We welcome studies exploring all aspects of climate change in response to ambitious mitigation scenarios, including scenarios that pursue net negative emissions and a reversal of global warming. 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. 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: Tue, 29 Apr | Room 0.31/32
Country-level Remaining Carbon Budgets (RCBs) can act as tools for evaluating progress in climate policy under the Paris Agreement. However, current national RCB calculations often lack comparability with National Greenhouse Gas Inventories (NGHGIs), hindering accurate assessment of Nationally Determined Contributions and progress towards emission reduction targets. Here, we developed a NGHGI-compatible methodology for calculating RCBs, revealing a significant decrease in global RCB available for allocation to countries when aligned with NGHGI accounting principles.
Our analysis further demonstrates that over 50 countries have already exceeded their fair share of the 1.5°C-compatible RCB under this NGHGI-compatible framework, when considering responsibility for historical emissions. While developed countries with lower RCBs exhibit greater emission reduction ambitions, their efforts remain minuscule compared to their accrued carbon debt.
This research is particularly relevant in light of the recent European Court of Human Rights (ECHR) ruling in the KlimaSeniorinnen vs Switzerland case, which emphasized the importance of quantifying national GHG emission limitations, including through the establishment of national carbon budgets. We aim to highlight the need for a consistent and NGHGI-compatible approach to evaluate national climate policies and take a step towards aligning national RCB assessments with the realities of national emission reporting for more accurately assessing domestic climate action on a global scale.
How to cite: Weber, K., Brunner, C., Grassi, G., and Knutti, R.: Re-evaluating progress towards climate targets with consistent national carbon budgets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5835, https://doi.org/10.5194/egusphere-egu25-5835, 2025.
In assessing responsibility for climate change, conventional metrics like cumulative and per-capita emissions do not capture the consequences of evolution of affluent lifestyles. Our study introduces a novel framework to assess the global mean surface warming that would have resulted if the historical lifestyles of individual countries had been the norm for the entire global population. We refer to the resultant warming as the carbon footprint temperature, Tcf. We find that universalising the carbon-intensive lifestyles of industrialised countries would have pushed the world beyond the 1.5°C threshold as early as the 1950s in some cases, and by the 2000s for many others, thereby risking significant destabilisation of the Earth's climate system. Our analysis concludes that the modest lifestyles of the global majority have contributed substantially to the experienced planetary stability, offering humanity a dual advantage: averting potential planetary destabilisation and providing a critical window for climate action extending from decades to a century. Accordingly, we argue that affluent entities with high carbon footprint temperatures ought to have transitioned to low or even negative emissions regimes already instead of consuming the remaining carbon space. Additionally, per capita emissions across the world need to converge to collectively self-determined levels that are well below those of current affluent lifestyles.
How to cite: Dhara, C., Jalan, S., Chakravarty, S., Bhar, S., and Seshadri, A.: The role of historic global inequality in avoided climate destabilisation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5387, https://doi.org/10.5194/egusphere-egu25-5387, 2025.
Storing carbon for centuries to millennia in geological formations will be required if the world is to achieve net-zero CO2 emissions, and an even more critical feature of mitigation strategies if net negative CO2 or net-zero greenhouse gas emissions are to be achieved in order for global mean surface temperature to decline. The technical potential for carbon storage is commonly assumed to be vast, with estimates of available storage of around 10,000-40,000 Gt CO2 in the scientific literature. We reassess that assumption, providing a new spatially explicit estimation of carbon storage potential in sedimentary basins consistent with the principle of harm prevention which can help guide policy makers when updating their climate pledges and stay within safe planetary boundaries.
We begin with current estimates of sedimentary basin volume and systematically apply a number of prudent, precautionary spatial and volumetric risk exclusions. These include minimum depths of ~1 km to ensure cap rock seal, maximum depths of ~2.5 km to avoid bedrock and limit potential seismic activation of deep rooted faults, areas with more than “moderate” historic seismic activity, environmental protection areas including the polar circles, offshore areas with >300m water depth based on current practices in the oil and gas industry, and built-up areas of human settlement under a high-population future scenario. Combining all of our risk spatial layers, we find that global storage potential declines from 11,314 Gt GO2 to 1,550 Gt CO2 of which 70% is onshore.
We classify countries into four categories combining their historical contributions to cumulative emissions and their available prudent carbon storage potential. We find that number of countries with strong per-capita contributions to historical emissions also can potentially play a strong role in storing carbon in the future (e.g., USA, Australia, Saudi Arabia) whereas others have a strong responsibility but low storage capacity (e.g., the EU) implying the need to utilize storage outside their borders.
We then compare our prudent storage potential with mitigation pathways assessed by the IPCC. We find that, if carbon storage injection rates were to be held constant at their respective levels at the time of CO2 net-zero, scenarios in line with the 1.5C limit of the Paris Agreement would allow for approximately 250 years of continued storage time, whereas scenarios with a 50% chance of limiting warming to 2C would have approximately 100 years of storage capacity remaining. However, scenarios in general tend to increase their use of storage beyond net-zero CO2 in order to counterbalance continued fossil fuel use or to draw down temperature levels beyond their peak. Extrapolating geologic storage usage forward, we find that nearly all IPCC-assessed scenarios limiting warming to 2C or less would reach our assessed planetary boundary before the year 2200.
Our analysis has broad implications for national mitigation plan development and suggests a need for countries to explicitly state their plans for geologic carbon storage as they develop the next round of their Nationally Determined Contributions.
How to cite: Gidden, M., Joshi, S., Armitage, J., Christ, A.-B., Boettcher, M., Brutschin, E., Koberle, A., Schellnhuber, H. J., Schleussner, C.-F., Riahi, K., and Rogelj, J.: A prudent planetary boundary for geological carbon storage, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-148, https://doi.org/10.5194/egusphere-egu25-148, 2025.
Under rapid global warming, changes in the climate system are increasingly evident and detectable, even for extremes and at the local scale. This, in part, has motivated countries to target achieving net zero emissions in the coming decades and to limit further global warming in line with the Paris Agreement. Climate changes under net zero emissions are projected to be substantial but may be harder to detect. It is critical that changes under net zero are well understood, both in terms of the effects of delay in emissions cessation and how these changes differ across timescales.
Here, we use a set of net zero 1000-year-long ACCESS-ESM-1.5 simulations to study the detectability of climate changes given a range of emission cessation years. We demonstrate that some local climate changes and changes in climate variability and extremes under net zero emissions may be significant enough to be detectable over human lifetimes. Some large-scale changes, especially in the cryosphere and oceans, and in the Southern Hemisphere, would be detectable within years or decades of emissions cessation. The benefits of earlier emissions cessation are also detectable even at the local scale.
This kind of analysis is not currently possible in a multi-model framework. A lack of planned coordinated net zero experiments on timescales beyond 300 years has the potential to undermine policymaking related to long-term climate changes. Using findings from the ACCESS-ESM-1.5 experiments, we demonstrate the problems that a lack of long net zero emissions simulations poses and call for coordinated 1000-year-long simulations.
