Elmar Kriegler’s research while affiliated with Universität Potsdam and other places

Net-zero commitments have become the focal point for countries to communicate long-term climate targets. However, to this point it is not clear to what extent conventional emissions reductions and carbon dioxide removal (CDR) will contribute to net-zero. An integrated market for emissions and removals with a uniform carbon price delivers the economically efficient contribution of CDR to net-zero. Yet it might not fully internalise sustainability risks of CDR and hence could lead to its overuse. In this study, we explore the implications of separating targets for emissions and for removals delivered by novel CDR in global net-zero emissions pathways with the Integrated Assessment Model REMIND. We find that overall efficiency losses induced by such separation are moderate. Furthermore, limiting the CDR target comes with increasing emission prices but also significant benefits: lower cumulative emissions, a lower financial burden for public finance of CDR and limited reliance on geologic CO2 storage but fails to lower the biomass demand. Proposed targets should also ensure sufficient CDR deployment to achieve net-negative emissions in the second half of the 21st century.

Integrated assessment models (IAMs) are crucial for climate policymaking, offering climate mitigation scenarios and contributing to IPCC assessments. However, IAMs face criticism for lack of transparency and poor capture of recent technology diffusion and dynamics. We introduce the Potsdam Integrated Assessment Modeling validation tool, piamValidation, an open-source R package for validating IAM scenarios. The piamValidation tool enables systematic comparisons of variables from extensive IAM datasets against historical data and feasibility bounds, or across scenarios and models. This functionality is particularly valuable for harmonizing scenarios across multiple IAMs. Moreover, the tool facilitates the systematic comparison of near-term technology dynamics with external observational data, including historical trends, near-term developments, and stylized facts. We apply the tool to the integrated assessment model REMIND for near-term technology trend validation, demonstrating its potential to enhance transparency and reliability of IAMs.

Social and environmental agendas are intricately connected and shape the international policy discourse. To support these discussions, we present a framework for interpreting global scenario outcomes on energy demand and supply-side transitions through the lens of societal well-being and minimum resource requirements. We develop and apply a new model called Decent living standards and the Environment in Scenarios considering Inequality and Resource Efficiency (DESIRE) to fill a critical gap in modelling inequality-growth-efficiency interactions. Utilising bottom–up literature on energy inequality and minimum energy requirements, we analyse system-wide changes from integrated assessment models to assess whether levels of energy consumption in pathways can be consistent with providing decent living standards (DLS) for all, covering three sectors in 173 countries. We apply DESIRE to multiple new sustainable development pathways (SDPs). By 2040, the combination of ambitious inequality reductions, service provisioning efficiency, and higher energy services in the SDPs reduces the global residential and commercial energy deprivation—currently over 5 billion people—by at least 90%. Industry energy gaps are closed, but transport gaps remain. In the SDPs, more than half of the global population—including in low-income countries—achieve living standards more than twice as high as the DLS benchmark for the residential and commercial sector. Energy use beyond DLS across all sectors accounts for about two-thirds of total energy use globally. Efficiency improvements reduce global energy requirements 30%–46% by 2040 in the SDPs (across countries from 17–35 GJ cap⁻¹ in 2020 to 9–23 GJ cap⁻¹), while climate policies reduce CO2 emissions related to energy for DLS to almost zero in 2050, keeping cumulative emissions for DLS for all until 2050 close to the size of the remaining carbon budget to 1.5 °C (at 50% probability). This work illustrates the possibility of pathways that deliver DLS for all while meeting the Paris Agreement.

Scenarios represent a critical tool in climate change analysis, enabling the exploration of future evolution of the climate system, climate impacts, and the human system (including mitigation and adaptation actions). This paper describes the scenario framework for ScenarioMIP as part of CMIP7. The design process, initiated in June 2023, has involved various rounds of interaction with the research community and user groups at large. The proposal covers a set of scenarios exploring high levels of climate change (to explore high-end climate risks), medium levels of climate change (anchored to current policy action), and low levels of climate change (aligned with current international agreements). These scenarios follow very different trajectories in terms of emissions, with some likely to experience peaks and subsequent declines in greenhouse gas concentrations. An important innovation is that most scenarios are intended to be run, if possible, in emission-driven mode, providing a better representation of the earth system uncertainty space. The proposal also includes plans for long-term extensions (up to 2500 AD) to study slow climate change-related processes, and (ir)reversibility. This proposal forms the basis for further implementation of the framework in terms of the derivation of climate forcing pathways for use by earth system models and additional variants for adaptation and mitigation studies.

