We welcome studies exploring all aspects of climate change in response to ambitious mitigation scenarios, including climate overshoot through scenarios that pursue net negative emissions and a reversal of global warming, and the feasibility and side effects of large-scale deployment of carbon dioxide removal. In addition to studies exploring the remaining carbon budget and the transient climate response to cumulative emissions of CO2 (TCRE), we welcome contributions on the zero emissions commitment (ZEC), effects of different forcings and feedbacks (e.g. permafrost carbon feedback), non-CO2 contributions to stringent climate change mitigation (e.g. non-CO2 greenhouse gases, and aerosols), and climate and carbon-cycle effects of carbon removal strategies, including their implications for policy. We also invite analysis focusing on consequences in a wide range of Earth System components and sectors, from ocean dynamics to the cryosphere, biodiversity and biosphere changes to human systems and economic consequences of overshoot, as well as the implications of overshoots for climate change adaptation planning.
We invite contributions that use a variety of tools, including fully coupled Earth System Models (ESMs), sectoral impact models, Integrated Assessment Models (IAMs), or Simple Climate Models (SCMs) and climate emulators. Interdisciplinary contributions from the fields of climate policy and economics focused on applications of carbon budgets, net-zero pathways, and their wider implications are also encouraged.
Orals: Mon, 4 May, 08:30–15:45 | Room 0.49/50
Methane (CH4) is the second most important anthropogenic greenhouse gas after CO2, and CH4 mitigation is a main option to limit near-term warming. Yet, the required CH4 mitigation to stay below specific temperature limits remains uncertain. Furthermore, prevalent scenarios from Integrated Assessment Models (IAMs) typically exhibit highly non-linear and correlated CO2 and CH4 emissions, due to economic optimization and aggregation of greenhouse gases (GHGs). By contrast, climate targets are often framed as linear reductions in emissions with a primary focus on mitigating CO2 emissions.
Here, we present a simple, complementary approach for scenario generation that aligns more closely with the current framing of emission targets and remains largely independent of many assumptions in IAMs. Using this scenario generation approach and the simple climate model FaIR, we systematically map peak warming resulting from a linear reduction to net zero CO2 or GHG emissions combined with different changes in CH4 emissions. We estimate that without CH4 mitigation, peak warming of 1.7 °C is already unavoidable. We provide minimum CH4 mitigation targets compatible with different peak temperatures when combined with specific net zero CO2 or GHG emission targets. We further quantify how the remaining carbon budget (RCB) depends on the stringency of CH4 mitigation. Our results show that without sizable CH4 mitigation, RCBs are far smaller than commonly communicated.
These findings emphasize both the necessity and the benefit of strong near-term CH4 mitigation, and can support policymakers in setting CH4 emission targets compatible with globally agreed-upon temperature limits.
How to cite: Weber, K., Brunner, C., Brun, L., and Knutti, R.: Peak warming and remaining carbon budgets under different methane emission targets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13648, https://doi.org/10.5194/egusphere-egu26-13648, 2026.
We are at a turning point in the history of land use: While the main purpose of land use over millennia had been food and fibre production, its huge side-effects on the Earth system became discernible. Though global land use, dominated by deforestation, was historically a driver of global warming, the potential to deploy certain land-use practices such as reforestation for climate change mitigation became evident and land-use an important part of climate policies. Understanding the interactions of land-use change and the Earth system under future climates is thus of paramount importance to ensure policy pathways are compatible with the Paris Agreement.
Historically, land-use change has profoundly depleted terrestrial carbon stocks, contributing roughly one third of historical anthropogenic CO₂ emissions. The entire land biosphere (including land-use change) has, however, acted as a major sink in recent decades, as it strongly responded to environmental changes such as rising atmospheric CO₂, which outweighed the land-use change emissions. These dual drivers – land-use changes and environmental changes – have motivated extensive efforts to quantify land–atmosphere carbon fluxes, leading to the parallel development of bookkeeping models and process-based models, which are now increasingly linked. However, once land-use change and environmental responses are considered jointly, carbon flux attribution becomes non-unique: land-use decisions and environmental change interact to generate synergistic fluxes that blur the distinction between “anthropogenic” and “natural” sources and sinks.
Here, we review the evolution and integration of land use in carbon-cycle modeling and synthesize the current understanding of land-use-environment interactions, focusing on their implications for global and national carbon budgets and future mitigation pathways. We show that synergistic effects – such as replaced and (re-)established sinks and sources – are not secondary details and discuss how recent advances have enabled a consistent treatment of these synergies in the Global Carbon Budget, while highlighting why this attribution remains, in part, a policy choice rather than a purely scientific one.
Finally, we argue that land-use–environment synergies will become increasingly consequential in the future, as land-based mitigation expands, carbon dioxide removal scales up, and climate impacts intensify. Robustly projecting the net land carbon balance will therefore require renewed attention to these interactions, supported by improved process understanding, modeling capabilities, and transparent accounting conventions. Recognizing and consistently treating land-use–environment synergies is essential for robust carbon budgeting and for assessing the effectiveness and risks of land-based climate mitigation in a rapidly changing climate.
How to cite: Pongratz, J., Schwingshackl, C., Houghton, R. A., and O'Sullivan, M.: Impacts of land-use-environment interactions on sources and sinks of CO2, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20544, https://doi.org/10.5194/egusphere-egu26-20544, 2026.
Global emissions scenarios describe the nature and pace of future transitions. As such, they have been critical to inform international policy and efforts to limit global warming to specific levels. Since the IPCC Sixth Assessment Report (AR6), the global mitigation landscape has changed substantially, yet many scenario-based benchmarks continue to rely on static assessments. The Scenario Compass Initiative (SCI) responds to this gap by providing a continuously updated, transparent, and curated collection of global emissions scenarios, combined with a systematic benchmarking framework that tracks how mitigation requirements evolve over time.
SCI introduces a novel “live” scenario collection approach that enables ongoing submission, vetting, and release of scenarios, ensuring timely access while maintaining quality control. Scenarios are assessed against feasibility and sustainability criteria, allowing the identification of a policy-relevant subset without relying on statistical outlier exclusion. Building on this curated ensemble, SCI derives benchmarks across key mitigation dimensions, including near-term emissions reductions, renewable energy deployment, net-zero timing, and reliance on net-negative emissions.
Comparing current benchmarks with those underlying AR6 reveals a marked shift in feasible mitigation pathways. The most ambitious AR6 category—characterized by immediate, steep emissions reductions and minimal temperature overshoot—has effectively become unattainable given observed emissions trends and delayed action. As a result, benchmarks for near-term mitigation, net-zero timing, and carbon dioxide removal have all shifted accordingly. At the same time, while quantitative assumptions span wide numerical ranges, most scenarios continue to rely on a narrow set of underlying socioeconomic narratives aligned with SSP1 and SSP2.
This presentation will inform about the updated benchmarks which provide critical reference points for interpreting contemporary scenarios and for supporting robust, policy-relevant climate decision-making.
How to cite: Scheifinger, K., Riahi, K., Clarke, L., Huppmann, D., Hasegawa, T., Luderer, G., Smith, C., Kriegler, E., Rogelj, J., Nicholls, Z., van Vuuren, D., van Ruijven, B., Dekker, M., Verpoort, P., Beath, H., and Sher, G.: Key Benchmarks of Global Emissions Scenarios 2025: Annual update of integrated assessment scenarios and related benchmarks for limiting global warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12960, https://doi.org/10.5194/egusphere-egu26-12960, 2026.
Reaching the Paris Agreement’s climate targets will require the large-scale deployment of Carbon Dioxide Removal (CDR), including Afforestation/Reforestation (AR). Carbon sequestration through AR is driven by plant metabolic processes affected by environmental conditions. However, AR-induced reduction of atmospheric CO2 levels causes compensating CO2 fluxes towards the atmosphere across the land and ocean. Further, beyond the CO2-induced reduction in temperature, AR also affects climate through local and non-local biogeophysical effects caused by changes in albedo, surface roughness, and transpiring leaf area. Given the breadth and interaction of Earth system effects of AR, the amount of CDR achieved depends not only on the scale and spatiotemporal pattern of the application, but also on ambient climate and CO2 levels, as determined by the emissions pathway, and complex emerging feedbacks. At the same time, understanding whether AR can cause a (non-)local warming that could potentially offset the cooling induced by the AR-driven CO2 reduction, whether this might hold across different emissions scenarios, and whether this signal can emerge from internal variability, is also crucial.