We also argue that communication of ongoing climate changes under net zero emissions needs to go beyond projected global-average temperature changes (i.e. the Zero Emissions Commitment or ZEC) and emphasise other Earth System changes and local climate changes.
How to cite: King, A., Ziehn, T., Alastrué de Asenjo, E., Abram, N., Maycock, A., Borowiak, A., Clark, S., and Maher, N.: Detection and communication of climate changes under net zero emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8791, https://doi.org/10.5194/egusphere-egu25-8791, 2025.
Ongoing failure to reduce anthropogenic greenhouse gas emissions rates has fuelled debate within scientific, policy and public discourses on whether the 1.5°C high-ambition Paris Agreement goal remains within reach. The Working Group III (WG3) contribution of the Sixth Assessment of the Intergovernmental Panel on Climate Change (IPCC) report provided global mean temperature projections from 1202 integrated assessment model derived emissions pathways. Of these, 97 were deemed to be consistent with the 1.5°C Paris goal, interpreted as limiting warming to 1.5°C with no or limited overshoot. Of these 87 temporarily overshoot 1.5°C and 10 scenarios remained below 1.5°C throughout the 21st century.
However, the IPCC mitigation scenarios are rapidly becoming out of date, as most scenarios depend on rapid greenhouse gas emissions reductions after 2020 which have not occurred in reality. Furthermore, scenario warming outcomes were assessed using simple climate models calibrated in the 2010s, excluding recent observations and advances in understanding. When IPCC emissions scenarios are reharmonized to take into account recent emissions, and simple climate model calibrations are updated to incorporate recent observational constraints, no scenario in the IPCC WG3 database avoids overshooting 1.5°C, and only a handful of scenarios remain consistent with the IPCC definition of a low overshoot. This implies that the window for limiting warming to 1.5°C without overshoot has now closed.
How to cite: Smith, C., Sanderson, B., and Sandstad, M.: Updated IPCC emissions scenarios no longer limit warming to 1.5°C, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11441, https://doi.org/10.5194/egusphere-egu25-11441, 2025.
Pathways limiting global warming to well below two degrees presume the transition to low-carbon energy sources and deployment of carbon dioxide removal technologies. Among these technologies, the modeling literature consistently shows the value of direct air capture (DAC) for achieving climate stabilization in the long run. DAC offers unique advantages from a policy perspective: it is modular, less land-intensive than many comparable technologies, and enables straightforward accounting of removed emissions. However, as a novel technology, significant uncertainties remain about the barriers to scaling DAC, especially for what concerns the financial and economic viability of supporting policies and their capacity to develop DAC at scale. In this study, we explore the sensitivity of DAC deployment in an ambitious but realistic mitigation pathway (the long-term strategies committed by all major economies, or LTS) using a detailed-process Integrated Assessment Model, WITCH, across four dimensions of uncertainty: technological characteristics, financing, market requirements, and policy environments. We use recently developed probabilistic estimates to endonegize technological learning in DAC. We focus on the global level and on two time periods, namely 2025-2050, the critical moment for DAC deployment at scale, and 2050-2075, the moment where most of the net-zero goals are set. Using formal methods in statistics and sensitivity analysis, we analyze the amount of removed emissions, the energy and storage consumption, as well as the cost of the policy.
How to cite: Chiani, L., Andreoni, P., Drouet, L., Sievert, K., Schmidt, T., Steffen, B., and Tavoni, M.: Unpacking the bottlenecks of deploying Direct Air Capture at scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4158, https://doi.org/10.5194/egusphere-egu25-4158, 2025.
Achieving carbon neutrality is a great challenge, and the pathways to this goal are critical. However, it is still uncertain how the climate system will respond to different pathways for achieving carbon neutrality, including the timing of achieving the goal, whether quickly or slowly. Here, we analyze the mean and extreme climate responses under fast (SSP5-8.5) and slow (SSP1-2.6) achievement of the Paris Agreement target (2.0C), based on a linear relationship between cumulative CO2 emissions and global mean surface temperature. Results from CMIP6 multi-model simulations show a difference of about 20 years between the two scenarios, with insignificant differences in global mean surface warming between the fast scenario (SSP5-8.5) and the slow scenario (SSP1-2.6). However, there are significant regional differences, particularly in land temperature. Furthermore, these differences in achieving timing have also affected the degree of exposure to heat waves, with clear regional differences in heat wave exposure. We will discuss the physical mechanisms involved, as well as the differences in regional climate responses to extremes and averages.
How to cite: Park, I.-H. and Yeh, S.-W.: Impact of timing differences in achieving emissions targets on global heatwaves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-745, https://doi.org/10.5194/egusphere-egu25-745, 2025.
While projections of European heat extremes have been widely explored, only recent efforts address heat extremes specifically in net-zero emissions futures and with a global rather than regional focus. In addition, existing studies extend to net-zero futures spanning a few decades, but new Earth system model simulations point to substantial net-zero emissions changes over multi-centennial timescales. Therefore, we address the knowledge gap on characterising European heat extremes in long-term net-zero stabilised climates. We quantify and attribute yearly hottest temperatures (TXx) in European regions using extended Earth system model simulations with ACCESS-ESM-1.5. Analysing these 1000-year net-zero emissions simulations branched over the coming decades at different times of a transient scenario, we address the long-term effects of delayed mitigation on European heat extremes. After favourably evaluating our model for European hottest days against the ERA5 reanalysis using rank frequency analysis, we compare present-day hottest days to their long-term net-zero future likelihood. Across all European regions, any delay in achieving net-zero emissions shifts the distribution of yearly hottest days towards higher temperatures, and these extreme temperatures remain elevated for centuries. Most European regions show two- to five-fold frequency increases for heat events as strong as currently observed records, while the Mediterranean region could experience more than 30-fold increases for current records. When comparing extreme heat distributions at global mean temperature warming levels from transient periods to levels in early and late stabilised periods, we find warm shifts (about one degree) in transient climates, while colder distributions result from earlier mitigation at higher (3°C) global warming levels. We provide the first assessment of European hottest temperatures in net-zero stabilised climates, paving the way for further investigations of other extreme event types or regions in net-zero long-term timescales.
How to cite: Alastrué de Asenjo, E., King, A., and Ziehn, T.: Likelihoods of European hottest temperatures in net-zero stabilised climates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10033, https://doi.org/10.5194/egusphere-egu25-10033, 2025.
As anthropogenic greenhouse emissions continue to rise, limiting warming to 1.5°C has become elusive. Emissions pathways seeking to return to 1.5°C after overshoot will therefore require net negative emissions. A crucial question in this context is how much CO2 needs to be removed from the atmosphere to achieve a given amount of cooling (say 0.1°C). Studies seeking to answer this question often resort to the Transient Climate Response to Emissions (TCRE), a measure of the warming effect of cumulative CO2 emissions, neglecting that the climate may respond asymmetrically to CO2 emissions and removals. This contribution draws on CDRMIP pulse CO2 removal simulations to quantify the temperature response to CO2 emissions and removals in a range of Earth system models of full and intermediate complexity. We find that the temperature response to an equivalent amount of CO2 emissions and removals differs in magnitude, with the sign of this difference being model dependent. We investigate the cause for these inter-model differences by quantifying the contribution of carbon cycle and physical climate response differences to the overall temperature asymmetry. Establishing a robust metric of the transient climate response to CO2 removal is key to our understanding of how climate will respond to net negative emissions and to quantifying the amount of removal needed to restore a given temperature target.
