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Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination and Outreach

Periodic Reporting for period 3 - CRESCENDO (Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination and Outreach)

Reporting period: 2018-11-01 to 2021-03-31

Global Climate Models (GCMs) continue to be extended in their process realism, through the inclusion of new and/or more advanced representation of key biogeochemical processes. Such models are referred to as Earth system models (ESMs) and are the primary tools for making future projections of global climate change, linking such projected changes to allowable carbon emissions commensurate with staying below a given warming target. ESMs allow an assessment of the potential response of the full global environment (including biological and chemical components) to future climate change. Such assessments are important for developing sustainable future development pathways.

CRESCENDO aims to increase the scientific realism of 7 European ESMs through targeted improvements to a range of key processes. These will be evaluated against observations and the improved ESMs applied in the World Climate Research Program (WCRP) 6th Coupled Model Intercomparison Project (CMIP6). Analysis of the ESMs will deliver an improved understanding of how the coupled Earth system operates and its sensitivity to future increases in anthropogenic emission of CO2. The ESMs will provide a coordinated set of Earth system projections for the coming century and beyond.

IPCC AR5 highlighted that a new set of policy-relevant questions can be addressed by ESMs, such as; the level of CO2 emissions compatible with a given climate stabilization target. ESMs are increasingly of interest to investigate climate mitigation policies (such as Bio-Energy with Carbon Capture and Storage, BECCS) and the co-benefits of addressing climate change and air quality challenges in combined manner. To increase our overall confidence in future projections made by ESMs, CRESCENDO targets a systematic improvement in our ability to evaluate these models against observations.
During the second half of CRESCENDO, key project objectives were realized, including:
(i) The CMIP6 configurations of the project ESMs were documented in peer reviewed literature; (ii) The ESMs simulated the CMIP6 DECK and historical period, and the six MIPs targeted by CRESCENDO. A number of the project ESMs were used for a new MIP (ZECMIP, Zero Emission Commitment MIP), developed from a workshop sponsored by CRESCENDO; (iii) Data from all MIPs, the DECK and historical simulations were delivered to the Earth System Grid Federation (ESGF); (iv) The (emission and land use) forcing data sets used in CMIP6 were documented; (v) A new version (2.0) of ESMValtool was developed and released, with a suite of new diagnostics; (vi) A new bias correction scheme was developed for ISIMIP3.

Analysis of the various CMIP6 simulations resulted in a large number of publications covering topics such as; climate sensitivity, emergent constraints, weighting of model projections, historical radiative forcing, carbon cycle feedbacks, chemistry-climate feedbacks and natural aerosol feedbacks.

Finally, a range of dissemination activities have occurred; to policymakers, high school students and the public using web and social media applications developed in the project. We highlight a few of these activities in the main progress report, linking them to specific project objectives. At the time of writing, the number of CRESCENDO publications stands at slightly more than 300. We expect this figure will increase over the coming 6 months, likely exceeding 350 publications.
A key outcome from CRESCENDO is the increased process realism of the seven participating Earth system models. Key improvements to the models include; (i) inclusion of the effects of nitrogen limitation on terrestrial carbon uptake. (ii) internally consistent treatment of human land use. (iii) an improved treatment of the marine biological carbon pump. (iv) an increased degree of prognostic coupling between emissions of marine and terrestrial natural aerosol and their processing in the atmosphere. (v) a fully interactive treatment of atmospheric chemistry and aerosols. This increased degree of process realism and coupling means the models are able to simulate a larger range of future feedbacks that may occur in the real world. Improved Earth system models result in more reliable future projections across a range of variables, encompassing the physical, chemical and biological facets of the Earth system. Access to more reliable future projections is an important outcome for European policymakers that can help in planning climate change mitigation actions and in developing sound adaptation strategies. This can result in significant, long-term benefits for the European public, including European businesses and the overall socio-economic system.

CRESCENDO coordinated the European contribution to the scenarioMIP activity within CMIP6. This is the main project delivering new future projections into the IPCC 6th Assessment Report (AR6). The report will be the main climate science guide for policymakers over the coming 5 years. The contribution from CRESCENDO represents an important component of this global effort, which has moved the science beyond what was state-of-the-art.

In the field of emergent constraints and weighting of projections, CRESCENDO has moved the science beyond what was state-of-the art. Emergent constraints can help focus model development onto those processes that are key in controlling the future feedback response of ESMs to increasing CO2 emissions. Doing this can lead to models more reliably simulating future feedbacks, resulting in more reliable future projections. Similarly, an improved use of model weighting can mean that for specific topics, for example agricultural change over Europe, an impact modeller will be able to use the weighting approach to maximize selection of the best performing models for the region and variables of interest to their application. This should lead to more reliable downstream activities where ESM projection data is used, for example in climate impacts modelling. In both cases the net result are more reliable future projection data for subsequent downstream activities, with potential socio-economic benefits.

CRESCENDO has helped to advance Earth system model evaluation, through development and release of ESMValTool vn2.0. This tool is used around the world for model evaluation. Version 2.0 is more efficient than earlier versions and includes an array of new diagnostics developed in CRESCENDO and is available to any researcher. These include diagnostics for; terrestrial carbon and nitrogen cycle, marine biological pump, emissions of natural marine and terrestrial aerosols. All these developments indirectly contribute to improved Earth system models around the world, with potential socio-economic benefits.

Our CRESCENDOschools network was a success. We worked with 16 to 18 year old students, helping them to understand more about the science of Earth system modelling. We took part in public science outreach events where we discussed the type of research we do with the public. The ScienceBrief platform provides the public and media with a quick and reliable explanation of key climate science papers. While there are no direct socio-economic benefits from these activities there can potentially be large, non-measurable impacts on public behaviour and political engagement. These indirect impacts should not be underestimated.