Here, using the fully coupled Earth System Model MPI-ESM, we create a multi-member ensemble of emission- and concentration-driven AR and reference simulations across different emissions pathways (SSP1-2.6, SSP5-3.4os, SSP3-7.0, SSP5-8.5). Our setup features an unprecedented number of 120 simulations in total, that allows us to robustly capture the impacts on the Earth system and the emerging climatic and carbon feedbacks across spatiotemporal scales. In the AR scenario, forest area increases by 935 Mha by 2100, representing ambitious AR in the range of country pledges (Moustakis et al. 2024).
Our results show that, under higher emissions, AR not only sequesters more carbon over land, but also does so more efficiently. In particular, for every 100 GtCO2 sequestered over land (compared to the counterfactual reference scenario), atmospheric reduction reaches 89, 85, 74, and 73 GtCO2 in SSP5-8.5, 3-7.0, 5-3.4os, and 1-2.6 respectively. The reduction of carbon sequestration due to the AR-induced reduction in atmospheric CO2 can reach 29% in SSP1-2.6, which is significantly higher than the 7% loss in SSP5-8.5. Despite AR being more efficient under higher emissions, this is not translated to gains in temperature reduction, which is not statistically significantly different between scenarios, averaging at 0.2°C globally. Overall, CO2-induced cooling dominates biogeophysically-induced warming at both global and regional scales across scenarios, whereas the isolated biogeophysical effects on temperature are insignificant at the global scale.
Our results provide robust, scenario-dependent insights into how large-scale AR works within the Earth system, and how the emerging carbon and climate feedbacks affect sequestration and temperatures across global and regional scales.
References:
Moustakis, Y., Nützel, T., Wey, HW. et al. Temperature overshoot responses to ambitious forestation in an Earth System Model. Nat Commun 15, 8235 (2024). https://doi.org/10.1038/s41467-024-52508-x
How to cite: Moustakis, Y., Nützel, T., Wey, H.-W., and Pongratz, J.: Large ESM ensemble reveals complex responses of carbon and climate feedbacks to forestation across emission pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14642, https://doi.org/10.5194/egusphere-egu26-14642, 2026.
The global ocean and terrestrial carbon dioxide (CO2) sinks have removed approximately half of the total anthropogenic carbon emissions emitted to the atmosphere since 1850. Robust estimates of future carbon uptake are paramount to determine Paris Agreement compatible remaining greenhouse gas emission budgets including negative emission pathways to balance hard to abate emissions. Missing carbon-climate feedbacks in state-of-the-art greenhouse gas concentration-driven Earth System Models (ESMs), however, render future carbon cycle estimates uncertain. Here, historical and future ocean and land carbon uptake estimates from emissions-driven CMIP6 experiments conducted with AWI-ESM-1-REcoM are presented.
In the emissions-driven model setup, carbon-climate feedbacks and differences in the initial distribution of terrestrial vegetation lead to a reduced carbon source from anthropogenic land use changes, a smaller atmospheric CO2 growth and a substantially weaker oceanic and terrestrial carbon uptake increase until the 1970s, compared to the concentration-driven model setup. Thereafter, the terrestrial CO2 sink increases stronger in the emissions-driven setup, leading to similar atmospheric CO2 growth in both model setups by the end of the historical period. In the future, ocean and land carbon sinks respond distinctively to both model setup and scenario forcing before peak emissions, between peak emissions and peak atmospheric CO2, and before and after net zero emissions. The land sink in particular continues to increase stronger than the ocean sink after peak atmospheric CO2. By the end of the 21st century, carbon-climate feedbacks yield atmospheric CO2 concentrations considerably lower by 17 to 42 ppm and a weaker ocean carbon sink in the emissions-driven model setup, with the largest differences in strong mitigation scenarios. As emissions-driven ESM setups are recommended for the upcoming CMIP7, these model results stress the need to improve our understanding of the future evolution of the global carbon sinks.
How to cite: Danek, C., Gürses, Ö., and Hauck, J.: Weaker than expected future ocean carbon uptake due to carbon-climate feedbacks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20551, https://doi.org/10.5194/egusphere-egu26-20551, 2026.
The terrestrial ecosystem is a critical carbon reservoir that faces the risk of transitioning from a carbon sink to a source under large-scale carbon dioxide removal (CDR) strategies aimed at mitigating climate change. In this study, we use a fully coupled Earth system model to simulate an abrupt decline in atmospheric CO2 concentrations from near-current levels to the pre-industrial level of approximately 280 ppm. We find that the CDR-induced reductions in net primary productivity lead terrestrial ecosystems to emit carbon. It takes approximately 14 years after removal for the global land-atmosphere system to reach a new carbon equilibrium, with recovery times varying by region, particularly delayed in the tropics. Boreal ecosystems play a key compensatory role by absorbing the excess carbon released from other regions, thereby helping to restore the global carbon balance. These findings underscore the pressing need for improved land management and a holistic approach that combines natural and technological CDR to achieve net-zero emissions targets.
How to cite: Liang, L., Liang, S., Zeng, Z., Ziegler, A., Chen, Y., Tao, Y., Jin, Y., Wang, D., Wu, T., and Zhang, D.: Response of terrestrial ecosystems carbon budget to large-scale direct CO2 removal using Community Earth System Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2101, https://doi.org/10.5194/egusphere-egu26-2101, 2026.
Despite decades of climate policy initiatives and significant advances in decarbonization efforts, global CO₂ emissions continue to rise, suggesting the influence of structural factors that counteract mitigation gains. Here, we identify financial leverage as a fundamental mechanism that underpins this persistent overshoot.
We build a stochastic macro-financial model that integrates credit dynamics, economic growth, bankruptcy risk, and cumulative carbon emissions. The model shows that growth driven by debt financing consistently increases cumulative emissions, thereby locking economies into high-carbon pathways despite reductions in emissions intensity. This arises from a double constraint: debt repayment requires sustained growth, while growth remains energy-dependent and thus generates emissions. When growth becomes increasingly dependent on leverage, financial instability and cumulative emissions rise, while gains in real wealth diminish, revealing a leverage frontier beyond which additional credit primarily generates risk.
Calibrating the model to multi-decade data for the United States, China, France, and Denmark, we find a robust coupling between debt accumulation, cumulative GDP, and cumulative emissions across distinct economic structures. These results challenge the feasibility of growth–emissions decoupling under prevailing credit-driven growth regimes and indicate that achieving net-zero targets requires aligning credit allocation with decarbonisation objectives.
How to cite: Montagnani, S., Ledoux, B., and Lacoste, D.: Debt, Growth, and the Carbon Lock-In, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11170, https://doi.org/10.5194/egusphere-egu26-11170, 2026.
Rapid reductions in greenhouse gas (GHG) concentrations are increasingly included in scenarios used to project the full range of possible future climate change, yet the response of regional climate extremes to such reductions remains highly uncertain. Here we focus on projected changes in extreme precipitation over the Northeast United States (US) in response to rapid reductions in GHG concentrations later this century. The Northeast US, the most densely populated region in North America including the Boston to Washington, D.C. metro corridor, has faced the most rapid increase in extreme precipitation events within the US over recent decades. With millions of people and critical infrastructure at risk, understanding how extreme precipitation may respond under different mitigation pathways is essential for informing urban adaptation and resilience strategies.
We use an ensemble of simulations driven by the SSP5-3.4OS scenario from the fully-coupled 25-km GFDL (Geophysical Fluid Dynamics Laboratory) SPEAR (Seamless system for Prediction and EArth system Research) model. In this overshoot scenario, hypothetical mitigation efforts are introduced starting in 2041, with net-negative GHG emissions achieved by the late 21st century. The frequency of extreme precipitation over the Northeast US increases through mid-century under rising radiative forcing but begins to decline following the sharp reductions in GHG concentrations. However, the timing of this reversal exhibits pronounced seasonality. In the warm season (May – November), extreme precipitation frequency begins to decline shortly after GHG drawdown begins. In the cold season (December – April), on the other hand, the frequency continues rising for roughly a decade after the peak global mean warming and exhibits hysteresis behavior. This delayed response in the cold season is spatially heterogeneous, suggesting that major metropolitan areas in the Northeast may experience different seasonal changes under the same climate migration efforts. These results highlight the benefit of climate mitigation in reducing extreme precipitation events, but also the complexity of regional climate responses, which can be modulated by seasonality, local-scale effects, and other factors.
How to cite: Jong, B.-T., Labe, Z., Delworth, T., and Cooke, W.: Reversal of extreme precipitation trends over the Northeast US in response to aggressive climate mitigation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5420, https://doi.org/10.5194/egusphere-egu26-5420, 2026.