How to cite: Zickfeld, K., Chimuka, R., and Mathesius, S.: Quantifying the transient climate response to carbon dioxide removal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14557, https://doi.org/10.5194/egusphere-egu25-14557, 2025.
Human- and nature-driven disturbances threaten the longevity of land-based carbon removal. However, even carbon that is temporarily stored still reduces global temperatures while said carbon remains stored. This temporary carbon storage can be measured in tonne-years, a metric that measures the time-integrated amount of carbon storage. Previous studies have identified two key findings: 1) that tonne-years of temporary storage are proportional to degree-years of avoided warming, and 2) that degree-years of avoided warming are proportional to climate outcomes that affect inertial components of the climate system, such as thermosteric sea level rise, ocean warming, and permafrost carbon loss. As a result, tonne-years of temporary carbon storage should also be proportional to climate outcomes influencing these inertial climate variables. Using the UVic Earth System Climate Model (UVic-ESCM), we simulate each Shared Socioeconomic Pathway (SSP) scenario, along with nine variations of each representing nine removal pathways with varying magnitudes and durations of carbon removal. Our results demonstrate that tonne-years of carbon storage are proportional to climate outcomes affecting inertial components of the climate system. This proportionality holds across a wide range of peak temperatures and temporary removal pathways, emphasizing that the impact of temporary carbon storage is path independent for some slow-responding climate variables.
How to cite: Dickau, M. and Matthews, H. D.: The proportionality between tonne-years of temporary carbon storage and inertial climate variables , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7422, https://doi.org/10.5194/egusphere-egu25-7422, 2025.
Carbon cycle feedbacks regulate the CO2 concentration in the atmosphere, with higher atmospheric CO2 levels resulting in increased uptake, and higher temperatures resulting in reduced CO2 uptake globally. Under positive emissions, the magnitude and sign of these feedbacks vary regionally. Achieving the Paris climate goals requires the use of carbon dioxide removal to reach net-zero, then enter a net-negative emissions phase, where CO2 removal exceeds CO2 emissions. The magnitude of global carbon cycle feedbacks is expected to differ under emissions and removals due to nonlinearities and state dependence of the climate-carbon cycle response. However, the magnitude of this difference (asymmetry) is poorly understood, both globally and on a regional scale. This study uses an Earth system model to investigate the regional asymmetry in land carbon cycle feedbacks under CO2 emissions and removals. To this end, two symmetric concentration-driven simulations are initialized from a state at equilibrium with twice the preindustrial CO2 concentration, with CO2 concentration increasing by 280 ppm in the “emissions” run and decreasing by an equivalent amount in the “removals” run. Each simulation is run in fully coupled, biogeochemically coupled and radiatively coupled modes to allow separate quantification of carbon cycle feedbacks. We use the Boer & Arora (2010) framework, which utilizes a carbon budget equation to compute local contributions to the global carbon cycle feedbacks, then compare these contributions under emissions and removals to determine their asymmetry. Understanding regional asymmetry in land carbon cycle feedbacks is key for determining regions likely to play a significant role in enhancing or counteracting carbon dioxide removal efforts.
How to cite: Chimuka, R. and Zickfeld, K.: Asymmetry in Regional Land Carbon Cycle Feedbacks under CO2 Emissions and Removals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15467, https://doi.org/10.5194/egusphere-egu25-15467, 2025.
Reaching the Paris Agreement’s 1.5°C climate goal will require the large-scale deployment of Carbon Dioxide Removal (CDR). Relying on single CDR methods, however, risks exceeding sustainability thresholds as compared to CDR portfolios that integrate both land- and marine-based methods. Therefore, Integrated Assessment Models have already started to include diverse CDR portfolios in modelled future pathways. While Earth System Models (ESMs) have been used to explore the climate and carbon cycle feedbacks under the deployment of individual methods, no study has yet examined the co-application of land- and marine-based CDR methods using an ESM.
Here, we use two fully coupled Earth System Models (MPI-ESM and FOCI) to investigate scaling up and/or combining land- and marine-based CDR methods under a high-emissions scenario (SSP3-7.0). Specifically, we examine the whole spectrum of Afforestation/Reforestation (AR) (0-927 Mha) and Ocean Alkalinity Enhancement (OAE) (0-16 Pmol) using a multifactorial setup encompassing seven scenarios and an ensemble of 42 simulations. The AR scenario includes ambitious forestation within the range of country pledges and has been developed based on 1,259 scenarios generated by Integrated Assessment Models, while considering biodiversity constraints and restoration potential maps. The OAE scenario includes the continuous application of alkalinity across ice-free coastline gridcells globally, with up to 16 Pmol applied – an amount sufficient to sequester as much carbon in the ocean as is the sequestration on land in the AR scenario.
Our results suggest that the efficiency of CDR, expressed as the fraction of removed carbon that remains out of the atmosphere, is ~0.85-0.87 for both AR and OAE and is independent of the magnitude of the CDR application. Overall, scaling up and/or combining the two CDR methods results in a linear scaling of carbon flux responses, despite the emerging feedbacks in the Earth system. Specifically, compared to a counterfactual no-CDR scenario, the simulated AR and OAE reduce atmospheric carbon by up to 429 and 503 GtCO2, respectively, and co-applying the two results in a reduction of 856 GtCO2. Halving the application of AR and OAE results in a reduction of atmospheric carbon by 220 and 225 GtCO2 respectively, while their combination yields 443 GtCO2.
Our findings suggest flexibility in designing CDR portfolios, as incorporating both land- and marine-based CDR methods does not compromise one or the other method’s efficiency in the two models applied. This may address sustainability concerns around large-scale deployment of single methods and can alleviate the pressure on the water-food-land nexus.
How to cite: Moustakis, Y., Wey, H.-W., Nützel, T., Oschlies, A., and Pongratz, J.: Combining and scaling up the application of terrestrial and marine CDR methods does not compromise CDR efficiency, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8318, https://doi.org/10.5194/egusphere-egu25-8318, 2025.
