EC-Earth

Earth System Models such as EC-Earth are currently the only way of providing society with information on the future climate. EC-Earth generates projections of global climate change, which are a prerequisite to support the development of national adaptation and mitigation strategies.

EC-Earth is a global climate model system based on the idea to use the world-leading weather forecast model of the ECMWF (European Centre of Medium Range Weather Forecast) in its seasonal prediction configuration as the base of climate model. The model system can be used in several configurations including the classical climate model (atmosphere, soil, ocean, sea ice) and Earth System configurations (adding atmospheric chemistry and aerosols, ocean bio-geo-chemistry, dynamic vegetation and a Greenland ice sheet). The model is developed by the European EC-Earth consortium with SMHI as core partner leading the development and other Swedish partners from the universities of Lund, Stockholm, Gothenburg and Uppsala.  The model in its different configurations and resolutions is used for climate change projections, predictions and process studies. EC-Earth 3, the current version, is prepared for the 6th phase of the Climate Model Intercomparison Project (CMIP6).

Model description

The EC-Earth Earth System Model (ESM) describes the global climate system and its evolution in time by a combination of coupled physical and biogeochemical processes.  The current version EC-Earth 3 is based on

  • ECMWF's atmospheric circulation model IFS, cycle 36r4, including the land surface model H-Tessel

  • the current version of the ocean model NEMO3.6, including the Louvain-la-Neuve Sea Ice Model (LIM3)

  • the PISCES v2 ocean bio-geo-chemistry component.

  • The dynamical vegetation model LPJ-GUESS v4

  • the atmosphere composition and aerosol model TM5

  • the PISM 0.7 ice sheet model

The model components are coupled via the Oasis-3 MCT coupler. A more detailed summary of model component can be found here.

Model development

The development of the EC-Earth model is a shared task of the EC-Earth community, currently lead by SMHI.  The community is organized in work groups (WGs) lead by the Steering Group (SG). Both WGs and SG maintain a communication with corresponding entities at ECMWF and the NEMO team to ensure benefits for both sides.

Since EC-Earth v2.3, the CMIP5 version, all model components have been upgraded and the way of collaboration within the growing consortium has been greatly facilitated. In an effort to make the complex model more suitable for new users and a growing community, a number of technical aspects have been reconsidered. EC-Earth 3 comes with a greatly simplified configuration procedure and build system, including a graphical user interface, which allows an easy to use and interactive way of configuration. Moreover, portability of EC-Earth 3 has been addressed and is substantially improved.

Acknowledging the fact that scientific software development is a complex matter, the development process itself has been adapted to follow established best practices for software projects as far as possible. As a result, all development activities are now directed to the EC-Earth 3 Development Portal, a web based service that covers version control, issue tracking, documentation, and other means of communication between users and developers.

Focus areas of model development are a number of flexible model configurations such as different combinations of ESM model components and resolutions, good climate performance of standalone and coupled configurations and the full implementation of CMIP6 standard forcing and output standards. As an example for the recent state of development, Fig. 1 shows the simulated 2-m atmospheric temperature for the Northern hemisphere summer.

Model tuning as part of the model development applies a number of constraints such as energy and mass budgets close to observations, at the top of the atmosphere and at the surface, in particular between  atmosphere and ocean. Model biases such as for temperature, precipitation and circulation are minimized.

Model evaluation

Different model configurations are tuned towards observed climate conditions. The resulting model is then subject to a spin-up under pre-industrial conditions, followed by a historical simulation between 1850 and today. Those simulations are to be carried out during autumn 2017. The resulting climate performance will then be analysed by standard diagnostics focusing on global and regional biases, seasonal cycles, climate sensitivity, climate modes of variability, and predictive capability.

Application of EC-Earth

After the model evaluation, model experiments in line with CMIP6 tasks will be carried out (more on Global climate scenarios). SMHI is most interested in new climate scenarios following the new emission scenario framework (O'Neill et al. 2016) of Shared Socio-economic Pathways (SSP). Previous climate scenario simulations have been carried out with an older version of EC-Earth (Koenigk et al., 2013, Fig.2) and different forcing datasets. 

