the supply chain is highly uncertain. Our best estimate is that LH 2 -CCS and LNH 3 -CCS can reduce GHG emissions by 25%–61% relative to LNG assuming a 100 year global warming potential. However, directly coupling LNG with CCS would lead to substantial GHG reductions on the order of 74%. Further, under certain conditions, emissions from LH 2 -CCS and LNH 3 -CCS could exceed those of LNG, by up to 44%. These results question the suitability of LH 2 -CCS and LNH 3 -CCS for stringent decarbonization purposes.

Agricultural production is sensitive to weather and thus directly affected by climate change. Plausible estimates of these climate change impacts require combined use of climate, crop, and economic models. Results from previous studies vary substantially due to differences in models, scenarios, and data. This paper is part of a collective effort to systematically integrate these three types of models. We focus on the economic component of the assessment, investigating how nine global economic models of agriculture represent endogenous responses to seven standardized climate change scenarios produced by two climate and five crop models. These responses include adjustments in yields, area, consumption, and international trade. We apply biophysical shocks derived from the Intergovernmental Panel on Climate Change’s representative concentration pathway with end-of-century radiative forcing of 8.5 W/m2. The mean biophysical yield effect with no incremental CO2 fertilization is a 17% reduction globally by 2050 relative to a scenario with unchanging climate. Endogenous economic responses reduce yield loss to 11%, increase area of major crops by 11%, and reduce consumption by 3%. Agricultural production, cropland area, trade, and prices show the greatest degree of variability in response to climate change, and consumption the lowest. The sources of these differences include model structure and specification; in particular, model assumptions about ease of land use conversion, intensification, and trade. This study identifies where models disagree on the relative responses to climate shocks and highlights research activities needed to improve the representation of agricultural adaptation responses to climate change.

The Paris Agreement requires countries to articulate near-term emissions reduction strategies through to 2025 or 2030 by communicating nationally determined contributions (NDCs), as well as encouraging the formulation of long-term low-emission development strategies (Article 4.19) 1 . In response, many countries have either submitted or are preparing mid-century strategies 2 . Most NDCs set high-level near-term goals—such as limits on emissions or emissions intensity 3 —which do not provide information about the extent to which they lay the foundations of technology, infrastructure and institutions for deeper reductions in the future, which is a key question for decision makers. Here, using a state-level model of the US embedded within a global integrated assessment model 4 , 5 , we demonstrate that although the US NDC lies on a straight-line emissions pathway towards its mid-century strategy, the resulting energy system transitions involve nonlinear transformations. The rates of capacity additions and capital investments in electricity generation beyond 2025 are more than three times the rates during the next decade. Our results demonstrate the need for global stocktaking exercises to evaluate the NDCs using metrics broader than emissions to better illuminate their effectiveness in addressing the Paris Agreement’s long-term goals 6 , 7 . Achieving the longer-term goals of the Paris Agreement and transformation to a low-carbon society requires an acceleration in electricity generation investment and capacity addition above that outlined in the US Nationally Determined Contribution.

Representative Concentration Pathway (RCP) 4.5 is a scenario that stabilizes radiative forcing at 4.5 W m −2 in the year 2100 without ever exceeding that value. Simulated with the Global Change Assessment Model (GCAM), RCP4.5 includes long-term, global emissions of greenhouse gases, short-lived species, and land-use-land-cover in a global economic framework. RCP4.5 was updated from earlier GCAM scenarios to incorporate historical emissions and land cover information common to the RCP process and follows a cost-minimizing pathway to reach the target radiative forcing. The imperative to limit emissions in order to reach this target drives changes in the energy system, including shifts to electricity, to lower emissions energy technologies and to the deployment of carbon capture and geologic storage technology. In addition, the RCP4.5 emissions price also applies to land use emissions; as a result, forest lands expand from their present day extent. The simulated future emissions and land use were downscaled from the regional simulation to a grid to facilitate transfer to climate models. While there are many alternative pathways to achieve a radiative forcing level of 4.5 W m −2 , the application of the RCP4.5 provides a common platform for climate models to explore the climate system response to stabilizing the anthropogenic components of radiative forcing.

The Kingdom of Saudi Arabia (KSA) has pledged to achieve net-zero greenhouse gas emissions by 2060. Direct air carbon capture and storage (DACCS) is critical for the country to meet its net-zero target given its reliance on fossil fuels and limited options for carbon dioxide removal (CDR). However, the role of DACCS in KSA’s national climate change mitigation has not been studied in the literature. In this study, we aim to understand the potential role of DACCS and the effect of its deployment timing in KSA’s transition toward its net-zero target using the Global Change Analysis Model (GCAM)-KSA, which is a version of GCAM with KSA split out as an individual region. We find that the annual DACCS CO 2 sequestration in KSA reaches 0.28–0.33 Gt yr −1 by 2060 depending on its deployment timing. Early DACCS deployment, driven by its early and rapid cost reduction worldwide, could bring significant savings (∼420 billion USD during 2020–2060) in the cost of climate change mitigation in KSA, approximately 17% reduction relative to delayed DACCS deployment. Our study suggests a strong role for KSA to proactively invest in the R&D of DACCS, initiate early DACCS deployment, and explore a broad suite of CDR options.