Assessing Earth system feedbacks arising from carbon dioxide removal (CDR) requires developing and simulating pairs of scenarios - a mitigation scenario with deployment of CDR and a corresponding no-CDR baseline. Both scenarios respect a specific long-term constraint on a carbon emission budget (i.e. emission reductions are pursued at the same level of ambition), but the latter describes a world where no CDR is deployed, such that net carbon emissions are larger and a given temperature threshold is missed. While over the past years a rich literature on deep mitigation scenarios with CDR has been emerging, the need for such no-CDR baselines has never been articulated explicitly. In idealized Earth system model (ESM) simulations of CDR, a no-CDR baseline is easy to imagine and implement, since socio-economic constraints are typically not taken into account. However, the deployment of CDR in deep mitigation scenarios, created by integrated assessment models (IAMs), is embedded in a consistent socio-economic description of plausible futures, and disallowing CDR may change many aspects of such scenarios, for example, the energy-system and land-use. Particularly, when moving towards an “activity-driven” representation of CDR in ESMs, where the activity that leads to a drawdown of CO2 is explicitly modelled (rather than prescribed by using removal fluxes from the IAM simulation), the creation of no-CDR baselines comes with challenges. Here, we conceptualize how carbon cycle and biophysical feedbacks of CDR deployment can be determined from scenario simulations and corresponding no-CDR baselines. We show that different options exist for the creation of no-CDR baselines, which offer different insights and have their specific advantages and limitations. We argue that for certain applications (e.g., the determination of regional biophysical feedbacks) the use of idealized no-CDR baselines is unavoidable to some extent, implying that we have to accept some degree of socio-economic inconsistency in no-CDR baselines.
How to cite: Schwinger, J., Merfort, L., Bauer, N., Bernardello, R., Butenschön, M., Bourgeois, T., Farooq, U., Gidden, M., Gupta, S., Lee, H., Mengis, N., Moustakis, Y., Nieradzik, L., Peano, D., Pongratz, J., Sauer, P., Tourigny, E., and Wårlind, D.: Assessing Earth system feedbacks in deep mitigation scenarios with activity-driven simulation of carbon dioxide removal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16915, https://doi.org/10.5194/egusphere-egu25-16915, 2025.
Carbon dioxide removal (CDR) strategies, such as ocean alkalinity enhancement (OAE), are crucial for limiting global warming to below 2°C alongside strong emission reductions. However, the efficiency and temperature mitigation potential of OAE under different stabilization scenarios and on long timescales remain uncertain. This study employs the Adaptive Emissions Reduction Approach within a comprehensive fully coupled Earth System Model to address these gaps. Two sets of five-member ensemble simulations spanning 1861 to 2500 were conducted: (i) stabilization scenarios at 1.5°C, 2°C, and 3°C global warming levels, and (ii) simulations applying idealized and large-scale OAE globally of 0.14Pmol per year at the ocean surface following the CDRMIP-protocol from 2026 onward using the emissions pathways from (i). Our results show that adding alkalinity at the surface lowers surface air temperature by 0.014°C per decade (1.5°C scenario) to 0.018°C per decade (3.0°C scenario). The ocean’s additional carbon uptake per unit of added alkalinity ranges from 0.53 to 0.69, with higher efficiencies in the higher global warming scenarios. However, atmospheric CO2 reduction efficiencies are up to 0.2 lower due to anomalous release of carbon from the land. OAE efficiency remains stable until atmospheric CO2 peaks but declines thereafter, driven by changes in the pCO2 equilibration timescale, which shortens with reductions in buffer capacity before peak CO2, and lengthens during the stabilization phase where buffer capacity increases again as a result of declining atmospheric CO2. These findings highlight the complex dynamics of OAE in response to evolving climate and carbon cycle feedbacks, offering critical insights for the deployment of CDR strategies.
How to cite: Grosselindemann, H., Burger, F. A., and Frölicher, T. L.: Potential of Ocean Alkalinity Enhancement in Climate Stabilization scenarios at Different Warming Levels, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6341, https://doi.org/10.5194/egusphere-egu25-6341, 2025.
99% of current anthropogenic carbon dioxide removals (CDR) happen on land, and land-based CDR such as re/afforestation or bioenergy with carbon capture and storage (BECCS) will likely play important roles on our way to net-zero/net-negative emissions while more novel methods need to be scaled up. However, the partly large estimates of the potentials of land-based CDR require a reality check, as obstacles to their implementation and non-negligible side-effects on society and ecosystems have not been comprehensively considered so far. Here, we present key results from an interdisciplinary project that scrutinized the feasibility of land-based CDR potentials at the national level of Germany and at global level applying a holistic approach to socio-ecological constraints.
Investigating the potentials for land-based CDR in Germany under different socio-economic scenarios shows that even optimistic scenarios that include extensive economic, lifestyle and dietary changes fall short of meeting both food demands and CDR requirements in line with the national LULUCF sector target. To implement CDR on a relevant scale, extensive land management and land use transitions in particular through afforestation of agricultural land are required. However, interviews with relevant stakeholders reveal diverse and extensive barriers in this regard, such as land use conflicts, changes to the landscape, knowledge gaps, limited human and financial resources and legal restrictions. Uncertainty about the political and economic future are also major obstacles, as afforestation needs a considerable investment of time before leading to economic viability. This highlights the need to assess not only the feasibility of CDR measures, but also their desirability.
Limited CDR potentials at national level draw the attention to compensating residual emissions through CDR in other parts of the world. However, CDR faces different but similarly severe constraints on global level: We not only find global land-use scenarios to be conflicting with key biodiversity areas, but [1] implementation and persistence of land-based CDR faces severe challenges by a range of socioeconomic limitations, particularly in the Global South. We find that economic and technological factors such as poverty, costs, and infrastructures are the primary constraints for successful re/afforestation across the globe, with institutional factors also being important. This provides insights into key levers for up-scaling CDR.
When comparing land-based CDR methods, as needed to inform the design of CDR portfolios, we find a lack of consistent specification of assumptions and targets in the literature. We find that the efficiency of BECCS and its advantages over conventional methods like forest-based CDR in terms of carbon storage depends strongly on the timing not just of its implementation, but even more on the world’s capacities to deliver efficient CCS. On short term, we find that re/afforestation is the more efficient CDR method across a range of vegetation models. For a complete picture, we propose to compare CDR efficiency in terms of several measures: area required, time needed to break even, and the levels of CCS and fossil-fuel substitution. Future studies should deliver explicit information on the assumed CCS and fossil-fuel substitution, which proved a major source of sensitivity of CDR estimates.
How to cite: Pongratz, J. and the STEPSEC Team: Scrutinizing the feasibility of land-based CDR potentials under socio-ecological constraints , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19740, https://doi.org/10.5194/egusphere-egu25-19740, 2025.
Climate policy aims to limit global warming by achieving net-zero greenhouse gas emissions. Climate models indicate that achieving net-zero emissions yields a nearly constant global temperature over the following decades. However, whether temperatures remain stable in the centuries after net-zero emissions is uncertain, as models produce conflicting results. Here, we explain how this disagreement arises from differing estimates of two key climate metrics, governing the carbon system’s disequilibrium and the ocean’s thermodynamics, respectively. By constraining these metrics using multiple lines of evidence, we demonstrate—with greater than 95% confidence—that global temperature anomalies decline after net-zero. In the centuries that follow net-zero, the global-mean temperature anomaly is projected to decrease by 40% (median estimate). Consequently, achieving net-zero emissions very likely halts further temperature rise, even on multi-century timescales.