Effective climate policy requires quantifying the temperature response to CO2 emissions. The current policy framework centers around Remaining Carbon Budgets, and depends heavily on there being a linear Transient Climate Response to Cumulative Emissions (TCRE) and a low Zero Emission Commitment (ZEC). The linearity of TCRE and the smallness of ZEC are based on emergent behaviors of a small number of Earth System Models (ESMs) and lack both conceptual understanding and uncertainty quantification.
Here we present an analytically tractable conceptual model for the coupled interaction of the thermal component of the climate system with the carbon cycles. Unlike previous decompositions our model is built by assembling dynamical energy balance and carbon flux models. Thus, we obtain closed-form approximations for TCRE and ZEC in terms of well-established conceptual parameters such as the radiative feedback, ocean heat uptake efficiency, the average timescale ocean carbon uptake, the Q10 temperature sensitivity of respiration, etc.
We derive conditions for both long-term (millennial-scale) low ZEC, as well as conditions for transient (centennial-scale) low ZEC, along with conditions for the near-linearity of TCRE. We find that there is no intrinsic physical reason for a low ZEC or a linear TCRE, and they arise from fortuitous compensations between unrelated parameters. We also show the system has the potential for significant centennial-scale transient amplification, arising from non-normal system dynamics.
In addition to providing conceptual insight, the model allows us to easily explore the limits of the traditional assumptions surrounding TCRE and ZEC. For example, we show that a pattern effect derived from models with observed Sea Surface Temperature patterns (AMIP), can lead to a much larger ZEC than that derived from coupled ESMs.
How to cite: Proistosescu, C., Swann, A., Armour, K., and Cael, B.: Making sense of ZEC and TCRE: A conceptual model for the coupled climate response to carbon emissions. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15838, https://doi.org/10.5194/egusphere-egu26-15838, 2026.
The Zero Emissions Commitment (ZEC) - the change in global temperature after CO2 emissions cease - plays a key role in quantifying remaining carbon budgets and assessing the reversibility of global temperature under carbon removal. ZEC has often been assumed to be close to zero in policy-relevant assessments. However, emerging single-model studies suggest that ZEC is not a fixed quantity, but may vary substantially with global warming level (GWL).
We present the first coordinated multi-model assessment of ZEC state dependence using results from the TIPMIP protocol. This analysis extends previous single-model studies by applying a consistent framework across Earth System Models (ESMs) to evaluate post-emissions temperature evolution following a common emissions-driven ramp-up to multiple GWL targets. We combine multi-century ESM simulations with a two-layer energy balance model to attribute ZEC to the evolving balance between committed ocean heat uptake warming and carbon-sink-driven cooling from land and ocean.
Preliminary intercomparisons suggest that models show relatively similar post-emissions temperature behaviour at lower GWLs (≤2K), remaining close to zero ZEC, whereas responses at higher GWLs are more varied, with most models continuing to warm. This coordinated analysis will deliver new understanding of the processes driving ZEC state dependence, with direct implications for TCRE assessments, IPCC carbon budget estimates, and the design of CO2 removal pathways.
How to cite: Gibbs, L., Jones, C., Jones, C., and Andrews, T.: State Dependence of Zero Emissions Commitment (ZEC) in Multi-Model TIPMIP Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6802, https://doi.org/10.5194/egusphere-egu26-6802, 2026.
Zero Emissions Commitment (ZEC), defined as a change in global-mean surface temperature expected to occur after net-zero CO₂ emissions, is an important factor for estimating future climate and mitigation policies.
While the carbon budget arguments predict ZEC to be zero, it actually varies between slight positive and negative values in Earth system models (ESMs) and therefore uncertainty remains. Previous studies have shown that ZEC tends to be more positive with a greater amount of cumulative CO₂ emissions, but the underlying mechanisms are not yet understood well.
To clarify them, we performed an idealized global warming experiments using MIROC-ES2L, one of the CMIP6 ESMs. The experiments consist of the so-called flat10 run (with 10PgC emission) for 1000 years and zero-emission runs branched off at the time points when global-mean surface temperature reaches different values between 2 and 8°C in flat10.
We identified that the sign and value of ZEC in MIROC-ES2L depend on the global warming level when net-zero CO₂ emission is achieved. Specifically, GSAT tends to decrease when emissions are stopped at lower warming levels, whereas it increases when emissions are stopped at higher warming levels. This behavior arises from the state dependence of the ocean heat uptake weakening and change in the effective radiative forcing associated with the carbon uptake. Using the global energy budgets, we could estimate ZEC in the equilibrium state, which was similar to the ZEC in the first 200 years after net-zero CO₂ emissions.
How to cite: Watanabe, N. and Watanabe, M.: Understanding mechanisms of the Zero Emission Commitment using MIROC-ES2L, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2709, https://doi.org/10.5194/egusphere-egu26-2709, 2026.
The ACCESS-ESM1.5 model of climate stabilisation after net-zero emissions demonstrates temperature evolution after net-zero, with significant regional variation in local mean and extreme temperature changes.
However, the extent to which changes in the magnitude of heat extremes are driven by changes in mean temperature has not previously been investigated in the stabilised net-zero model.
In analysing the relationship between mean temperature and heat extremes in this net-zero model, we find that in some regions, heat extremes do not change linearly with mean temperature. In the Antarctic and Southern Ocean regions, the mean temperature and extremes both exhibit a warming trend after net-zero, however extreme temperatures do not warm as quickly as the mean temperature. Conversely, over some land regions in the Northern Hemisphere, the mean temperature and extremes both exhibit a cooling trend, however extreme temperatures cool more quickly than mean temperatures.
By considering regional geography, we can understand the physical drivers of heat extremes including the role of sea ice and ice sheets, and understand physical limits on the temperature range of heat extremes in these regions.
How to cite: Paget, G., Zika, J., Perkins-Kirkpatrick, S., and Alexander, L.: Investigating local drivers of heat extremes in a net-zero climate model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17772, https://doi.org/10.5194/egusphere-egu26-17772, 2026.
Marine heatwaves are hazardous events particularly threatful to the ocean ecosystem. Observations show that their frequency and intensity are increasing in response to global warming. Evaluation of future marine heatwaves’ characteristics were primarily made using transient states of the Earth system. In this context, metrics were assessed at transient global warming levels (TWL), following the Paris Agreement goal to limit global warming well below 2.0°C or even 1.5°C above pre-industrial levels. However, assessment at TWL cannot be proxies for global warming stabilization storylines which require net-zero emission. In addition, current trends in global warming suggest that the Paris Agreement limits will be exceeded. Here, we analyse marine heatwaves’ characteristics at 2.0 and 4.0°C stabilized global warming levels (SWL) under net-zero and overshoot scenarios. For that, we run long term simulations following the TipMIP protocol and using the CNRM-ESM2-2 model. A positive 0.2°C.decade-1 ramp-up allows to reach the target temperatures where 300-years net-zero runs are branched. Overshoots are carried out, after 50-years of stabilization, using a symmetrical negative ramp-down. These results enable (i) to understand the global and regional evolution under net-zero and (ii) to evaluate possible hysteresis effects undergone with overshoots and net-zero pathways. In broader perspective, this work focuses on the implications for marine heatwaves’ key metrics as their consequent impacts could differ according to the pathway followed.
How to cite: Bossert, I. and Séférian, R.: Marine heatwaves under net-zero and overshoot scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11381, https://doi.org/10.5194/egusphere-egu26-11381, 2026.
The Global Monsoon Areas (GMAs), home to over half of the world's population, face escalating socio-economic risks from extreme precipitation events intensified by rising atmospheric carbon dioxide (CO2). While previous studies have examined the irreversibility of the climate system following carbon neutrality, most have focused on single carbon neutrality scenarios with limited attention to these vulnerable areas. This study assesses the irreversibility of extreme precipitation intensity across seven GMA sub-regions under eight future scenarios, incorporating four carbon neutrality targets and two reduction rates, using simulations from a state-of-the-art climate model. Our results reveal that extreme precipitation intensity exhibits irreversible behavior in response to carbon neutrality forcing, failing to return to its initial level even when atmospheric CO2 is reduced. This irreversibility is particularly pronounced when carbon neutrality timing is delayed, and the emission reduction rate is slow. Moreover, the irreversible response is nonlinear to the magnitude of carbon forcing, leading to distinct regional vulnerabilities, with some areas experiencing sharp increases in irreversibility by even small delays in reaching carbon neutrality. This region-specific behavior is largely attributed to increases in mean and variability of precipitation linked to irreversible El Niño-like warming and interhemispheric differential warming. Moisture budget analysis further shows that the intensified precipitation arises from the relative influence of thermodynamic (moisture flux) and dynamic (wind) drivers across regions. These findings highlight the urgency of rapid policy implementation in vulnerable regions and can provide a scientific basis for developing regional adaptation strategies to mitigate growing extreme precipitation risks.
