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Science Week 2016: Modelling the future global climate
17 November 2016

This year and last were significant for global climate change. Carbon dioxide levels last year reached 400 ppm, while 2016 will see the global average stay above 400 ppm. This year saw the hottest July on record and is projected to be the hottest year on record.

In a changing climate, the need for more accurate reliable projections of the future global climate system is evident.  The Coupled Model Intercomparison Project (CMIP) organised under the World Climate Research Program was set up to compare global coupled climate models, in order to better understand past and future climate change. Since it started 20 years ago, it has become a key element of climate science, and has formed an important part of the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.

EC-Earth is a consortium of European countries set up to develop a new improved fully coupled Atmosphere-Ocean-Land-Biosphere global climate model. Met Éireann and ICHEC form the EC-Earth consortium for Ireland. Met Éireann has contributed to CMIP5 with EC-Earth, and will contribute to the latest CMIP6 phase.

The EC-Earth model is an atmospheric/oceanographic general climate model. Its atmospheric component is the IFS model developed at ECMWF, the ocean component is the NEMO global ocean circulation model, and it also has a sea ice model developed at the University of Louvaine-la-Neuve. ECEarth is being developed continuously, with new physics and processes incorporated into new versions. The latest version (3.2) will contribute towards CMIP6. It includes a vegetation and ocean biogeochemistry model, and an updated coupler.

Met Éireann ran CMIP5 simulations to 2100 under medium to high radiative RCP forcings. The animation below shows the change in annual 2m temperature with respect to the 1961-1990 baseline, for different RCP scenarios. For CMIP6 Met Éireann will be involved in running simulations under low to high RCPs up to 2100 at about 80km resolution with the updated version of EC-Earth. It will also carry out simulations at high resolution (40 km). Running at increased resolution allows better simulation of small scale phenomena with impacts such as tropical cyclones, and tropical-extratropical interactions. It is intended these simulations will lead to more accurate projections of the future global climate and to a better understanding of the climate system and of the impact climate change has on societies.

The annual 2 m temperature change with respect to the 30-year baseline (1961-1990) for the RCP4.5 (medium) and RCP8.5 (high) CMIP5 scenarios. (Met Éireann and ICHEC).

In a changing global climate, the need for more accurate coupled models is ever more useful when simulating future climate. As well as scenario experiments (MIPs) dealing with atmospheric and oceanographic processes, CMIP6 will also include experiments examining other parts of the climate system. Understanding the future behaviour of the Greenland ice sheet, for example, is important considering its sea level equivalent is 7 metres and it has been losing mass at an increasing rate over the last few decades. New CMIP6 experiments (ISMIP) will aim to improve estimates of the contribution of sea level rise from the melting ice sheets using atmospheric-oceanographic general climate models coupled with ice sheet models. The EC-Earth model has been coupled with the PISM ice sheet model for Greenland, and will take part in the ISMIP experiments.

For further information contact Jonathan McGovern (Jonathan dot McGovern AT met dot ie).


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