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.

nous of main sequence stars, having masses 0.1-0.5 times the mass of the Sun. The habitable zones around such stars Planets within the habitable zones of M dwarfs are likely to are therefore very close, being typically between 0.03 and be synchronous rotators; in other words, one side is permanently illuminated while the other side is in perpetual darkness. We 0.4 AU [see Fig. 16 of Kasting et al. (1993)]. A planet lying present results of three-dimensional simulations of the atmo-this close to its star will tend to become tidally locked, or spheres of such planets, and comment on their possible habit-in other words be permanently illuminated on one side, ability. Near the ground, a thermally direct longitudinal cell as the threshold for tidal locking after 4.5 byr is r lock Ȃ exists, transporting heat from the dayside to the nightside. The 0.5(M star /M sun ) 1/3 [see Fig. 16 of Kasting et al. (1993) and circulation is three-dimensional, with low-level winds returning Dole (1964)]. Such planets are termed synchronous rotamass to the dayside across the polar regions. Aloft, the zonally tors, and their rotation rates are therefore governed by averaged winds display a pattern of strong superrotation due to the size of their orbits (this is dealt with below). these planets' finite (albeit small) rotation rate. With terrestrialIf the atmosphere of such a planet is in radiativevalues of insolation, a CO 2 /H 2 O atmosphere collapses, or con-convective equilibrium, the surface temperature T 0 on the denses on the surface of the darkside, when surface pressure dayside will be very high, while the nightside will be so is approximately 30 mb, this value being much lower for a N 2 cold that the major atmospheric constituent will condense atmosphere. This temperature contrast is also sensitive to facout on the surface. When this happens, the surface tempertors such as gravity, planetary radius, and IR optical depth .ature of the darkside, as well as the mean surface pressureThese results question the suitability of the concept of a habitp 0 , is set by a balance between upwelling thermal radiation able zone around M dwarfs that is independent of planetary and release of latent heat by condensing constituents, simiparameters. If CO 2 partial pressure is controlled by the carbonlar to the scenario that has been postulated for the martian ate-silicate cycle, we find that these planets should have a atmosphere at those times when a permanent polar cap minimum surface pressure of 1000-1500 mb of CO 2 , as this is forms (see, e.g., Toon et al. 1980). In this latter case, surface the minimum pressure needed to support stable liquid water pressures have been modeled as being as low as 1-3 mb on the darkside at the inner edge of the habitable zone. We finally conclude that planets orbiting M stars can support atmo- (Toon et al. 1980). This phenomenon is termed atmospheric spheres over a large range of conditions and, despite constraints collapse, and has been put forward as the primary reason such as stellar activity, are very likel...

The land/sea warming contrast is a phenomenon of both equilibrium and transient simulations of climate change: large areas of the land surface at most latitudes undergo temperature changes whose amplitude is more than those of the surrounding oceans. Using idealised GCM experiments with perturbed SSTs, we show that the land/sea contrast in equilibrium simulations is associated with local feedbacks and the hydrological cycle over land, rather than with externally imposed radiative forcing. This mechanism also explains a large component of the land/sea contrast in transient simulations as well. We propose a conceptual model with three elements: (1) there is a spatially variable level in the lower troposphere at which temperature change is the same over land and sea; (2) the dependence of lapse rate on moisture and temperature causes different changes in lapse rate upon warming over land and sea, and hence a surface land/sea temperature contrast; (3) moisture convergence over land predominantly takes place at levels significantly colder than the surface; wherever moisture supply over land is limited, the increase of evaporation over land upon warming is limited, reducing the relative humidity in the boundary layer over land, and hence also enhancing the land/sea contrast. The non-linearity of the Clausius–Clapeyron relationship of saturation specific humidity to temperature is critical in (2) and (3). We examine the sensitivity of the land/sea contrast to model representations of different physical processes using a large ensemble of climate model integrations with perturbed parameters, and find that it is most sensitive to representation of large-scale cloud and stomatal closure. We discuss our results in the context of high-resolution and Earth-system modelling of climate change