How to cite: Miah, Md. B., Park, J.-Y., Lee, M.-U., Jeon, W., Byun, Y.-H., Sung, H. M., Hong, J. G., Uddin, Md. J., and Mondal, S. K.: Irreversibility of extreme precipitation intensity in global monsoon areas under multiple carbon neutrality scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8898, https://doi.org/10.5194/egusphere-egu26-8898, 2026.
Carbon dioxide removal (CDR) will be required to support rapid emission reductions and reach net zero emissions. Recent studies have highlighted different global warming impacts of CDR options depending on the durability of their carbon storage. Geological net zero, which demands that residual fossil CO2 emissions are matched by permanent geological storage of CO2, has been identified as one potential policy approach to address these durability differences, as it recognizes the warming risk of delayed CO2 release from less permanent storage. Considering the UK as a national case study, we investigate the effect a geological net zero policy may have on national climate change mitigation strategies.
Using the national-scale energy system model UK TIMES, we explore different ways of implementing a geological net zero policy: a strict implementation applied on an annual accounting basis from 2030 forward, a progressive implementation that introduces a more gradual “share” of fossil emissions covered under the policy, and a cumulative implementation to 2050 which allows emissions earlier in the time horizon to be compensated for later.
Our initial results suggest extreme difficulty in achieving GNZ, highlighting that the UK is unlikely to be able to able to reach geological net zero before 2040, as more than one decade is required to decarbonize the emitting sectors and significantly scale up removal methods with permanent storage. It is also clear that the speed of change required to achieve even this outcome is significant, requiring rapid and deep phase out of fossil fuel use much earlier than traditional scenarios suggest. We find, however, that progressive and cumulative GNZ implementations can get much closer to solving, and offer more ambitious pathways that significantly reduce the UK's cumulative emissions to 2050 compared to the current UK pathways and emissions targets. We quantify residual emissions and determine the sectors with the highest challenges for full decarbonization and find that the availability of key resource biomass as well as the pace of scaling up carbon capture and storage infrastructure have crucial impact on the feasibility of any geological net zero policy.
To our knowledge, this study is the first to assess potential geological net zero policies at national level, providing insights into the opportunities and challenges of faster decarbonization and dependence on geological carbon storage in all sectors of the UK economy. Findings of this study are also relevant for other nations considering more ambitious climate change mitigation policy.
How to cite: Broad, O., Hofbauer, V., and Butnar, I.: Geological Net Zero as policy to address the non-inequivalence of carbon emissions and removals in meeting national zero-emission targets in the United Kingdom , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12586, https://doi.org/10.5194/egusphere-egu26-12586, 2026.
The zero emissions commitment (ZEC) – change in global average temperature following a cessation of emissions – is determined by inertia in both physical and biogeochemical components of the climate system. The ZEC is commonly quantified from fully coupled model simulations in which the land and ocean respond to changes in both climate and atmospheric CO2 concentration. As a result, the role of carbon cycle feedbacks in zero emissions (ZE) simulations has not been explored in detail. This study uses an Earth system model to analyze the role of carbon cycle feedbacks in the land and ocean response to ZE. First, the model was forced with constant emissions of 10PgC yr-1 for 100 years (esm-flat10 experiment), then a series of zero emissions simulations were initialized from different time points along the esm-flat10 trajectory (esm-flat10-zec experiment). In each simulation, emissions were immediately halted, then the system was allowed to evolve. Simulations were run in fully coupled, biogeochemically coupled and radiatively coupled modes to isolate feedbacks. When the CO2 effect is isolated, atmospheric CO2 concentration declines more rapidly relative to the fully coupled mode due to continued land and ocean uptake. This decline in atmospheric CO2 concentration reduces the rate of carbon uptake, which in turn, reduces the rate of decline in atmospheric CO2 concentration. However, when the climate effect is isolated, warming results in land and ocean carbon loss. The continued warming exacerbates carbon loss, further amplifying warming. Overall, the concentration-carbon feedback acts to stabilize carbon sinks, resulting in a smaller ZEC, whereas the climate-carbon feedback acts to exacerbate carbon loss, resulting in a larger ZEC (relative to the ZEC in the fully coupled mode). Our results indicate that carbon cycle feedbacks are a key control on the ZEC, emphasizing the importance of disentangling and quantifying feedbacks in net-zero emissions pathways.
How to cite: Chimuka, R. and Zickfeld, K.: The Role of Carbon Cycle Feedbacks in the Land and Ocean Response to Zero Emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15351, https://doi.org/10.5194/egusphere-egu26-15351, 2026.
Land carbon sinks are responsible for removing about a quarter of anthropogenic CO$_2$ emissions, and make up approximately half of total global carbon sinks. Uncertainty in the response of land carbon sinks to climate and increasing CO$_2$ emissions are large, and dominate the uncertainty in total carbon sinks over the next century. Understanding the carbon cycle response to net-zero and net-negative emissions has important implications for projecting future climate. Experiments in the `flat10' model intercomparison (flat10MIP) were designed for directly estimating key climate metrics that underlie carbon budgeting frameworks. Here we characterize the response of land carbon pools and fluxes from ten emissions-driven Earth system models (ESMs) under positive, net-zero, and net-negative CO$_2$ emissions. Although there are many differences in simulated land carbon pools and fluxes across models, we find some consistent behavior across ESMs. 1) During the positive emissions phase, carbon is gained on land -primarily in vegetation pools- in both the tropics and mid-latitudes. 2) Following net-negative emissions to the point of cumulative zero emissions, vegetation carbon is lost from land. 3) In tropical latitudes, total carbon is lost coming primarily from vegetation pools, but in mid-latitudes nearly all models show net land carbon gain, primarily in soil pools. 4) Following an extended period of net-zero emissions, a majority of models again show carbon gain in mid-latitudes and vegetation carbon loss in the tropics. Under net-negative emissions the timing of vegetation carbon response relative to peak emissions is relatively consistent across ESMs, but timing of soil carbon response varies widely, implying larger intermodel disagreement associated with the longer timescale responses of land carbon.
How to cite: Swann, A., Koven, C., Proistosescu, C., Fisher, R., Sanderson, B., Brovkin, V., Jones, C., Kiang, N., Lawrence, D., Liddicoat, S., Liddy, H., Romanou, A., Steinert, N., Tjiputra, J., and Ziehn, T.: Land carbon sinks in response to zero and negative emissions across Earth system models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6030, https://doi.org/10.5194/egusphere-egu26-6030, 2026.
We analyze regional warming and extreme heat under a CO₂-overshoot pathway using eight CESM2 ensemble members forced by an emission-based experiment. The experiment prescribes a rise and decline in anthropogenic CO₂ emissions, allowing the selection of two climate states—one during overshoot and one outside overshoot—with nearly identical global emissions and global-mean surface temperature (GMST). This design provides a controlled framework to assess whether regional climate responses depend solely on the global mean state or also on the temporal sequence of forcing.
Despite matching GMST, the spatial distribution of near-surface warming differs substantially between the two states. During the overshoot period, temperatures are lower across most Northern Hemisphere land areas and higher over portions of the Southern Hemisphere compared with the non-overshoot state, producing net cooling across most global land regions. These differences are reflected in the behavior of extreme heat is generally reduced during overshoot relative to the non-overshoot state, consistent with the altered surface warming pattern.
Analysis of energy-budget components indicates that these spatial contrasts arise from asymmetric sea-ice responses between the Arctic and Antarctic. Differences in ice-sheet and sea-ice behavior modify ocean heat uptake and lead to distinct regional warming patterns under otherwise similar global forcing levels.
These results highlight that overshoot and non-overshoot climates with identical emissions and GMST can yield different regional warming and extreme-heat responses, indicating limited reversibility of regional climate impacts along overshoot pathways.
How to cite: Park, I.-H. and Yeh, S.-W.: Heatwave Differences Between Overshoot and Non-Overshoot Conditions Under Identical Emissions and Warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-718, https://doi.org/10.5194/egusphere-egu26-718, 2026.
