Delayed climate mitigation could trigger a socioeconomic tipping point

Maximum Academic Press

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Using an integrated assessment model, the research finds that the social cost of carbon (SCC)—a key indicator guiding climate action—may rise with warming at first but then sharply decline once damages exceed a critical threshold. Such a decline would weaken global motivation to deploy renewable energy and could accelerate warming far beyond temperature goals.

Global temperatures are approaching 1.5 °C above pre-industrial levels, with projections indicating a high likelihood of surpassing 2 °C this century. Despite clear scientific warnings, global CO₂ emissions have rebounded following the COVID-19 pandemic due to stimulated consumption, fossil-fuel-locked infrastructure, and slow deployment of renewable energy. Economic inertia, workforce barriers, stranded fossil fuel assets, and inconsistent mitigation policies further hinder progress. Many countries continue to adopt a “wait-and-see” strategy based on the assumption that the SCC—and therefore the incentive for mitigation—will naturally increase as climate damages worsen. Based on these challenges, there is an urgent need to test whether delayed action may instead erode the incentive to mitigate.

A study (DOI:10.48130/een-0025-0012) published in Energy & Environment Nexus on 28 October 2025 by Rong Wang, Fudan University, highlights that waiting for climate damages to intensify before acting may undermine the very incentives needed to reduce fossil fuel use.

The study introduces a modified cost–benefit integrated assessment model designed to optimize long-term choices in consumption, labor, and investment while governing the pace of transition from fossil fuels to renewable energy. Using a CES production function calibrated with historical data, the model incorporates realistic elasticities between energy and nonenergy inputs, varying substitution possibilities between fossil and renewable energy, and empirically grounded learning rates that reflect past declines in renewable energy costs. An empirical climate-damage function further links rising temperatures to economic losses, with parameters aligned to recent evidence and the Paris Agreement’s temperature thresholds. Mitigation is triggered in different years by sharply reducing the pure rate of time preference, and 10,000 Monte Carlo simulations evaluate uncertainties across key factors such as technological progress, climate system response times, and the capacity of backstop technologies. The results reveal that mitigation costs grow steeply at deep decarbonization levels: a 50% reduction in fossil fuel supply lowers GDP by only about 5%–8%, whereas a 90% reduction can reduce GDP by 21%–51%, highlighting stringent technological and geophysical limits. The model also projects substantially higher damages at 2 °C warming—around 20%–50% of global GDP—than classic DICE-type models, better matching empirical assessments. If mitigation begins by 2025, renewable energy could reach roughly 90% of total supply by 2100, holding climate damages near 10% of GDP. In contrast, delaying action until after 2050 results in sluggish renewable deployment, damages nearing 30% of GDP, and a rapid decline in the social cost of carbon—often below USD 1,000/tCO₂—reducing the likelihood of limiting warming to 2 °C to under 10%. Sensitivity tests confirm that this pattern of initially rising but ultimately collapsing mitigation incentives is robust. Moreover, consistently low renewable energy shares once damages exceed about 10% of GDP may signal an approaching socioeconomic tipping point.

The study shows that waiting for rising climate damages will not strengthen mitigation incentives; instead, delaying action can weaken renewable energy adoption and entrench fossil fuel dependence. By revealing how a declining SCC aligns with slowing energy transitions, the research calls for an early-warning mechanism in the Global Stocktake to track climate damages and renewable energy shares. Such monitoring could signal when a socioeconomic tipping point is approaching, enabling timely policy intervention to avoid irreversible temperature overshoot.

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References

DOI

10.48130/een-0025-0012

Original Source URL

https://doi.org/10.48130/een-0025-0012

About Energy & Environment Nexus

Energy & Environment Nexus is a multidisciplinary journal for communicating advances in the science, technology and engineering of energy, environment and their Nexus.

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DOI

10.48130/een-0025-0012 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

A slower-than-needed scale-up of renewable energy might reduce the incentive for mitigation

 

LLMs choose friends and colleagues like people

PNAS Nexus

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image: 

Networks generated by LLM agents exhibiting “preferential attachment” (panel A), “triadic closure” (panel B), “homophily” (panel C), and “small-world” dynamics (panel D).