How to cite: Tarshish, N., Jeevanjee, N., and Fung, I.: Cooling after net zero, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20630, https://doi.org/10.5194/egusphere-egu25-20630, 2025.
To achieve the goals of the Paris Agreement requires deep and rapid reductions in anthropogenic CO2 emissions, but uncertainty surrounds the magnitude and depth of reductions. Using the concept of TCRE—the transient climate response to cumulative carbon emissions—we can estimate the remaining carbon budget to achieve 1.5 or 2 °C. But the uncertainty is large, and this hinders the usefulness of the concept.
We are also entering an era where some of the regular metrics to monitor climate and carbon cycle change are changing if/when emissions stop increasing, begin to decline and may one day reach net zero or even globally net negative. The past behaviour of the global carbon cycle has seen a remarkably constant fraction (the airborne fraction) of CO2 emissions remain in the atmosphere each year – approximately half. But how will the Earth system behave under a new regime of decreasing and negative emissions? And is the TCRE relationship reversible – does the same gradient hold for negative emissions? We also need to understand the sequence of events which will be visible and detectable in observations of the carbon cycle if/when we achieve net zero.
Here we explore uncertainty in carbon budgets associated with a given global temperature rise as determined by the physical feedbacks in the Earth system and also by the carbon cycle response to elevated temperatures and CO2 levels. Earth system models provide a means to quantify the link from emissions to global climate change, and here we explore multi-model carbon cycle simulations across three generations of Earth system models to quantitatively assess the sources of uncertainty which propagate through to TCRE.
We examine the sequence of changes in observational metrics such as the airborne fraction and sink rate and the eventual reversal of land and ocean carbon sinks as CO2 levels decline. Quantitative understanding of this sequence is vital as we enter an era where the qualitative behaviour of the climate-carbon cycle system may be fundamentally different.
How to cite: Jones, C. and Friedlingstein, P.: Quantifying process-level uncertainty contributions to TCRE and carbon budgets for meeting Paris Agreement climate targets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17298, https://doi.org/10.5194/egusphere-egu25-17298, 2025.
This study reveals the potential of internal carbon pricing (ICP) as an essential tool for financial institutions to align their profitability goals with carbon reduction targets. The research aims to establish a practical framework for applying ICP in daily financial operations, such as loan approval processes and investment decision-making. By integrating ICP into these activities, institutions can effectively balance environmental sustainability with financial performance while advancing towards carbon reduction targets.
The implementation of ICP involves four key processes:
- Establishing internal carbon pricing : Utilizing scenario-based methodologies to calculate ICP by assessing external carbon costs and internal financial risks, providing a basis for carbon-related evaluations.
- Incorporating ICP into Carbon Management Indicators: Embedding metrics such as absolute emissions, emission intensity, and reduction pathways into operational systems to assess and manage the carbon impact of financial portfolios.
- Integrating ICP with Financial Metrics: Linking ICP with traditional indicators, such as risk-adjusted return on capital (RORAC), to assess the combined impact of carbon risks and financial returns, creating a comprehensive decision-making framework.
- Evaluating Transformation Plans: Quantifying the carbon reduction potential and financial implications of long-term business transformation strategies, factoring in projected carbon costs and benefits.
The study demonstrates that ICP can serve as a practical mechanism for financial institutions to incorporate sustainability considerations into core business operations without compromising profitability. By linking carbon pricing to both operational and financial metrics, institutions can enhance their decision-making processes and gain a competitive edge in the transition to a low-carbon economy.
How to cite: Liu, I., Tsai, T.-C., Chuang, C.-Y., Tsao, J.-H., and You, H. H.: Leveraging Internal Carbon Pricing (ICP) for Financial Institutions: A Framework for Aligning Profitability with decarbonization objectives., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4714, https://doi.org/10.5194/egusphere-egu25-4714, 2025.
The cooling sector plays a pivotal role in the global economy but significantly contributes to global warming. In 2022, cooling-related emissions accounted for 13% of global greenhouse gas (GHG) emissions. China, in particular, played a substantial role in cooling accounting for 10% of its national emissions and consuming 15% of its total electricity. This substantial environmental impact stems largely from the sector's reliance on refrigerants with high Global Warming Potential (GWP) and energy-intensive equipment. The refrigeration and air conditioning sector widely adopted hydrofluorocarbons (HFCs) as replacements for ozone-depleting substances regulated under the Montreal Protocol. However, as potent GHG, HFCs significantly contribute to global warming and are now subject to a global phase-down under the Kigali Amendment to the Montreal Protocol. Improving the energy efficiency of cooling equipment alongside the phasedown of HFCs could potentially double the mitigation benefits of the Kigali Amendment. With the growing demand for cooling in China, it is essential to explore mitigation strategies that simultaneously reduce HFC emissions and enhance energy efficiency. This study evaluates the co-benefits of efficient and climate-friendly cooling solutions in China.
This study adopts a bottom-up approach to integrate the Refrigeration and Air Conditioning - Demand, Emission, and Cost (RAC-DEC) model with Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) models. The research focuses on four key cooling subsectors: room air conditioning, mobile air conditioning, commercial air conditioning, and cold chain. The analysis is conducted under three scenarios: Business-as-Usual (BAU), reflecting current policies and practices; Kigali Amendment with enhanced energy efficiency of cooling equipment (KAE); and Accelerated Transformational Energy Efficiency (ATE). This study projects medium- and long-term trends in refrigerant and energy consumption, driven by key demand drivers for each subsector. It then quantifies both direct refrigerant emissions following the IPCC inventory methodology and indirect emissions from energy consumption. Finally, it evaluates the combined emission reduction potential under the alternative KAE and ATE scenarios.
The preliminary results indicate that among China's cooling sector, the commercial refrigeration sector offers the highest potential for emission reduction, accounting for approximately 40% of the total cumulative emission reductions from 2023 to 2060. By 2060, China’s cooling sector could achieve cumulative emission reductions of approximately 11.5 Gt CO₂-eq in the KAE scenario and 16.5 Gt CO₂-eq in the ATE scenario. In the KAE scenario, emissions are expected to decline by 48% from 2022 to 2050. In contrast, the ATE scenario predicts a 70% reduction in annual emissions, dropping from 714–721 Mt CO₂-eq in 2022 to 217–218 Mt CO₂-eq by 2050. These significant reductions are primarily driven by the accelerated phase-out of HFC refrigerants, enhanced energy efficiency, and the deep decarbonization of the power system.
This study underscores the critical role of the cooling sector in contributing to global climate goals, including the COP28 Global Cooling Pledge and the Kigali Amendment. By providing a methodological framework, our findings offer essential scientific support for policymakers in China and beyond, facilitating coordinated efforts to actively reduce fluorinated GHGs and enhance energy efficiency within the cooling sector.
How to cite: Jiang, P., Purohit, P., Bai, F., Xiang, X., Chen, Z., and Hu, J.: Co-benefits of efficient and climate friendly cooling in China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6848, https://doi.org/10.5194/egusphere-egu25-6848, 2025.
