Development and evaluation of an Earth-system model – HadGEM2

Abstract

Abstract. We describe here the development and evaluation of an Earth system model suitable for centennial-scale climate prediction. The principal new components added to the physical climate model are the terrestrial and ocean ecosystems and gas-phase tropospheric chemistry, along with their coupled interactions. The individual Earth system components are described briefly and the relevant interactions between the components are explained. Because the multiple interactions could lead to unstable feedbacks, we go through a careful process of model spin up to ensure that all components are stable and the interactions balanced. This spun-up configuration is evaluated against observed data for the Earth system components and is generally found to perform very satisfactorily. The reason for the evaluation phase is that the model is to be used for the core climate simulations carried out by the Met Office Hadley Centre for the Coupled Model Intercomparison Project (CMIP5), so it is essential that addition of the extra complexity does not detract substantially from its climate performance. Localised changes in some specific meteorological variables can be identified, but the impacts on the overall simulation of present day climate are slight. This model is proving valuable both for climate predictions, and for investigating the strengths of biogeochemical feedbacks.

Reduced cooling following future volcanic eruptions

“…This a coupled atmosphere-ocean general circulation model (GCM), which includes terrestrial and ocean carbon cycle components, interactive tropospheric aerosols and an interactive tropospheric chemistry scheme (HadGEM2 Development Team 2011;Collins et al 2011). The atmospheric resolution of the model is 1.875 × 1.25° (longitude-latitude), with 38 vertical levels reaching to just over 39 km, with 11 levels above 15 km and resolving the lower stratosphere.…”

“…We performed an ensemble of simulations with the HadGEM2-ES Earth System model (HadGEM2 Development Team 2011; Collins et al 2011) of a Tambora 1815 -like eruption in pre-industrial (Kandlbauer et al 2013) and Representative Concentration Pathway 6.0 (RCP 6.0) conditions for the years AD1860 and AD2045, respectively. Tambora was chosen because it provides a very strong forcing which can be more easily separated from simulated internal variability.…”

Climate-driven disturbances in the San Juan River sub-basin of the Colorado River

“…In the Coupled Model Intercomparison Project phase 5 (CMIP5), several ESMs contain dynamic vegetation models (Collins et al, 2011;Watanabe et al, 2011;Brovkin et al, 2013b). ESMs in CMIP5 model fractional plant functional types (PFTs) and include feedbacks to the climate and land surface driven by atmospheric simulations.…”

“…2a and b; Abatzoglou and Brown, 2012) and again disaggregated to hourly intervals via the algorithms described in Bohn et al (2013). We selected the four ESMs from CMIP5 because they implemented dynamic vegetation processes: HadGEM2-ES (Collins et al, 2011;Cox, 2001), MIROC-ESM (SIEB-DGVM; Watanabe et al, 2011;Sato et al, 2007), MPI-ESM-LR (JSBACH; Giorgetta et al, 2013;Reick et al, 2013), and IPSL-CM5B-LR (ORCHIDEE; Krinner et al, 2005). We used the representative concentration pathway (RCP) 8.5 emissions scenario, which stipulates strongly increasing emissions by 2100 (Van Vuuren et al, 2011) and corroborates current emissions on par with RCP 8.5 (Le Quéré et al, 2015).…”

Assessing the contribution of different factors in regional climate model projections using the factor separation method

“…the coarse resolution setting of Med-CORDEX. The initial and lateral meteorological boundary conditions for the scenario runs were provided by two GCMs involved in the CMIP5 experiment (Taylor et al, 2012): HadGEM (Collins et al, 2011) and MPI (Jungclaus et al, 2010). The selection of these GCMs was based on a preliminary analysis showing that they performed relatively well over the European region (see also Brands et al, 2013).…”