TRACKING RISKS IN FUTURE EMISSIONS, CLIMATE AND TECHNOLOGICAL ASSUMPTIONS

During the first year of the TRIFECTA project, we have seen the reality of climate change come into sharp focus. Global mean temperatures signficantly exceeded historical records, placing the world on the brink of exceeding the 1.5C target of the Paris Agreement. The consequences of this are illustrated by increasingly frequent and extreme climate impacts, in every part of the world. In TRIFECTA, we are conducting research to understand how current climate policies and net-zero ambitions translate into climate risk. Are current plans still sufficient to meet the Paris Agreement goals, despite the record temperatures of the last year and are our models fully informing us on the risks of relying on carbon capture to help reach net-zero goals? FIrstly, we have developed, documented and calibrated a new version of our flagship CICERO Simple Climate Model, with the first model desciption paper now in press. This model provides a framework for rapidly simulating millions of different future climate evolutions, while exploring underlying assumptions in how future emissions might interact with the Earth System - filling a gap which currently exists between simple and complex models by resolving land and ocean carbon cycles processes which have to date only been represented in computationally expensive models. Secondly, we have performed a series of studies to understand climate dynamics around the net-zero transition - and how simple and complex climate models differ in terms of when we might expect to see peak warming. We have coordinated an amibitious study to compare this behaviour with an international group of modeling centers - and we have designed an experiment to measure climate reversiblity which will form a core component of the climate simulations which will inform the coming IPCC assessment. Thirdly, we have coordinated a study to assess key underlying uncertainties in carbon removal in a range of models. Our perspective on the need for emissions-driven modeling highlights that economic models are making largely untested assumptions on the level of carbon capture which could potentially be delivered in the future. Our study (with a wide range of international coauthors) argues that explicitly modeling these removals in complex Earth System Models must form a central part of the next phase of climate modeling, and early indications are that this amibtion will be reflected in the next phase of simulations. Finally, we have worked extensively on scenarios - both retrospectively and forward looking. We have conducted an assessment of the use of climate scenarios in the last phase of the IPCC, and made recommendations for how they can be better and more robustly sampled in the future. We also form part of the team recommending new scenarios for international modeling efforts for the next phase of the IPCC, and we have conducted the simple climate modeling exercises to inform that effort. In the coming year, we will continue the development of the CICERO-SCM - exploiting upgraded infrastructure to implement new carbon cycle sub-models for the land and ocean. This will enable us to make robust tests of how future climate might respond to a range of emissions and carbon capture pathways. Simultaneosly, we are developing new scenarios which explore currently unsampled futures - representing geoengineering and futures in which prior assumptions about climate response or carbon capture potential are proved incorrect.

Most net-zero scenarios assume a large amount of Carbon Dioxide Removal (CDR) in the latter part of the 21st century, but the science informing the plausibility of such removals is in its infancy. TRIFECTA seeks to provide risk-framing for climate mitigation strategies on three axes: (1) by identifying mitigation trade-offs and potentially under-sampled strategies for achieving net-zero through the development of a statistical climate scenario analysis framework. (2) through the development of a cutting edge simple climate model to resolve key uncertainties in the net-zero transition, focusing on the better understanding of uncertainties associated with CDR, non-CO2 forcers and land use change. (3) providing guidance on the long-term risk associated with near-term mitigation decisions and long-term assumptions about future technological capacity and climate response parameters. TRIFECTA will develop a simple climate modeling system and risk propagation framework which will highlight the relative risks associated with net-zero strategies. We will quantify the trade-offs between different fossil fuel mitigation foci, and the factors controlling the level of deployment of CDR in current scenarios. We will then consider key physical climate processes relevant for mitigation scenarios: carbon and heat dynamics, feedbacks and the role of land use in different representative regions. Finally, we will synthesize results with a comprehensive risk assessment for a set of representative global net zero strategies, highlighting their exposure to physical, technological and economic uncertainties as represented in global mean temperature trajectories.