Within the 2015 Paris Agreement, the international community committed to limiting the long-term rise of global temperature to 1.5°C. As our planet continues to heat as a result of continued greenhouse gas emissions, it has become highly likely that the world is entering a period where global mean temperatures exceed this 1.5°C limit - a period referred to as Overshoot. Despite their importance for society and policymakers, health impacts of this overshoot remain understudied, particularly the different consequences of following different overshoot pathways.
In this study we therefore combine climate model output with a well-established epidemiological model to quantify the increase of heat-related mortality under pathways that overshoot the 1.5°C target. This analysis is conducted for over 850 locations across 52 countries, for which daily city-level mortality data is available through the MCC (Multi-Country Multi-City) Collaborative Research Network. The epidemiological analysis relies on quasi-Poisson regression time series analyses and requires daily city-level mortality data to establish location specific temperature-mortality relationships. We then project heat-related mortality levels across all 540 Paris Agreement–aligned scenarios available in the IPCC AR6 Scenario Database. To this end, we estimate local heat-mortality impacts for each location as a function of global mean surface temperature, by sampling data from five fully coupled earth system model initial condition large ensembles (SMILEs). In addition, we validate our approach using bespoke earth system model simulations that represent physically consistent overshoot and stabilization pathways which follow the recently developed Adaptive Emission Reduction Approach (AERA) methodology
We find a robust linear increase of heat-mortality with the cumulative temperature exceedance above 1.5°C (“overshoot-degree-years”) of each future global mean surface temperature (GMST) scenario. Hence, both the length (time) and intensity (temperature) of the overshoot is relevant for levels of heat-mortality as the impacts scale with the integral of GMST above 1.5°C over time. The linear increase of heat-mortality is in the range of 1-2 % / °C year, with larger increases found in tropical countries. While the linear scaling is apparent in nearly all countries and within all five SMILEs used, the slope of the linear relationship depends on the SMILEs. Comparing the sampled results to the physically consistent AERA runs reveals a good agreement, although the sampling approach slightly overestimates heat-mortality after the peak of GMST. Our results thus lay an important foundation for law and policy makers, as we clearly show that delaying climate action leads to increased heat-mortality.
How to cite: Lüthi, S., Ginesta, M., Lacroix, F., Hofmann Elizondo, U., Schneidewind, T., Collaborative Research Network, M.-C. M.-C., Frölicher, T., Schleussner, C.-F., Vicedo-Cabrera, A., and Stuart-Smith, R.: Heat-mortality impacts under 1.5°C overshoot pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5472, https://doi.org/10.5194/egusphere-egu26-5472, 2026.
Most CMIP6 models simulate a substantial weakening of the Atlantic Meridional Overturning Circulation (AMOC), beginning around 1990 and persisting for decades after peak warming, with recovery requiring more than a century. This weakening is associated with reduced northward oceanic heat transport, pronounced winter cooling in the North Atlantic, a northward shift of the North Atlantic jet stream, and an increased risk of summer heatwaves in Europe, as well as a southward displacement of the Intertropical Convergence Zone (ITCZ).
While the magnitude of AMOC weakening is broadly consistent across models and scenarios, its recovery shows large inter-model differences, particularly in overshoot scenarios. Here, we investigate the reversibility of the AMOC and its impact on large-scale circulation, with a focus on temperature and precipitation and associated extreme event indices.
We analyze two Earth System Models with interactive carbon cycles (NorESM2-LM and MPI-ESM1.2-LR) under two overshoot scenarios: SSP5-3.4-OS (high overshoot) and SSP1-1.9 (low overshoot). The models exhibit contrasting AMOC responses to negative emissions. NorESM2-LM shows pronounced hysteresis and incomplete recovery, whereas MPI-ESM1.2-LR exhibits a largely reversible AMOC response with minimal path dependence. This contrast is reflected in the development of the top-of-atmosphere radiation balance, where NorESM2-LM has a pronounced hemispheric asymmetry and persistent energy imbalance during the cooling and stabilization phases, whereas MPI-ESM1.2-LR shows a largely symmetric and reversible response that closely follows global mean temperature. Results indicate the presence of Bjerknes Compensation in the northern hemisphere for NorESM2-LM, yielding a partial offset of the reduced oceanic heat transport by the atmosphere. We will further assess the reversibility of climate extremes using indices established by the Expert Team on Climate Change Detection and Indices, focusing on heat extremes, drought prevalence and precipitation intensity in regions sensitive to AMOC-induces circulation changes.
Our results highlight the central role of the AMOC in governing regional climate responses on centennial timescales and underscore the importance of understanding AMOC hysteresis and reversibility when considering the long-term consequences of delayed action and subsequent large-scale carbon dioxide removal (CDR).
How to cite: Fjeldså, J., Sanderson, B., Sandstad, M., and Gjermundsen, A.: Assessing the reversibility of temperature and precipitation extremes under AMOC weakening and recovery, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17472, https://doi.org/10.5194/egusphere-egu26-17472, 2026.
The Atlantic Meridional Overturning Circulation (AMOC), a key component of the Earth’s climate system, has long been considered vulnerable to irreversible weakening or collapse under global warming and related Greenland Ice Sheet (GrIS) melt, yet its resilience remains uncertain. Here, we use a CO2-emission-driven Earth system model with an interactive GrIS to assess AMOC reversibility under idealised CO2 emission pathways that produce near-linear global warming up to 10 K, stabilisation across 1.5-9 K, and subsequent cooling. We find that although the AMOC attains “collapsed” states by commonly used threshold definitions, these weakened states do not represent dynamical tipping: the overturning weakens quasi-linearly with global temperature increase, yet consistently and promptly recovers under cooling. In contrast, GrIS mass loss accelerates with warming, continues through stabilisations, and is only slowed by cooling, committing the planet to long-term sea-level rise. These results reveal a striking asymmetry in Earth-system resilience: under transient CO2 forcing, the AMOC strength remains dynamically reversible even under continued Greenland meltwater input, whereas the GrIS is locked into persistent decline. Our findings underscore the urgency of rapid emission cuts to limit climate overshoot, AMOC weakening, and irreversible ice-sheet loss.
How to cite: Guo, C., Yang, S., Schiller-Weiss, I., Bernales, J., Olsen, S., Koenigk, T., Mahmood, R., Tian, T., and Wyser, K.: Reversible Atlantic overturning despite continued Greenland Ice Sheet melt in global climate overshoot scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14355, https://doi.org/10.5194/egusphere-egu26-14355, 2026.
How regional climate change evolves in overshoot scenarios, in particular after the global mean temperature (GMT) peak, is not well understood. To investigate regional changes under overshoot, we develop an emulator that predicts trends in regional climate variables at the spatial level of IPCC regions from GMT time series, with applicability both before and after overshoot.
A commonly used approach to relate regional climate change to GMT is pattern scaling, which assumes a linear relationship between GMT and regional climate variables. Previous studies indicate limitations in applying pattern scaling under post-overshoot conditions, a finding that is also reflected in results produced as part of our emulator development.
We therefore apply a range of alternative techniques to solve the regional climate trend emulation problem. These include approaches based on the existing literature, such as impulse response functions and operator approximation, as well as machine-learning-based methods, including Gaussian process regression, random forests, XGBoost, state space models, and pre-trained deep-learning-based time series prediction techniques. All methods are trained on overshoot and non-overshoot simulations from CMIP6, Flat10MIP, and additional model experiments available in the literature.
We assess the performance of each approach under overshoot scenarios and compare them with simple pattern scaling used as a baseline to assess approach performance. We introduce an evaluation framework for emulations under long-term stabilisation and overshoot pathways that accounts for whether regional climate signals are reversible or irreversible and enables robust detection of overshoot and stabilisation dynamics.
How to cite: Schwind, N., Kain, V., Högner, A., Nauels, A., Nicholls, Z., Shmuel, A., Zecchetto, M., and Schleussner, C.-F.: Systematic comparison of emulation techniques for regional climate under temperature overshoot scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11739, https://doi.org/10.5194/egusphere-egu26-11739, 2026.