The Paris Agreement on climate change and the 2030 Agenda on Sustainable Development require unprecedented transformations to sustainability, while maximising synergies and minimising trade-offs between the two agendas. The policy studies and sustainability transition literatures suggest that addressing the complex policy interlinkages requires ambitious, coherent, comprehensive and credible policy mixes supported by synergistic combinations of governance modes. We investigate to which extent these assumptions are reflected in quantitative scenarios produced with integrated assessment models. As a case study, we assess a new set of target-seeking sustainable development pathway (SDP) scenarios. We scrutinise the modelling protocols and the scenario results to analyse the extent to which these modelled SDPs represent governance modes and policy instrument types and purposes, and assess the resulting policy mix characteristics. As such, we bridge the scenario modelling and policy mix literatures and provide an initial pathway appraisal. We find that the modelled SDPs use policy mixes to constrain negative side-effects of unmitigated climate measures to achieve several SDGs simultaneously. The policy mixes speak to several policy mix characteristics. However, they are only partially spelled so far and their credibility remains limited. This calls for additional policy-translation efforts.

The future of food and land systems is crucial for achieving multiple UN Sustainable Development Goals, given their essential role in providing adequate nutrition and their significant impact on Earth system processes. Despite widespread consensus on the need for transformation, discussed strategies vary widely, from technology-driven to sufficiency-focused approaches, emphasizing different agents of change and policy mixes. This study assesses the implications of a new generation of target-seeking scenarios incorporating such diverse sustainability perspectives. We apply two integrated assessment models to explore food and land futures under three whole-economy sustainable development pathways (SDPs): Economy-driven Innovation, Resilient Communities, and Managing the Global Commons. Our assessment shows that the SDPs align sufficient food supply with progress towards planetary integrity, halting biodiversity loss, mitigating adverse impacts from irrigation, and significantly reducing nitrogen pollution. While all SDPs comply with the Paris climate target, they diverge in the timing of climate mitigation efforts and focus on different greenhouse gases and emission sources. The Economy-driven Innovation pathway rapidly achieves net-negative CO2 emissions from the land system, whereas the pathways Resilient Communities and Managing the Global Commons significantly decrease agricultural non-CO2 emissions. Moreover, sustainability interventions attenuate trade-offs associated with narrowly focused mitigation scenarios and reduce reliance on carbon dioxide removal strategies like bioenergy with carbon capture and storage.

The UN sustainable development goals (SDGs) and the Paris climate target require a holistic transformation towards human well-being within planetary boundaries. However, there are growing debates on how to best pursue these targets. Proposed transformation strategies include market- and technology-driven green-growth, shifting towards a sufficiency-oriented post-growth economy, and a transformation driven primarily by strong government action. Here we quantify three alternative sustainable development pathways (SDPs), Economy-driven Innovation, Resilient Communities, and Managing the Global Commons, that reflect these different societal strategies. We compare the quantifications from two integrated assessment models and two sectoral models of the buildings and materials sectors across a broad set of indicators for sustainable development and climate action. Our global multi-scenario and multi-model analysis shows that all three SDPs enable substantial progress towards the human development goals of the SDGs. They simultaneously limit global warming and prevent further environmental degradation, with the sufficiency-oriented Resilient Communities scenario showing the lowest peak warming and lowest reliance on carbon dioxide removal as well as the largest improvements in biodiversity intactness. The SDPs also alleviate the concerns about the biogeophysical and technological feasibility of narrowly-focused climate change mitigation scenarios. However, the shifts in energy and food consumption patterns assumed in the SDPs, ranging from moderate in Economy-driven Innovation to very ambitious in Resilient Communities, also lead to increased challenges regarding socio-cultural feasibility.

Climate change and inequality are critical and interrelated issues. Despite growing empirical evidence on the distributional implications of climate policies and climate risks, mainstream model-based assessments are often silent on the interplay between climate change and economic inequality. Here we fill this gap through an ensemble of eight large-scale integrated assessment models that belong to different economic paradigms and feature income heterogeneity. We quantify the distributional implications of climate impacts and of the varying compensation schemes of climate policies compatible with the goals of the Paris Agreement. By 2100, climate impacts will increase inequality by 1.4 points of the Gini index on average. Maintaining global mean temperature below 1.5 °C reduces long-term inequality increase by two-thirds but increases it slightly in the short term. However, equal per-capita redistribution can offset the short-term effect, lowering the Gini index by almost two points. We quantify model uncertainty and find robust evidence that well-designed policies can help stabilize climate and promote economic inclusion.

In this study, we analyze the effects of technology availability, political coordination, and behavioral change on transformation pathways toward net-zero greenhouse gas emissions in the European Union by 2050. We implemented an iterative stakeholder dialogue to co-design the scenarios that were calculated using a global multi-regional energy-economy-land-climate model. We find that in scenarios without behavioral change and with restriction of technologies, the target of greenhouse gas neutrality in the European Union cannot be reached. Already a target of 200 Mt CO2eq/yr requires CO2 prices above 100 €/tCO2 in 2030 across all sectors in all scenarios. The required CO2 price can increase to up to 450 €/tCO2 by 2030 if technologies are constrained, if no complementary regulatory measures are implemented, and if changes in consumer behavior towards a more sustainable lifestyle do not materialize.