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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CRESCENDO (Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination and Outreach)

Teaser

Summary

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 commonly referred to as Earth system models (ESMs) and are the primary tools available 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 capabilities and 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, in particular, its sensitivity to changing external forcing, such as future increases in anthropogenic emission of CO2. The ESMs will provide a coordinated set of state-of-the-art 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 also 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.

Work performed

A significant effort has gone into preparing for the CMIP6 exercise, including: (i) Finalizing all model components and couplings intended for use in the respective CMIP6 models; (ii) Ensuring the coupled ESMs are well balanced in terms of global energy and carbon constraints; (iii) Implementing CMIP6 forcing data into the models; (iv) Bringing the model ocean and land states into equilibrium with the CMIP6 pre-industrial forcing; (v) Introducing the diagnostic output requested from the CMIP6 model inter-comparison projects (MIPs) into the project ESMs; (vi) Working to ensure the Earth System Grid Federation (ESGF) is capable of storing and broadcasting the petabytes of data that will be produced in CMIP6. Most of this work is now complete and six of the seven ESMs have started CMIP6 simulations. Four groups have completed the CMIP6 DECK and historical simulations, performing large ensembles of historical simulations (1850-2015). Two ESMs are in the process of running the DECK and will start historical runs early in 2019 and the 7th group, after some difficulties, should begin their simulations in January 2019.
In addition to the CMIP6 DECK and historical runs, 4 groups have also begun future projections, following the scenarioMIP Tier 1 emission scenarios. The other 3 groups will begin these future projections early in 2019. Simulations are also now occurring for the other MIPs targeted by the project (C4MIP, AerChemMIP, LUMIP, LS3MIP and OMIP).
CRESCENDO scientists have been actively engaged in the international effort to design CMIP6 exercise, as well as developing the science and experiment protocols for the six MIPs at the core of CRESCENDO. These have led to peer-reviewed papers documenting their overall design and experiment protocols.
The 3 Integrated Assessment Model (IAM) groups have completed all the Historical (1850-2015) and Tier 1 and Tier 2 scenarioMIP (2015-2100) emission and land use data sets required by CMIP6. This data has been delivered in a standard format to the CMIP6 input4MIPs website.
Work has continued using the new science of emergent constraints to reduce uncertainty in future climate change feedbacks and in the overall future warming response to increasing CO2. We have also continued developing methods for weighting future climate change projections, aiming to give weight in a multi-model projection ensemble to models that are unrelated to each other in their development history and perform well for the climate change features of interest, when evaluated for the same feature against observations over the recent past.
The CRESCENDO dissemination team has been very active presenting at COP and in Brussels at the EP, and produced two policy documents on potential pathways for realizing the 2015 Paris Agreement. The CRESCENDOschools Network has been established and ran an open call for school students to developing an innovative approach to communicating about climate change and potential solutions. This call was won by a school in Albania who presented their work at the 2018 Climateurope Festival in Belgrade.

Final results

The CRESCENDO models running in CMIP6 go beyond the state of the art compared to earlier models (e.g. in CMIP5), through inclusion of more advanced and, in some cases, completely new representations of important biogeochemical and aerosol processes: the majority of models now include a representation of nitrogen limitation on terrestrial carbon uptake; use a common approach to implementing human land use in the ESMs; a more realistic representation of cloud-aerosol processes, including new couplings between the terrestrial and marine biospheres and atmospheric aerosol and trace gases; and fully interactive stratosphere-troposphere chemistry models, coupled to aerosol-cloud-radiation parameterizations. In the ocean, models also include more complete treatment of ocean biological processes, in some cases including riverine nutrient input to the ocean. The high-resolution versions of the CRESCENDO models employ ocean models with unprecedented spatial resolution (e.g. 0.25Â°) in the context of coupled Earth system models with interactive ocean biogeochemistry. The impact of such increased model resolution on simulated marine carbon uptake will be an important project outcome.
The use of ESMValTool for a coordinated evaluation of the CMIP6 multi-model ensemble is a significant advance on CMIP5. ESMValTool now runs directly on CMIP6-compliant data stored on the ESGF and can therefore make rapid multi-model inter-comparisons as data becomes available. This facility will be used by the IPCC AR6 Working Group I Technical Support Unit (TSU).
The set of future projections produced by CRESCENDO are based on a more complete representation of the Earth system than earlier data sets and will, therefore, provide more believable projections of the Earth system response to future CO2 emissions. Furthermore, the new CMIP6 emission scenarios, developed by CRESCENDO scientists, are each based on a specific socio-economic development pathway (so-called Shared Socio-economic Pathways), increasing the utility of the resulting projections for analysis across physical climate change, climate change impacts and mitigation science. These projections will underpin much of the IPCC AR6 process.