Background: Biodiversity loss is expected to escalate with every increment of additional global warming. At the same time, land-intensive climate change mitigation strategies, such as afforestation and bioenergy (with or without carbon capture and storage), may further compound biodiversity loss. This duality of drivers of biodiversity loss in the context of climate change raises the question of how these drivers compare in terms of magnitude.
Objective: By combining spatial data on biodiversity refugia with spatial time series data on bioenergy crop plantations and afforestation for multiple scenarios with varying levels of climate action and overshoot, we compare land use-related and warming-related pressure on today’s biodiversity refugia. We evaluate different biodiversity recovery assumptions when returning from a temporary temperature overshoot, compare impacts across climatic zones, and explore differences between three different models, namely, AIM, GCAM, GLOBIOM, and IMAGE.
Preliminary results: We show how scenarios with more ambitious temperature outcomes result in higher potential land pressure on today’s biodiversity refugia areas as more land-intensive mitigation options are implied. Meanwhile, more decisive climate action, including more land-intensive mitigation options, substantially reduces the warming-related loss of today’s biodiversity refugia areas. Based on our analysis, we find that refugia loss due to warming is larger than refugia loss due to land-intensive mitigation if we assume no refugia recovery after peak warming. However, this changes towards the end of this century if we assume that temporarily lost refugia can be recovered and repopulated when returning from a temporary temperature overshoot.
How to cite: Prütz, R., Rogelj, J., Price, J., Warren, R., Forstenhäusler, N., Wu, Y., Derci Augustynczik, A. L., Wögerer, M., Krisztin, T., Havlík, P., Kraxner, F., Frank, S., Hasegawa, T., Doelman, J., Daioglou, V., and Fuss, S.: Warming versus land-intensive mitigation impact on biodiversity refugia across climate policy scenarios, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9028, https://doi.org/10.5194/egusphere-egu25-9028, 2025.
Most Marine Carbon Dioxide Removal (mCDR) methods rely on creating a deficit in seawater CO₂ concentrations and partial pressure (pCO₂), quantified as a deficit in dissolved inorganic carbon (DIC). This DIC deficit drives atmospheric CO₂ uptake or reduces CO₂ outgassing.
The success of mCDR depends on efficient air-sea CO₂ equilibration before the DIC deficit becomes isolated from the atmosphere through water mass subduction. Since equilibration spans vast ocean regions, in situ measurements are impractical, making numerical modeling essential.
This study utilizes the ACCESS-OM2 model at three resolutions (0.1°, 0.25°, and 1°) to investigate how equilibration timescales vary with resolution, ranging from non-eddying to eddy-rich. Inter-model comparisons with CESM2 and ECCO indicate that model resolution has limited impact in the tropics but a stronger influence in polar regions. Furthermore, intra-model differences (due to resolution) are smaller than inter-model differences.
To improve accessibility, we introduce a computationally inexpensive virtual particle tracking method. This innovative approach offers a low-cost alternative to traditional, HPC-dependent ocean modeling, enabling easier testing of air-sea equilibration timescales, particularly for non-specialists.
These findings advance model-based assessments of air-sea CO₂ equilibration timescales and provide a practical, accessible tool for enhancing mCDR effectiveness.
How to cite: Xie, Y., Spence, P., Corney, S., and Bach, L.: Advancing Ocean Modelling Tools to Constrain Marine CDR Effectiveness by Testing Air-Sea Equilibration Timescales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10172, https://doi.org/10.5194/egusphere-egu25-10172, 2025.
Carbon Dioxide Removal (CDR) encompasses a wide range of anthropogenic activities to remove CO2 from the atmosphere to reduce its climate warming effect. The implementation of CDR technologies is necessary to achieve global climate-temperature goals. Commonly, negative emissions effects on the climate and carbon cycle have been thought to be nearly equal but opposite to those of positive emissions. This assumption was challenged recently, with results showing an asymmetric response of the Earth system to positive and negative emissions over a 1000-year timescale (Zickfeld et al. 2021). Positive emissions showed a more potent effect at increasing atmospheric CO2 concentration than negative emissions at reducing it. Yet, positive emissions had a less potent effect at increasing atmospheric temperature than negative emissions at decreasing it. Here we aim to re-evaluate the asymmetric climate-carbon response of the Earth system to negative emissions in a shorter-immediate timescale using an emissions-driven approach. Starting from a preindustrial spin-up the University of Victoria Earth system climate model (version 2.10) was forced with 10 PgC/yr emitted to the atmosphere until the cumulative carbon emission budget reached 1000 PgC (esmflat-10-1000PgC). Thereafter, pulses of positive and negative CO2 emissions ranging from ±50 to ±750 PgC were emitted or removed instantly. To assess the transient climate response to cumulative negative CO2 emissions a -10 PgC/yr was carried. Finally, a zero emission simulation from pre-industrial served as a control. Our results show agreement with the temperature and carbon asymmetry shown in previous studies. However, we only observed relative large differences with regards to atmospheric temperature and carbon redistribution in the first 40 years of simulations. Later responses (>50 years) show much small differences between the mirrored atmospheric CO2 concentrations and temperatures to negative and positive emissions. The transient climate response to cumulative CO2 emissions and cumulative CO2 removal was found to be 1.81 and -1.79 K/EgC, respectively. These findings suggest that, while temperature asymmetry may remain undetectable in the first century of negative emissions deployment, carbon cycle dynamics could deviate significantly from symmetric assumptions. This highlights the importance of accounting for asymmetric carbon redistribution when designing negative emission strategies.
References:
Zickfeld, K., Azevedo, D., Mathesius, S. et al. Asymmetry in the climate–carbon cycle response to positive and negative CO2 emissions. Nat. Clim. Chang. 11, 613–617 (2021). https://doi.org/10.1038/s41558-021-01061-2
How to cite: De Sisto, M., Hohn, D., and Mengis, N.: Earth system climate-carbon response to pulses and continuous negative emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10673, https://doi.org/10.5194/egusphere-egu25-10673, 2025.
Achieving global climate goals requires heightened ambition and innovative measures. Banks of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), potent non-CO2 greenhouse gases, represent a significant yet untapped mitigation opportunity. Globally, fluorocarbon refrigerant banks are estimated at 24 Gt CO2-eq and continue to grow, forming a massive and expanding reservoir of greenhouse gases that will eventually be released into the atmosphere if left unaddressed. While the Montreal Protocol and its Kigali Amendment regulate the production and consumption of fluorocarbons, emissions from existing stocks remain largely unregulated. Fluorocarbon lifecycle management (FLM) – encompassing leakage prevention, recovery, recycling, reclamation and destruction – presents a viable solution to mitigate these emissions. In China, the world’s largest producer and consumer of HCFCs and HFCs, implementing FLM could unlock substantial mitigation potential beyond current climate action, serving as a critical step toward net-zero goals. This study provides the necessary systematic evaluation to harness this opportunity.