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Credit: Marios Papachristou and Yuan Yuan

When large language models (LLMs) make decisions about networking and friendship, the models tend to act like people, across both synthetic simulations and real-world network contexts. Marios Papachristou and Yuan Yuan developed a framework to study network formation behaviors of multiple LLM agents and compared these behaviors against human behaviors. The authors conducted simulations using several large language models placed in a network, which were asked to choose which other nodes to connect with, given their number of connections, common neighbors, and shared attributes, like arbitrarily assigned “hobbies” or “location.” The authors varied the network context, including simulations of friendships and workplace, communities; the amount of information provided to the agents; and model parameters like temperature. Generally, LLMs exhibited tendencies to connect to other nodes that were already well connected, a phenomenon called “preferential attachment.” LLMs also showed a tendency to connect to other nodes with a high number of common connections, a phenomenon called “triadic closure.” LLMs also demonstrated homophily, choosing nodes with similar hobbies or location, as well as the “small-world” phenomenon, where any two nodes are connected by surprisingly short chains of acquaintances often with just a few “degrees of separation.” In network simulations based on real Facebook friendship networks, work networks, and telecommunication networks, LLM models prioritized homophily most strongly, followed by triadic closure and preferential attachment. Finally, the authors conducted a controlled survey with around 100 human participants and asked participants and to respond to the same survey. LLMs' responses showed strong alignment with human link-formation choices, though the models displayed higher internal consistency than humans. According to the authors, these findings demonstrate the potential for LLMs to be used as a source of synthetic data when privacy concerns preclude using human data, but also raise questions regarding the design and alignment of artificial intelligence systems that make real-world decisions by interacting with human networks.

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Journal

PNAS Nexus

Article Title

Network formation and dynamics among multi-LLMs

Article Publication Date

2-Dec-2025

 

Gas stoves and nitrogen dioxide exposure

PNAS Nexus

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image: 

Indoor (gold) and outdoor (blue) average nitrogen dioxide exposures.

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Credit: Kashtan et al.

Twenty-two million Americans would no longer be breathing in unhealthy levels of nitrogen dioxide if they switched from gas and propane stoves to electric stoves. Robert Jackson and colleagues combined outdoor air quality data with estimates of indoor nitrogen dioxide emissions from stoves in more than fifteen cities. As outdoor air quality improves, stoves become an increasingly important source of exposure. According to the World Health Organization, health risks to the respiratory system increase at levels above 5.2 parts per billion by volume. Taking indoor and outdoor sources together, the authors found that average total residential long-term nitrogen dioxide exposure is approximately 10 parts per billion by volume for people with gas stoves and approximately 8 parts per billion by volume for those with electric stoves. For households in the 95th percentile of gas stove use, which corresponds to using multiple gas burners and a gas oven for multiple hours a day, stoves account for more than half of total nitrogen dioxide exposure. The authors estimate that approximately 22 million people whose outdoor nitrogen dioxide exposure falls below World Health Organization guidelines exceed those guidelines due to gas stove use. According to the authors, the study’s ZIP-code-level exposure maps could help identify regions to prioritize for indoor and outdoor air quality interventions, particularly in lower-income communities.

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Journal

PNAS Nexus

Article Title

Integrating indoor and outdoor nitrogen dioxide exposures in US homes nationally by ZIP code

Article Publication Date

2-Dec-2025

Biochar boosts hydrogen and methane yield in next-generation food-waste-to-energy systems

Maximum Academic Press

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By integrating biochar into semi-continuous reactors operating for 100 days, the research shows notable gains in gas yield, stronger resistance to acidification, and more resilient microbial communities.

