Periodic Reporting for period 2 - RESCUE (Response of the Earth System to overshoot, Climate neUtrality and negative Emissions)
Période du rapport: 2024-03-01 au 2025-08-31
In December 2015 the majority of the world’s nations, under the umbrella of the United Nations, signed an international treaty on climate, which became known as the Paris Agreement (PA). The objective of the PA is to obtain commitments from signing parties to reduce greenhouse gas (GHG) emissions to levels consistent with a global warming well below 2 °C above pre-industrial levels and to pursue further efforts to limit it to 1.5 °C. The PA represents a historical landmark in the fight against climate change. However, it soon became clear that the efforts being committed by signing parties were not enough to achieve such ambitious goals. As a result, the world is currently on track to warming levels that will either temporarily or permanently overshoot both the 1.5 °C and the 2 °C goals. At present, there is a strong agreement within the climate science and policy communities that climate change mitigation through emission reduction alone, although urgent and necessary, will no longer be enough to achieve the PA’s goals.
The phase-out of fossil fuels to reduce GHG emissions can be complemented by negative emissions in the form of Carbon Dioxide Removal (CDR), with the objective to offset gross GHG emissions, and reduce atmospheric CO2 concentrations. This can be achieved with a range of methods that either aim at enhancing land and ocean carbon sinks through manipulation of natural processes or seek to engineer the direct removal of CO2 from the atmosphere followed by its storage.
To achieve global net-negative emissions, a broad set of CDR options - a CDR portfolio - will be necessary. Knowledge about CDR potentials and their feasibility is still limited considering the likely necessity of their deployment at large scale in the coming decades. Although the window of opportunity for action is rapidly closing, the commitment to large-scale implementations of CDR should not be rushed without first evaluating thoroughly their effectiveness and all the potential environmental side effects.
Overall, our understanding of how the climate and the Earth System will respond to global mean temperature stabilization, with or without an overshoot, is severely limited. This knowledge gap hampers our ability to design long-term scenarios because it is impossible to weigh the costs of a decided decarbonisation of the world’s economy against the losses caused by a period of global temperature above a given target. To this uncertainty, we must add our inability to project the effectiveness and the environmental impacts of large-scale CDR implementations that will be required to either maintain or bring back global temperature within safe limits.
The RESCUE project responds to the urgent necessity of reliable science-based recommendations to inform climate policies for the coming decades. Two overall objectives are pursued: 1) Quantify the climate and Earth system responses to pathways achieving climate neutrality by Carbon Dioxide Removal (CDR) deployment with and without temperature overshoot, and 2) Assess the potential role of CDR in reducing net GHG emissions, as well as its potential environmental risks and co-benefits.
RESCUE will expand existing knowledge on CDR methods, to design a suite of new global temperature stabilization scenarios at several target values. New model developments will deliver improved climate projections with explicit representation of CDR portfolios for these scenarios. Stakeholders will be closely engaged throughout the project to ensure policy relevance and final update of the results which will be made freely available via existing climate services.
The phase-out of fossil fuels to reduce GHG emissions can be complemented by negative emissions in the form of Carbon Dioxide Removal (CDR), with the objective to offset gross GHG emissions, and reduce atmospheric CO2 concentrations. This can be achieved with a range of methods that either aim at enhancing land and ocean carbon sinks through manipulation of natural processes or seek to engineer the direct removal of CO2 from the atmosphere followed by its storage.
To achieve global net-negative emissions, a broad set of CDR options - a CDR portfolio - will be necessary. Knowledge about CDR potentials and their feasibility is still limited considering the likely necessity of their deployment at large scale in the coming decades. Although the window of opportunity for action is rapidly closing, the commitment to large-scale implementations of CDR should not be rushed without first evaluating thoroughly their effectiveness and all the potential environmental side effects.
Overall, our understanding of how the climate and the Earth System will respond to global mean temperature stabilization, with or without an overshoot, is severely limited. This knowledge gap hampers our ability to design long-term scenarios because it is impossible to weigh the costs of a decided decarbonisation of the world’s economy against the losses caused by a period of global temperature above a given target. To this uncertainty, we must add our inability to project the effectiveness and the environmental impacts of large-scale CDR implementations that will be required to either maintain or bring back global temperature within safe limits.
The RESCUE project responds to the urgent necessity of reliable science-based recommendations to inform climate policies for the coming decades. Two overall objectives are pursued: 1) Quantify the climate and Earth system responses to pathways achieving climate neutrality by Carbon Dioxide Removal (CDR) deployment with and without temperature overshoot, and 2) Assess the potential role of CDR in reducing net GHG emissions, as well as its potential environmental risks and co-benefits.
RESCUE will expand existing knowledge on CDR methods, to design a suite of new global temperature stabilization scenarios at several target values. New model developments will deliver improved climate projections with explicit representation of CDR portfolios for these scenarios. Stakeholders will be closely engaged throughout the project to ensure policy relevance and final update of the results which will be made freely available via existing climate services.
During this second reporting period Tier-1 scenarios have been completed and the output required for ESM simulations have been harmonized and gridded, together with complementary GHG concentrations. This output has been tested by ESMs and Tier-1 climate projections are being produced by two of five ESMs. The remaining three ESMs are expected to complete the Tier-1 projections by the end of November 2025. The reduced and intermediate complexity climate models (UVic and OSCAR-MESMER) have completed the Tier-1 simulations and the results are being analyzed. Complementary land-use maps for the baseline simulations for the ESMs have been produced and are being tested. In parallel, the extension of Tier-1 scenarios have also been completed and are available to the ESMs. Tier-2 scenarios have been defined to align more strictly to the Paris agreement goals and their production has been completed, together with the relative complementary GHGs concentrations.
Meanwhile, analysis on existing simulations has progressed focusing on mean and extreme climate reversibility in overshoot scenarios and CDR efficiency. Alternative CDR techniques have been investigated focusing on the potential of enhanced rock weathering and methane removal. Moreover, work on the detectability of CDR efficiency and impacts is progressing also using existing simulations produced in CMIP6 and other ongoing projects.
Meanwhile, analysis on existing simulations has progressed focusing on mean and extreme climate reversibility in overshoot scenarios and CDR efficiency. Alternative CDR techniques have been investigated focusing on the potential of enhanced rock weathering and methane removal. Moreover, work on the detectability of CDR efficiency and impacts is progressing also using existing simulations produced in CMIP6 and other ongoing projects.
The RESCUE project advances the frontiers of Earth-system and climate-mitigation research by coupling integrated assessment models (IAMs), Earth system models (ESMs), and emulators to assess overshoot and stabilization scenarios up to the year 2300. It delivers, for the first time, a unified multi-model framework linking emission pathways, CDR deployment, and Earth-system feedbacks.RESCUE introduces fully interactive simulations of BECCS and ocean alkalinity enhancement (OAE) within ESMs, and novel scenarios consistent with Paris targets. It pioneers probabilistic emulation of IAMs and develops integrated climate-energy-carbon models directly coupling biogeochemical and socio-economic processes. Innovative studies quantify the climate and economic implications of emerging CDR options—enhanced rock weathering, atmospheric methane removal, and macroalgae farming—and their ecosystem co-benefits. RESCUE also delivers new insights into post-overshoot reversibility, revealing persistent regional asymmetries, irreversible drought and hydrological changes, and feedbacks between carbon and nutrient cycles. With 41 peer-reviewed papers, RESCUE substantially improves understanding of the biophysical and socio-economic dimensions of achieving and maintaining climate neutrality, setting new benchmarks for IAM-ESM integration and CDR assessment.