To comprehensively assess the emission profiles of banked fluorocarbons with or without FLM, we developed the Extended Lifecycle Emissions Framework (ELEF), a refined emission modeling approach rooted in IPCC methodologies. ELEF expands conventional frameworks to cover both direct and indirect emissions across the entire lifecycle of fluorocarbons in equipment/product. A bottom-up cost analysis, adapted from the widely applied Greenhouse gas and Air pollution Interactions and Synergies (GAINS) framework to capture sector- and substance-specific treatment nuances, was conducted to assess the cost-effectiveness of FLM in China. Leveraging detailed activity data and localized emission factors, we reconstructed the country’s fluorocarbon banks and emissions from 2000 and projected them through 2060. Mitigation potential was then quantified across varying ambition levels defined by abatement cost cap, with climate impacts assessed using impulse response functions (IRFs) that incorporate climate-carbon feedback.
Our results reveal that China currently holds 3.6 ± 0.1 Gt CO2-eq of fluorocarbon banks, which are projected to peak at 4.5 ± 0.1 Gt CO2-eq by 2034. If unmanaged, emissions from these banks could contribute an additional 0.014℃ to global warming by mid-century. FLM, however, could prevent up to 8.0 Gt CO2-eq of cumulative emissions by 2060, reducing the peak temperature increase contribution by 62.4%. Notably, 57 out of 76 mitigation options analyzed exhibit average abatement costs below 10 USD/t CO2-eq, enabling 93.2% of the maximum mitigation potential at a total cost of 18.9 billion USD. These cost-effective measures could deliver additional mitigation equivalent to over 50% of the 13 Gt CO2-eq reductions pledged under the Kigali Amendment in China, or reduce the surface warming contribution of global HFC emissions in 2050 by more than 10%.
This study introduces a robust framework for assessing the costs and benefits of FLM. By applying it to China, we demonstrate the significant mitigation scale and feasibility of national-level implementation. Our findings highlight the substantial and cost-effective climate benefits achievable through FLM, offering policymakers an actionable pathway to bridge the emission gap and echoing recent international calls for immediate action.
How to cite: Chen, Z., Purohit, P., Bai, F., Gasser, T., He, Y., Höglund-Isaksson, L., Jiang, P., and Hu, J.: Cost-effective climate benefits through fluorocarbon lifecycle management in China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10845, https://doi.org/10.5194/egusphere-egu25-10845, 2025.
Intact land and freshwater ecosystems are a prerequisite for limiting global warming in accordance with the Paris Agreement. However, the critical co-dependence of climate mitigation outcomes and freshwater dynamics tends to be neglected in both research and policies. Here, we suggest a framework for systematically quantifying the indispensable freshwater requirements for mitigation measures, focused on natural and managed terrestrial systems upholding the land carbon sink. We assert that while huge freshwater volumes are involved in this biospheric service per se, a substantial fraction of these volumes and their spatial connectivity need to remain inside a certain variability corridor in order to maintain the current mitigation potential and to enable measures creating further ‘negative emissions’. Moreover, we highlight that the freshwater volumes and flows required are limited both by the equally substantial water requirements for other societal goals such as food security and by the potential resilience loss due to aggravating impacts of ongoing climate change. In view of high uncertainties and knowledge gaps regarding the underlying processes and feedbacks, coordinated inter- and transdisciplinary research is needed to comprehensively assess global freshwater flows and uses with explicit consideration of water-resilient climate mitigation.
How to cite: Wang-Erlandsson, L., Stenzel, F., Gerten, D., Seaby Andersen, L., Porkka, M., Wiersma, L., Lundberg Ingemarsson, M., and Rockström, J.: Critical freshwater requirements for meeting the Paris Agreement, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15423, https://doi.org/10.5194/egusphere-egu25-15423, 2025.
Exceeding atmospheric CO2 concentration of 350ppm for extended periods risks triggering climate tipping cascades, including permafrost thaw, ice sheet collapse, and ecosystem diebacks (Armstrong McKay et al., 2022). To prevent these irreversible changes, it is crucial to urgently bind at least 400 Gt of carbon from the atmosphere (Desing, 2022). Capturing CO2 and disposing it in the Earth’s crust under pressure carries uncertainties regarding long-term storage stability and potential leakage back into the atmosphere (Vica et al., 2018). Additionally, such methods lack economic incentives. Therefore, capturing CO2 and processing it into more stable carbon-dense solid materials that can be used in industrial applications offers both a solution to prevent leakage and an economic incentive.
Mining the Atmosphere (MtA) technologies provide a pathway to achieve this by capturing CO2 and converting it into high-value, long-term carbon-based products (Lura et al., 2025). To assess the scalability and sustainability of such processes, we develop a comprehensive model to optimize CO2 capture and conversion to minimize minimising grey and operational energy demand. We exemplify the approach on conversion to methane, and methane pyrolysis, with the resulting graphite bound in concrete. The model incorporates temporal and spatial differences in solar energy availability as well as local demand for C-based products. Two key scenarios are explored: in the first, MtA process are localized to meet local demand, operating when excess renewable energy is available. In the second, CO2 capture and methanation occur in solar-rich regions (e.g., deserts), with methane transported to solar-constrained regions (e.g., high latitude areas) for pyrolysis to provide carbon for concrete and hydrogen for energy supply.
By integrating material and energy dynamics, our model provides actionable insights for scaling MtA technologies to capture and store CO2 at multiple Gt/a scale. This aligns with planetary boundaries, minimizes the risk of tipping cascades, and enables long-term, economic-incentivised, decentralized carbon storage. Our work highlights MtA as a vital strategy to mitigate climate change and transition towards a carbon-neutral socio-economic metabolism.
Armstrong McKay, D.I., Staal, A., Abrams, J.F., Winkelmann, R., Sakschewski, B., Loriani, S., Fetzer, I., Cornell, S.E., Rockstrom, J., Lenton, T.M., 2022. Exceeding 1.5 degrees C global warming could trigger multiple climate tipping points. Science 377 (6611), eabn7950. https://doi.org/10.1126/science.abn7950.
Desing, H., Widmer, R., 2022. How much energy storage can we afford? On the need for a sunflower society, aligning demand with renewable supply. Biophys. Econ. Sust. 7 (3), 3. https://doi.org/10.1007/s41247-022-00097-y.
Lura, P., Lunati, I., Desing, H., Heuberger, M., Bach, C., & Richner, P. 2025. Mining the atmosphere: A concrete solution to global warming. Resour. Conserv. Recycl. 212, 107968-. https://doi.org/10.1016/j.resconrec.2024.107968
Vinca, A., Emmerling, J., Tavoni, M., 2018. Bearing the cost of stored carbon leakage. Front. Energy Res. 6. https://doi.org/10.3389/fenrg.2018.00040.
How to cite: Vingerhoets, R. and Desing, H.: A spatiotemporal modelling framework for Mining the Atmosphere: a scalable pathway to mitigate climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18437, https://doi.org/10.5194/egusphere-egu25-18437, 2025.