Due to insufficient climate action to date, the world is on track to exceed 1.5°C of global warming in the coming decade. Stringent climate action towards net zero, followed by continued net negative carbon emissions, may allow temperatures to be brought back below that level after a prolonged period of climate overshoot. Even if global mean temperatures are reversed, how such overshoot shapes regional climate patterns in the long term remains poorly understood. Here, we investigate the long-term effects of climate overshoot using explainable machine learning models to identify persistent and reversible changes in regional temperature patterns for ensembles of two different overshoot scenarios until 2300. Our approach allows for robust detection of statistically significant differences on the regional level. We address three questions: (1) which regional temperature distributions return to their pre-overshoot state, (2) which stabilize at altered conditions, and (3) how distinguishable high overshoot and low overshoot pathways remain up to 2300. To complement the machine learning analysis, we apply principal component analysis to compare pre- and post-overshoot climate states and assess their degree of convergence. Our analysis provides a methodological framework to detect climate reversibility and stabilisation on the regional level, highlighting where long-term changes persist despite global temperature decline.
How to cite: Schleussner, C.-F., Högner, A., Schwind, N., and Shmuel, A.: Detecting Regional Climate Reversibility and Stabilization After Temperature Overshoot, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11514, https://doi.org/10.5194/egusphere-egu26-11514, 2026.
Exceedance of the long-term goal of the Paris agreement to limit warming to 1.5 degree Celsius above pre-industrial levels has become inevitable due to insufficient past and present climate action. Therefore, any future scenario consistent with meeting this goal will involve some level of temperature overshoot. Thus, it is essential to understand how the Earth system responds to overshoot scenarios, how reversible these changes may be compared to non-overshoot scenarios, and what the implications could be for future generations.
Overshoot scenarios are commonly derived from Integrated Assessment Models (IAMs). These scenarios describe possible pathways of greenhouse gas and aerosol emissions, along with changes in land use. To reach a specified climate goal, each scenario relies on the deployment of various types and amounts of carbon dioxide removal (CDR), such as reforestation, bio-energy with carbon capture and sequestration (BECCS) and direct air capture (DAC). In addition to removing CO2 from the atmosphere, each of these methods is associated with distinct non-CO2 related climate effects (e.g. biogeophysical effects, emissions of non-CO2 gases).
However, most Earth system modelling studies rely on idealized CDR implementation only modelling carbon dioxide emissions or concentrations for a given scenario. This neglects the non-CO2 climate effects and feedbacks that are associated with each scenario’s CDR methods. Therefore, the objective of this research is to investigate the
To study the Earth response to overshoot scenarios, two sets of scenarios were generated using the REMIND-MAgPIE IAM, with scenarios within each set designed to meet the same cumulative CO2 emissions by 2100 (450 GtCO₂ and 650 GtCO₂). Each set includes corresponding pairs of low and high carbon budget overshoot. These scenarios achieve the defined carbon budget through different CO2 emission trajectories and portfolios of CDR methods, different policy choices affecting land-use and available CDR methods, and different levels of overshoot. The Earth system response to these scenarios is then modelled via emission driven runs using the University of Victoria Earth System Climate Model, an Earth system model of intermediate complexity.
We find that high overshoot pathways have slightly different global temperature outcomes compared to low-overshoot pathways at the time the carbon budget converges. Global mean temperature differences across scenarios range from 0.00–0.04 °C for the 450 Gt CO₂ set and 0.00–0.05 °C for the 650 Gt CO₂ set. Regionally, differences are larger and range from -0.15–0.15 °C and -0.14–0.16 °C, respectively. Cancellation of positive and negative regional temperature differences results in small differences in the global mean. Differences in temperature response across scenarios are attributed to lags in the thermal and carbon cycle response to net-negative CO2 emissions, and non-CO2 effects associated with the unique CDR portfolio within each scenario Our results highlight the importance of considering non-CO2 effects of CDR methods in Earth system models to capture the full range of Earth system responses in overshoot scenarios, particularly at regional scales.
How to cite: Harper, G., Merfort, L., Bauer, N., and Zickfeld, K.: Non-CO2 effects of carbon dioxide removal methods influence temperature response in overshoot scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15018, https://doi.org/10.5194/egusphere-egu26-15018, 2026.
Current climate policy debates increasingly refer to “overshoot” pathways; temporarily exceeding 1.5°C before returning to safe levels via net-negative emissions. Yet, this conflates geophysical recovery with socioeconomic recovery. Temperature decline does not entail that affected systems, livelihoods, settlements, institutions, recover as a result. Current literature lacks a framework for assessing when, and for whom, overshoot impacts persist as permanent legacies. This paper addresses that gap. We characterise overshoot along its three dimensions that govern system response: magnitude, duration, and rate of change. We distinguish between biophysical hazard persistence: transient hazards that recede with temperature versus persistent hazards that do not, and socioeconomic reversibility: systems that recover post-overshoot versus those that cross thresholds and do not return. Whether a socioeconomic system follows a reversible or irreversible trajectory depends on the determinants of risk: hazard characteristics combined with exposure, pre-existing societal vulnerability and response. Applying this framework to key sectors (e.g. agriculture, health, and coastal systems) we show that societal vulnerability effectively lowers the threshold for irreversibility. The same physical overshoot may constitute a manageable adaptation challenge for high-capacity systems but trigger permanent loss for vulnerable ones. Furthermore, persistent biophysical change compounds this risk by degrading the ecosystems required for carbon dioxide removal, potentially constraining the very mechanisms needed for temperature reversal. The principal danger of overshoot, we argue, lies in the accumulation of irreversible socioeconomic legacies, with direct implications for climate justice and Loss and Damage frameworks.
How to cite: Byers, E. A., Al Khourdajie, A., Pirani, A., Schleussner, C., and Stuart-Smith, R.: Climate overshoot legacy: Distinguishing transient biophysical change from irreversible socioeconomic loss, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20558, https://doi.org/10.5194/egusphere-egu26-20558, 2026.
Most pathways that meet the Paris Agreement goal of limiting the global temperature increase to well below 2 °C above preindustrial levels will require a temporary exceedance (“overshoot”) of the target temperature and subsequent restoration of the target with net negative carbon dioxide emissions. If the target temperature is exceeded, a larger proportion of frozen soils in the northern high-latitude permafrost region is expected to thaw, releasing additional carbon into the atmosphere through microbial respiration. This study investigates whether permafrost soil carbon loss during the temperature overshoot phase is reversible if the temperature is restored to its target level. To attain this goal, we force an Earth system model of intermediate complexity that includes representation of permafrost carbon processes with a set of future scenarios with varying magnitudes and durations of cumulative CO2 emissions overshoot. Results show that high-latitude soil carbon loss and recovery in response to overshoot is dependent on peak warming and the duration of time excess warming is held. Continued decline of the permafrost region soil carbon pool following restoration of the target temperature suggests that changes are irreversible for at least several centuries.
How to cite: Mihara, T., Zickfeld, K., and MacDougall, A.: Irreversibility of permafrost region carbon pool changes under temperature overshoot scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22552, https://doi.org/10.5194/egusphere-egu26-22552, 2026.
Temperature responds asymmetrically to increases versus decreases in atmospheric CO2 concentrations. Understanding this asymmetry is important for our fundamental knowledge of the climate system and for projecting temperature responses to negative emission scenarios. Here we use CESM2, a fully coupled ocean-atmosphere Earth system model, to simulate the response of temperature to a period of increasing CO2 concentrations followed by a period of prescribed decreasing concentrations. CESM2 exhibits a pronounced hemispheric contrast in temperature reversibility, with persistent warming in the Southern Hemisphere and an over-recovery of temperature in the Northern Hemisphere following CO2 removal. The Southern Hemisphere response is broadly consistent with CDRMIP simulations from other models, which similarly show that temperatures remain elevated after a reduction in CO2 concentrations. In contrast, models disagree on the sign and magnitude of temperature reversibility in the Northern Hemisphere, particularly in the high northern latitudes. This work investigates the mechanisms responsible for persistent Southern Hemisphere warming and explores the sources of inter-model disagreement in Northern Hemisphere temperature recovery. This work will help clarify the reversibility of forced temperature changes and assist in setting expectations for carbon dioxide removal strategies.
How to cite: Palmer, L. and Byrne, M.: Asymmetric Responses of Temperature to Increasing vs Decreasing CO2 Concentrations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5638, https://doi.org/10.5194/egusphere-egu26-5638, 2026.
Posters on site: Mon, 4 May, 16:15–18:00 | Hall X5
As the gap keeps widening between current greenhouse gas emissions and the ever-shrinking remaining carbon budget for achieving the Paris Agreement, there has been a surge in interest in the implementation of geoengineering proposals such as solar radiation management (SRM). However, there are ethical concerns about the governance, economic viability, and climate impacts of such measures. Our understanding of climate impacts has improved with the GeoMIP protocol and dimensions of economic viability has been evaluated in engineering cost analyses and through impact functions in cost-benefit integrated assessment models (IAM) such as DICE. Nevertheless, a critical gap remains in the modelling of SRM as a mitigation measure in multisector and dynamic analyses.