Food waste continues to rise worldwide, placing pressure on waste-management infrastructure and increasing greenhouse gas emissions. Anaerobic digestion (AD) is widely used to convert organic waste into biogas, yet conventional one-phase digesters often struggle with poor stability, high CO₂ content, and sensitivity to microbial shifts. TPAD—which separates hydrogen and methane production—provides improved efficiency but remains limited by acid build-up and low tolerance for high organic loading rates. Chemical buffers can stabilise pH but add cost and may disrupt microbial activity. Given these challenges, exploring sustainable additives such as biochar is essential to improving TPAD performance and enabling wider industrial adoption.

A study (DOI:10.48130/een-0025-0010) published in Energy & Environment Nexus on 21 October 2025 by Yusron Sugiarto’s team, The University of Western Australia, highlights how biochar enables TPAD systems to operate at loading levels previously associated with failure, offering a practical strategy to enhance renewable gas recovery from food waste.

The study evaluated the role of biochar in a TPAD system treating food waste by operating paired semi-continuous stirred-tank reactors—with and without biochar—over 100 days across seven stages of increasing organic loading rates (0.5–6.0 g VS/(L·d)). In both the hydrogen-producing first reactor (R1) and the methane-producing second reactor (R2), the team monitored gas production rates (H₂ and CH₄), pH dynamics, volatile fatty acid (VFA) profiles, and microbial community composition to link process performance with underlying biochemical and microbial mechanisms. In R1, hydrogen production started on day 2 and increased as loading and dilution rates were adjusted, but reactors amended with biochar consistently showed higher H₂ production, with gains of 45–88% over controls and no decline even at the highest loading of 6.0 g VS/(L·d). These improvements were associated with more stable pH (≈5.5 versus 4.5–5.0 in controls) and moderated VFA accumulation, particularly reduced propionic acid build-up at high loadings. In R2, biochar likewise enhanced methane production: CH₄ appeared earlier, CH₄ content increased, and the CH₄ production rate remained stable at ~1,900 mL/d, whereas controls declined by ~12% at the highest loading as pH fell and VFAs accumulated. Throughout both phases, biochar-treated reactors maintained higher pH (around 5.5 in R1 and 7.2–7.3 in R2) and lower inhibitory VFA levels, confirming its buffering and metabolic support functions. Microbial analyses showed that biochar substantially enriched Clostridiaceae in both phases and promoted the growth of key methanogenic archaea, especially Methanosarcinaceae and Methanobacteriaceae, fostering stronger syntrophic networks and facilitating direct interspecies electron transfer. Together, these method–result linkages demonstrate that biochar stabilises semi-continuous TPAD and enables sustained hydrogen and methane production under loading conditions that destabilise conventional systems.

The findings demonstrate that biochar is a practical and cost-effective additive for stabilising TPAD systems treating food waste. By preventing acidification, enhancing microbial resilience, and enabling high-rate digestion at OLRs up to 6.0 g VS/(L·d), biochar allows TPAD systems to match or exceed the throughput of conventional anaerobic digesters while producing a higher-quality renewable gas mixture. Municipal waste facilities, agricultural biogas plants, and decentralised food-waste-to-energy systems could adopt this approach to increase renewable energy recovery, lower reliance on chemical buffers, and improve operating reliability. The study also provides a microbial basis for designing future biochar-enhanced digestion technologies.

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References

DOI

10.48130/een-0025-0010

Original Source URL

https://doi.org/10.48130/een-0025-0010

Funding information

This research received partial financial support from the Australian Research Council through the ARC Linkage Projects scheme (ARC LP100200137), the ARC Discovery Projects scheme (DP210103766 and DP220100116), and the Future Energy Export CRC (FEnEX CRC Project # 21.RP2.0059). Y Sugiarto expresses gratitude to the Directorate of Research and Community Service at Universitas Brawijaya, the EQUITY Program (Project No. 4559/2023), and the Woodman Point Wastewater Treatment Plant for supplying wastewater sludge.

About Energy & Environment Nexus

Energy & Environment Nexus is a multidisciplinary journal for communicating advances in the science, technology and engineering of energy, environment and their Nexus.

---

DOI

10.48130/een-0025-0010 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Enhancing H2 and CH4 production with biochar addition in two-phase anaerobic digestion of food waste