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International climate goals imply reaching net-zero global carbon dioxide (CO2) emissions by roughly mid-century. Among the most difficult emissions to avoid will be those from modern aviation given the industry’s need for energy-dense liquid fuels and the lack of commercially competitive substitutes. Here, we systematically assess pathways to net-zero emissions aviation, exploring the potential contribution of different approaches as well as their social, technical, and economic limits. We find that ambitious reductions in demand for air transport and improvements in the energy efficiency of aircraft might avoid up to 62% and 26%, respectively, of projected business-as-usual aviation emissions in 2050. However, further reductions will depend on replacing fossil jet fuel with very large quantities of net-zero emissions biofuels or synthetic fuels (2.5-21 EJ)—which are currently much more expensive. Our results may inform investments and priorities for innovation by highlighting plausible pathways to net-zero emissions aviation, including the relative potential and trade-offs of changes in behavior, technology, and energy sources.

Limiting global warming to under 2°C would require stringent mitigation and likely additional carbon dioxide removals (CDR) to compensate for hard-to-avoid emissions. The relatively low cost and potential co-benefits of biochar as a soil amendment has gained attention in this context. We use a global multisector model to analyze biochar deployment in the context of energy system uses of biomass with CDR under different carbon price trajectories. We find that biochar can create an annual sink of up to 2.8 GtCO2, reducing global mean temperature increases by an additional 0.5-1.8% across scenarios by 2100 for a given carbon price path. In our scenarios, biochar’s deployment is dependent on potential crop yield gains and application rates, and the competition for resources with other CDR measures. We find that biochar can serve as a competitive CDR strategy, especially at lower carbon prices when bioenergy with carbon capture and storage is not economical.

The goal of this study is to analyze decarbonization pathways for Taiwan, in line with the goals of the Paris Agreement: achieving a 2 °C increase by 2100, aiming for 1.5 °C. We use GCAM, an integrated assessment model, in order to evaluate the different implications of decarbonization in this region. We find that, if Taiwan wants to be consistent with Paris’ goals, it needs an aggressive electrification of end-use sectors, a rapid scale-up of renewable energies, as well as increased efficiencies in buildings, transportation and industry. Transportation and industry present greater decarbonization challenges than buildings, and negative emission technologies become crucial. We also identify opportunities where future research would enrich decarbonization analyses for Taiwan.

About 78% of global greenhouse gas emissions between 1970 and 2010 were due to fossil fuel combustion, increasing the atmospheric mixing ratio of carbon dioxide to around 419 ppm by June 2021. During a similar period, between 1975 and 2017, 162 countries adopted renewable energy targets – official national commitments to increase the share of renewable energies. What induced the diffusion of these renewable energy targets? What are the patterns of their diffusion? We analyze data from 187 countries and assess four possible mechanisms of policy diffusion of renewable energy targets: learning, economic competition, emulation, and coercion. Using a qualitative comparative analysis, we find eight pathways to renewable energy target adoption. In the most common pathways, economic competition, emulation, and coercion played a significant role. Before there is a critical mass of countries to emulate, our analysis shows that early adopters followed the mechanisms of economic competition and coercion. Ultimately, we find that there is no one recipe for the diffusion of renewable energy targets, and we identify the specific countries associated with the different diffusion pathways.

Hydropower accounts for approximately 60% of electricity generation in Canada, with growth expected in the coming decades as part of renewable energy transitions; however, frequent cost overruns threaten the viability of this growth. Using the integrated assessment model GCAM, we develop an endogenous representation of hydropower for Canada that accounts for market dynamics, thus permitting analysis of hydropower competition with other electricity generation technologies, both with and without cost overruns. Results show that modelling hydropower resources endogenously increases Canadian hydropower deployment relative to an assumption of fixed hydropower production, from 417 to 495 TWh annually by 2050. In scenarios that apply cost overruns at historical levels, hydropower loses market share to more easily scalable technologies like wind power. When including high cost overrun assumptions, the model determines that hydropower falls from about 73% to 65% of Canadian electricity generation by 2050, while wind power increases from about 8% to 11%. Countries may be better able to achieve electrification and renewable energy targets at lower cost by avoiding large-scale, overrun-prone hydropower and nuclear generation projects. Model results support that cost overruns are important considerations for policy decisions related to electricity sector development in Canada and elsewhere.