In this study, we present GCAM-SRM, a modification of the Global Change Analysis Model (GCAM 8.2). GCAM is a dynamic-recursive model with technology-rich representations of the economy, energy sector, land use, and water linked to a reduced complexity Earth system model (Hector 3.2) for exploring consequences of and responses to global to local changes and stressors. GCAM-SRM models the G6Sulfur emissions scenario with an explicit representation of a technology for stratospheric aerosol injection (SAI) with cost and resource modelling and competition with regular mitigation strategies and carbon dioxide removal measures.
The SAI technologies explicitly emit stratospheric SO2, and the Earth system model has a detailed representation of the radiative forcing due to stratospheric SO2. The Global Warming Potential (GWP) for SO2 is calculated according to IPCC guidelines to derive a CO2 equivalent for SO2, and the radiative forcing of 4.5 W/m2 corresponding to the G6Sulfur scenario is achieved by setting a global CO2e price, which acts as a subsidy for SAI technologies. We finally compare the resulting CO2e price between the G6sulfur scenario and the SSP2-4.5 scenario with no SAI. Further developments will exploit GCAM’s capabilities to model climate impacts to differentiate resource availabilty and consumption in a wamer world with and without SAI.
How to cite: Muñoz Sanchez, R., Calderon, O., Altamirano, M., Bastien-Olvera, B., and Estrada, F.: Modelling solar radiation modification in process-based integrated assessment models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15451, https://doi.org/10.5194/egusphere-egu26-15451, 2026.
Rising atmospheric CO2 enhances the land carbon (C) uptake, providing a negative feedback mechanism for atmospheric CO2. At the same time, CO2-driven warming of land and air temperature tends to weaken land carbon storage, providing a primarily positive feedback on climate (i.e. intensifying climate change). The magnitude of these effects is, beside others, mediated by the nitrogen (N) content in land, which attenuates the land C response to atmospheric CO2 and climate [Kou-Giesbrecht et al., 2025]. Comprehensive Earth System Models (ESMs) have been developed to project effects from different feedbacks on Earth’s climate change, but to date not all ESMs take into account effects from the coupled C-N cycles.
ICON is a state of the art ESM [Jungclaus et al., 2022], yet its initial land surface model (LSM) implementation JSBACHv4.3 [Schneck et al., 2022] does not include a representation of the N-cycle. Recently, the QUINCY model [Thum et al., 2019] was integrated into the ICON framework. While the geophysical processes of the initial LSM JSBACHv4.3 are taken over, the new QUINCY configuration provides an alternative representation of the vegetation and biogeochemical processes, including a more realistically representation of vegetation structure (e.g. by coupling the LAI to the available carbon) and a comprehensive representation of the terrestrial N-cycle processes.
In the current study, we apply ICON in its ICON-XPP configuration [Müller et al. 2025] and with QUINCY as configuration for ICON-Land to evaluate the N-effect on land C uptake under conditions of 1%CO2 increase in the atmosphere. For this purpose, two numerical AMIP experiments (sea surface temperature and sea ice are prescribed) were carried out for the period of 1850-2019. In one experiment only C cycle was considered, in another - C and N cycles. The modelling results will be analysed to evaluate a possible N limitation effect under the conditions of increasing atmospheric CO2.
How to cite: Nerobelov, G., Ninomiya, H., Engel, J., Gayler, V., Gong, C., Hu, P., Nabel, J., Slominska-Durdasiak, K., Schnur, R., Stacke, T., Wirth, R., and Zaehle, S.: Evaluation of N-limitation effect in 1% CO2 scenario, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23146, https://doi.org/10.5194/egusphere-egu26-23146, 2026.
India’s swift growth in energy, industry, and transportation has led to an increase in national greenhouse gas emissions by three times since 1990. This challenge is compounded by unmanaged agricultural residues and invasive species, such as Lantana camara and Prosopis juliflora, which exacerbate the deepening biomass and biodiversity crisis through the open burning of agri-biomass and the uncontrolled spread of invasive woody species, driving biodiversity loss and avoidable carbon emissions through uncontrolled decay. This study assesses the potential of utilizing and converting this “problematic biomass” into biochar as an integrated solution and scalable tool for Negative Emissions Technology (NET) in climate change mitigation, by integrating the life cycle, environmental co-benefits, and techno-economic perspectives into a single assessment framework. The comprehensive evaluation is based on thorough experimental data for these invasive feedstocks and the operational records of the commercial-scale Biochar Project, complemented by high-quality global databases from Ecoinvent and IPCC reports. The assessment synthesizes a comprehensive “cradle-to-grave” Life Cycle Assessment, adhering to ISO standards and integrated with EBC/Isometric permanence validation, within a Life Cycle Cost and Techno-Economic Assessment (LCC-TEA) framework. This further moves beyond, specifically identifying sustainable production pathways and quantifying environmental co-benefits at scale. Characterisation of feedstock reveals that the two species not only contain high amounts of carbon, due to high lignin content but also very little ash, which makes them perfect for stabilization due to the efficient conversion of biomass into stable carbon sinks through pyrolysis. Crucially, the assessment identifies logistics and the pyrolysis process energy as the primary emission hotspots in LCA, accounting for the majority of operational emissions. This framework provides a vital intervention strategy for addressing the climate crisis by bridging the gap between two key areas: ecological management and carbon markets. This provides a sustainable economic pathway, restores native biodiversity, and offers permanent and verifiable carbon removal. It also provides a practical roadmap for optimizing biochar systems, while guiding policy and investment decisions for the sustainable, large-scale deployment of invasive-biomass biochar, thereby turning an ecological liability into a climate and soil health asset.
Keywords: Carbon Dioxide Removal (CDR), Negative Emissions Technologies (NETs), Biochar, Ecological Restoration, Carbon Finance, Cradle-to-Grave Analysis, Waste-to-Value.
How to cite: Aagar, N. and Haridas Aithal, B.: Life Cycle, Environmental Co-Benefits, and Techno-Economic Assessment of Biochar Systems for Climate Change Mitigation: An Integrated Case Study from India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1344, https://doi.org/10.5194/egusphere-egu26-1344, 2026.
Marine heatwaves and biogeochemical extremes such as deoxygenation and acidification are intensifying with climate change, becoming more frequent, persistent, and spatially extensive. Of particular concern are compound events, simultaneous extremes in multiple stressors, which can interact nonlinearly and trigger severe ecosystem disruptions. While their occurrence under long-term warming is increasingly documented, much less is known about their evolution in overshooting scenarios, where global temperatures temporarily exceed the Paris Agreement’s 1.5 °C target before declining through large-scale deployment of carbon dioxide removal (CDR). Such pathways raise critical questions about whether and when marine stress conditions can return to earlier states. Here we use simulations from the Horizon Europe project RESCUE (Response of the Earth System to overshoot, climate neutrality and negative emissions), which develops pairs (overshoot vs straight-stabilization) of novel socio-economic scenarios incorporating a broad portfolio of CDR strategies and arriving at the same cumulative carbon budget by the end of the century. We assess differences in the spatial patterns, frequency, intensity, and duration of compound events between an overshoot and its respective straight-stabilization trajectory. In addition, we evaluate ecosystem exposure to cumulative stress using indices for heat, hypoxia, and acidification, defined as exposure time below ecologically dangerous thresholds for marine organisms. Our analysis focuses on the persistence of these new extreme regimes and on when and if they can be reversed.
How to cite: Bernardello, R., De Falco, C., Franco, A., Tourigny, E., and Ferrer, E.: Comparison of Compound Marine Extremes Under Overshooting vs straight-stabilization Scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11614, https://doi.org/10.5194/egusphere-egu26-11614, 2026.
Overshoot pathways involve exceeding a specific temperature target temporarily and returning to it using deliberate carbon dioxide removal methods. Quantifying the overshoot carbon budgets is becoming increasingly significant as the global mean surface air temperature approaches the 1.5°C target considered in the Paris Agreement. Contribution from non-CO2 forcings is a key component of estimating the carbon budgets. Non-CO2 forcings affect global mean temperature in two ways: i) by altering the energy balance at the top of the atmosphere (direct effect) and ii) by affecting the carbon cycle (indirect effect; for example, the effect of non-CO2 forcings on temperature causes changes in soil respiration which is a strong function of temperature). Current frameworks quantify the impact of non-CO2forcings on carbon budgets separately from CO2 forcing using emulators. Therefore, the effects of the interaction between non-CO2 forcings and carbon cycle (indirect effects) are not captured. Pre- and post-overshoot carbon budgets refer to the total anthropogenic emissions when the temperature exceeds and subsequently falls below the intended target, respectively. Here, we investigate how the indirect effects of non-CO2 forcings on global mean temperatures affect pre- and post-overshoot carbon budgets using an Earth system model of intermediate complexity.