Figure 2 EC-Earth
Fig 2. Projected annual mean 2-meter air temperature change in °C in EC-Earth, between 2080–2099 and 1980–1999 in RCP2.6 (low greenhous gas emissions), RCP4.5 (medium emissions)and RCP8.5 (high emissions) (Koenigk et al. 2013)

Recently,

  • links between Arctic surface variability and its interaction with lower latitudes have been examined (Caian et al. 2016, Koenigk and Brodeau 2016, Brodeau and Koenigk 2016),

  • the sensitivity to Arctic sea ice changes on European climate variability at different global surface warming levels (Wang et al. 2017)

  • the sensitivity of the west African and South Asian monsoon to model resolution has been explored (Wang et al. 2016)

  • changes in climate variability and extremes  at the 3 warming levels have been examined (Wyser et al. 2017, Wang et al. 2017),

  • Effects of increased resolution in Earth system models in general and more specifically on Southern Ocean variability has been tested (Wang et al. 2016, Wyser et al. 2017, Wyser et al. 2016, Wyser et al. 2014)

Different configurations of the EC-Earth models are used in Swedish, Nordic, European and other international projects such as CRESCENDO, PRIMAVERA and IMPREX for climate scenarios, climate prediction experiments and climate process studies. Results are key input to climate change information for national and international stakeholders and for climate services. Furthermore, the global model simulations with EC-Earth deliver boundary conditions for further downscaling by regional climate models.

References

Caian, M., Koenigk, T., Döscher, R., & Devasthale, A. (2017). An interannual link between Arctic sea-ice cover and the North Atlantic Oscillation. Climate Dynamics, 1-19. doi:10.1007/s00382-017-3618-9

Brodeau, L., & Koenigk, T. (2016). Extinction of the northern oceanic deep convection in an ensemble of climate model simulations of the 20th and 21st centuries. Climate Dynamics, 46(9-10), 2863-2882. doi:10.1007/s00382-015-2736-5

Koenigk, T., & Brodeau, L. (2016). Arctic climate and its interaction with lower latitudes under different levels of anthropogenic warming in a global coupled climate model. Climate Dynamics, 1-22. Clim Dyn (2016). doi:10.1007/s00382-016-3354-6

Koenigk, T., Brodeau, L., Graversen, R. G., Karlsson, J., Svensson, G., Tjernström, M., ... & Wyser, K. (2013). Arctic climate change in 21st century CMIP5 simulations with EC-Earth. Climate Dynamics, 40(11-12), 2719-2743. doi:10.1007/s00382-012-1505-y

O’Neill, B. C., C. Tebaldi, D. van Vuuren, V. Eyring, P. Friedlingstein, G. Hurtt, R. Knutti et al. "The Scenario Model Intercomparison Project (ScenarioMIP) for CMIP6, Geosci. Model Dev. Discuss., doi: 10.5194." (2016).

Wang S., C. Jones and R. Döscher (2016): Report on the sensitivity of the west African and South Asian monsoon to model resolution. Report 1.6 to the EU FP7 EMBRACE programme.

Wang, S., K. Wyser and G. Strandberg, 2017: The impact of Arctic SST/SIC changes and North Atlantic Ocean SST changes associated with high end SWLs on European climate variability. Report 3.3 to the EU FP7 HELIX programme.”

Wyser K., G. Strandberg, J. Caesar, L. Gohar (2017): Documentation of changes in climate variability and extremes simulated by the HELIX AGCMs at the 3 SWLs and comparison to changes in equivalent SST/SIC low-resolution CMIP5 projections. Report 3.1 to the EU FP7 HELIX programme.

Wyser K., M. Evaldsson and C. Jones (2016): Contribution of high resolution with improved ESMs in terms of documented metrics. Report 4.5 to the EU FP7 EMBRACE programme.

Wyser K., C. Jones and T. Königk (2014): Assessment of the benefits of increased atmospheric resolution on simulated Southern Ocean variability and ocean momentum drag. Report 2.5 to the EU FP7 EMBRACE programme