To achieve the goals of the Paris Agreement, the European Union and Germany have committed to achieving net-zero greenhouse gas emissions by 2050 and 2045, respectively. This requires not only drastically reducing emissions but also scaling up Carbon Dioxide Removal (CDR) deployment and infrastructure. Large-scale implementation of CDR involves challenges related to feasibility (technological viability, resource availability, legal compliance, political feasibility) and fairness (inclusive decision-making, transparent communication), while the CDR deployment impacts individuals, society, the environment, and the ratio and distribution of these impacts. To enable legitimate, fair, and widely supported decision-making on the scaling-up process, a comprehensive framework is needed that compares CDR measures and additionally evaluates their trade-offs with other sustainability goals, necessitating transparent assessments of both, implementation processes and outcomes.
Existing assessments of CDR either analyze CDR methods or portfolios without considering the socio-economic context or focus on future scenarios that only cover a small set of CDR methods due to missing method implementation in the models. To address these gaps, we developed the CDRterra assessment framework (AF) and an ambitious, plausible future CDR scenario for Germany to which the AF is applied to. All works are part of the interdisciplinary CDRterra research program involving around 100 researchers who contributed to workshops, including stakeholder groups and colleagues from the partner program CDRmare to design the scenario and develop the AF.
The scenario is based on the SSP2 aligned with Germany's climate policies and combines cost-optimization and agent-based models, ex-post assumptions, and bottom-up calculations. It considers land, biomass, energy, and CO₂ transport and storage capacities in Germany to derive consistent deployment targets for nine CDR methods: afforestation/reforestation and forest management, agroforestry, cover cropping, BECCS, DACCS, PyCCS, enhanced rock weathering, artificial photosynthesis, and CO₂-negative building materials. Results indicate potential annual removal of 1-40 MtCO₂ per method by 2045.
We applied the CDRterra AF to the CDR measures of this scenario for the years 2030, 2045, and 2060, and evaluate both, the process and impact of such a large-scale CDR implementation which is embedded in a future socio-economic context, described by e.g., energy and biomass demand and supply, economic growth, and societal behavior. The data to fill the AF was generated by the research process within CDRterra. The structure of the AF itself builds on existing frameworks (esp. IPCC and German-specific assessment frameworks) but introduces key innovations: a clear distinction between feasibility and desirability, and between descriptive information and its normative assessment. The descriptive level is based on a data base of 120 variables, informing 90 indicators. The indicators are evaluated according to the 18 assessment criteria linked to societal norms, policy goals, and ethical considerations.
By applying the CDRterra AF to the German CDRterra scenario, we evaluated large-scale CDR implementation and identified key risks, benefits, barriers, and leverage points for each CDR method. This analysis provides a transparent knowledge base to inform societal debates and support evidence-based climate policy decisions on CDR deployment.
How to cite: Havermann, F., Dorndorf, T., Holland-Cunz, A., Moustakis, Y., Strefler, J., Karstens, K., Haas, T., Wey, H., Schenuit, F., Voigt, L., Baatz, C., Kriegler, E., Oschlies, A., and Pongratz, J.: Scaling Carbon Dioxide Removal in Germany: Insights from the CDRterra Framework and Scenario, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19617, https://doi.org/10.5194/egusphere-egu25-19617, 2025.
Meeting the Paris Agreements’ climate target will require the large-scale deployment of Carbon Dioxide Removal (CDR) methods. Afforestation/reforestation (A/R) has been widely practiced and constitutes virtually all of CDR applied so far. However, implementing large scale A/R strongly depends on biophysical conditions and socioeconomic contexts defining the likelihood for implementation as well as maintenance of an A/R project. To date, biophysical enabling and constraining conditions have been extensively investigated, but studies on socioeconomic determinants remain largely confined to local scales and are primarily in the forms of qualitative evaluations. Hence, we lack a unified global understanding of socio-economic factors that have determined A/R success so far, despite the large potential of drawing on the growing database of global spatially explicit socioeconomic dimensions for a more comprehensive assessment. Here, we use machine learning to leverage multiple data streams and to explore why some countries succeed in A/R efforts while others fall short. We show that a country is likely to achieve better A/R outcomes (both in terms of absolute area and ratio of planted forest) when it has lower poverty rate, lower relative implementation cost and lower food insecurity, as well as strong institutions, adequate infrastructure and social acceptance of A/R. Economic factors (poverty, food security, implementation cost, forest road and workforce) play a key role in predicting A/R outcomes (accounting for ~70% of the relative importance), and institutional factors (governance and land tenure) contribute around 20%, while social factors (social acceptance and land use decision making) contribute only marginally (~10% ). Our analysis revealed that a considerable number of countries–particularly in tropical regions–have significant potential but simultaneously face multiple socioeconomic constraints to upscaling implementation and maintaining the carbon sink. Our findings suggest that the A/R-based CDR potential could be overestimated when such socioeconomic barriers are not considered. This is likely the case in future scenarios generated by Integrated Assessment Models, as they typically do not explicitly consider many social, institutional and ethics-related factors. Our results suggest key entry points for effective mitigation policy that alleviates socioeconomic barriers, in particular via fighting poverty. Our study complements the extensive literature base on biophysical constraints to CDR by a unique compilation of the existing global datasets on socioeconomic determinants. This provides a vastly expanded basis of factors that can be considered when assessing the implementation likelihood and permanence of A/R and can guide the design of pathways that not only operate within safe socioeconomic boundaries, but also realizes the biophysical potential of CO2 removal.
How to cite: Bao, W., Obermeier, W., Moustakis, Y., Garschagen, M., and Pongratz, J.: Socioeconomic determinants of re/afforestation efforts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19796, https://doi.org/10.5194/egusphere-egu25-19796, 2025.
Carbon budgets are quantifications of the total amount of carbon dioxide that can ever be emitted while keeping global warming below specific temperature limits. They are widely used to interpret and inform climate change mitigation actions, be it by countries or corporates. Estimates of these budgets for limiting warming to 1.5 °C and well-below 2 °C include assumptions about how much warming can be expected from non-CO2 emissions. These assumptions, however, are often poorly understood by users of carbon budget information. In this study, we clarify the non-CO2 emissions assumptions that underlie the remaining carbon budget estimates by the Intergovernmental Panel on Climate Change and quantify the implication of the world pursuing alternative higher or lower non-CO2 emissions trajectories. We consider contributions of methane, nitrous oxide, fluorinated gases, and aerosols and show how pursuing inadequate methane emission reductions causes remaining carbon budgets compatible with the Paris Agreement temperature limits to be exhausted today. A decision not to reduce non-CO2 emissions hence effectively puts the achievement of the Paris Agreement out of reach.
How to cite: Rogelj, J. and Lamboll, R. D.: The carbon budget might be smaller than you think: non-CO2 contributions to the quantification of remaining carbon budgets in line with the Paris Agreement, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21101, https://doi.org/10.5194/egusphere-egu25-21101, 2025.