Three sets of simulations are performed to isolate the direct and indirect effects of non-CO2 forcings on global mean surface air temperatures. The reference set involves prescribing fossil fuel emissions following historical data and Shared Socio-economic Pathways (SSP) scenarios, while excluding non-CO2 forcings. The second set (total set) involves simulations with both fossil fuel emissions and non-CO2 forcings prescribed following historical data and SSP scenarios, which simulates the total effect of non-CO2 forcings on global mean temperature. In the third set (direct set), the same non-CO2 forcings as in the total set is applied, but the atmospheric CO2 concentration is prescribed from the reference simulation. Prescribing atmospheric CO2 concentration isolates the direct effects due to non-CO2 forcings by preventing the carbon cycle feedbacks from influencing temperature. The indirect effects are calculated as the difference between total and direct sets. We find that direct warming due to non-CO2 forcing is larger at both pre-and post-overshoots compared to indirect warming. However, the relative contribution of indirect warming increases during the post-overshoot relative to the pre-overshoot because of two reasons: i) non-CO2 forcings are smaller during the post-overshoot and ii) indirect warming increases from pre- to post-overshoot because of the slow carbon cycle response to non-CO2 warming. Further, we estimate the associated reductions in pre- and post-overshoot carbon budgets due to indirect effects of non-CO2 forcings. Our results suggest that frameworks quantifying overshoot carbon budgets should assess the contributions from CO2 and non-CO2 forcings together to fully capture the effects of the interactions between non-CO2 forcings and the carbon cycle.
How to cite: Jayakrishnan, K. U. and Zickfeld, K.: Indirect Effects of Non-CO2 Forcings on Carbon Budgets in Overshoot pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14793, https://doi.org/10.5194/egusphere-egu26-14793, 2026.
Soil microorganisms play a crucial role in long-term carbon storage, with mycorrhizal fungi being one of the most studied groups due to their ecological importance. These fungi form symbiotic associations with plants, significantly enhancing biomass accumulation and promoting the uptake of atmospheric CO2, thereby increasing plant carbon assimilation. This study was conducted at the Xitou nursery (elevation 1180–1200 m) of the Experimental Forest, National Taiwan University. Taiwan spruce (Picea morrisonicola), one of key native afforestation species in Taiwan, was selected to evaluate the effects of mycorrhizal inoculation on nutrient cycling and carbon dynamics in forest soils. Measurements of soil physicochemical properties, nutrient availability, microbial composition, spruce growth performance, and biochemical traits were carried out to identify potential correlations. Microbial community analysis revealed specific taxa closely linked to improved seedling growth and increased carbon sequestration potential. Observations of phenotypic and biochemical traits across developmental stages indicated that mycorrhizal fungi regulate seedling metabolic activity. Comparative analysis between inoculated and control treatments confirmed that mycorrhizal fungi significantly influence plant physiological responses and enhance soil carbon retention. The findings support the application of native mycorrhizal inoculants in sustainable soil management and reforestation strategies to strengthen the carbon sink function of forest ecosystems.
How to cite: Chen, C.-Y., Jien, S.-H., Ko, C.-H., Lin, C.-C., Ariyawansa, H. A., Li, Z.-Y., Xu, Y.-C., and Hsiao, W.-W.: Exploring the Critical Role of Mycorrhizal Fungi in Forest Carbon Sequestration: Evidence from Taiwan Spruce, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15764, https://doi.org/10.5194/egusphere-egu26-15764, 2026.
Limiting global warming in line with the objectives of the Paris Agreement requires rapid global emission reductions. Considering current policy, it is very likely that these reductions will not be enough and that the implementation of Carbon Dioxide Removal (CDR) measures is needed in addition. Within the RESCUE project ambitious climate mitigation scenarios were designed with the same end-of-century carbon emission budgets (1150 Gt CO2 and 500 Gt CO2) with and without overshoot. This allows us to investigate potential Earth system responses to the application of different activity-driven CDR portfolios using emissions-driven Earth System Model (ESM) simulations. The CDR measures implemented in these scenarios include bioenergy with carbon capture and storage, direct air capture and storage, afforestation and reforestation, and ocean alkalinity enhancement.
Here, we present initial results from using the RESCUE scenarios in our FOCI climate model, which is one of five ESMs involved in the RESCUE project. Based on our FOCI simulations, we investigate the differences of atmospheric temperature in the overshoot and stabilization pathways to evaluate how fast climate mitigation measures are detectable in the global climate system. Acknowledging detection challenges in global ESM experiments in the context of ambitious mitigation pathways, we extend our analysis to include stratospheric temperature responses, expecting a more distinct signal-to-noise ratio compared to the troposphere.
How to cite: Bischof, S. and Mengis, N.: Atmospheric temperature response to ambitious climate mitigation scenarios from RESCUE, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18277, https://doi.org/10.5194/egusphere-egu26-18277, 2026.
The northern permafrost regions contain significant amounts of carbon and are warming at approximately 3-4 times the global rate. Understanding the response of these carbon stocks under policy-relevant overshoot scenarios is a priority for climate policy. The Illustrative Mitigation Pathways (IMPs) were policy relevant pathways in AR6 designed to limit warming to 2°C. ESM simulations are not available for these scenarios, so regional information is unavailable for these mitigation pathways.
Here, we use output from a simple climate model that has run a selection of IMPs to drive the UK land surface model JULES, with an improved and explicit representation of permafrost processes compared to the standard version used in CMIP6. Our simulations include probabilistic estimates of uncertainty in future projections derived from climate sensitivity and the spatial patterns of CMIP6 ESMs.
With the CMIP6 version of JULES, permafrost extent is reversible when global warming is reduced, even under high warming levels. However, the updated version of JULES shows a delayed recovery of permafrost extent beyond 2300 (i.e. no recovery had begun) when warming levels are reduced to 2°C. In addition, a sink-to-source transition in the northern high latitudes is more likely with explicit permafrost, and despite the temperature falling again remains a source until 2300 in many of the simulations, i.e. largely an irreversible change.
How to cite: Mathison, C., Varney, R., Hooke, D., Burke, E., Smallman, T. L., and steinert, N.: Is permafrost thaw reversible in policy-relevant overshoot scenarios? , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19913, https://doi.org/10.5194/egusphere-egu26-19913, 2026.
Limiting global warming to 1.5 °C is increasingly likely to involve temporary temperature overshoot followed by large-scale deployment of carbon dioxide removal (CDR). However, the effectiveness and reversibility of overshoot pathways remain uncertain due to climate–biosphere feedbacks and disturbance processes that may undermine net-negative emissions.
Here we present a probabilistic assessment of land-based CDR under overshoot scenarios using the reduced-complexity Earth system model OSCAR, extended with two new modules: OSCAR-Crop and OSCAR-Fire. OSCAR-Crop emulates climate–crop yield interactions for major food and bioenergy crops using Monte Carlo ensembles trained on complex crop model intercomparisons and field experiments, enabling efficient exploration of uncertainty in biomass availability for BECCS. OSCAR-Fire represents wildfire occurrence and post-fire carbon dynamics as functions of climate, vegetation, and human drivers, capturing both immediate emissions and delayed carbon losses as well as post-disturbance recovery.
We apply the fully coupled OSCAR framework to peak-and-decline pathways that temporarily exceed 1.5 °C before returning to lower warming levels through net-negative emissions. Results highlight substantial regional and probabilistic uncertainty in achievable carbon removal, driven by climate impacts on crop productivity, wildfire-induced carbon losses, and feedbacks between warming, land carbon sinks, and disturbance regimes. Our findings indicate that large-scale CDR deployment in overshoot pathways is constrained not only by socio-economic feasibility but also by nonlinear Earth system responses that may limit reversibility and increase climate risks.
How to cite: Zhu, B., Gasser, T., Liu, X., and Zhang, D.: Probabilistic assessment of land-based carbon dioxide removal and biospheric feedbacks under overshoot pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20234, https://doi.org/10.5194/egusphere-egu26-20234, 2026.
