Disentangling the roles of late Miocene palaeogeography and vegetation – Implications for climate sensitivity

Bradshaw, Catherine; Lunt, Daniel J.; Flecker, Rachel; Davies‐Barnard, Taraka

doi:10.1016/j.palaeo.2014.10.003

Cited by 26 publications

(39 citation statements)

References 92 publications

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“…As such, HadCM3BL has been used exten-sively for our pre-Quaternary climate modelling work (e.g. Marzocchi et al, 2015b;Bradshaw et al, 2015;Kennedy et al, 2015;Loptson et al, 2014).…”

Section: Hadcm3blmentioning

confidence: 99%

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

et al. 2017

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Abstract. Understanding natural and anthropogenic climate change processes involves using computational models that represent the main components of the Earth system: the atmosphere, ocean, sea ice, and land surface. These models have become increasingly computationally expensive as resolution is increased and more complex process representations are included. However, to gain robust insight into how climate may respond to a given forcing, and to meaningfully quantify the associated uncertainty, it is often required to use either or both ensemble approaches and very long integrations. For this reason, more computationally efficient models can be very valuable tools. Here we provide a comprehensive overview of the suite of climate models based around the HadCM3 coupled general circulation model. This model was developed at the UK Met Office and has been heavily used during the last 15 years for a range of future (and past) climate change studies, but has now been largely superseded for many scientific studies by more recently developed models. However, it continues to be extensively used by various institutions, including the BRIDGE (Bristol Research Initiative for the Dynamic Global Environment) research group at the University of Bristol, who have made modest adaptations to the base HadCM3 model over time. These adaptations mean that the original documentation is not entirely representative, and several other relatively undocumented configurations are in use. We therefore describe the key features of a number of configurations of the HadCM3 climate model family, which together make up HadCM3@Bristol version 1.0. In order to differentiate variants that have undergone development at BRIDGE, we have introduced the letter B into the model nomenclature. We include descriptions of the atmosphere-only model (HadAM3B), the coupled model with a low-resolution ocean (HadCM3BL), the high-resolution atmosphere-only model (HadAM3BH), and the regional model (HadRM3B). These also include three versions of the land surface scheme. By comparing withPublished by Copernicus Publications on behalf of the European Geosciences Union. observational datasets, we show that these models produce a good representation of many aspects of the climate system, including the land and sea surface temperatures, precipitation, ocean circulation, and vegetation. This evaluation, combined with the relatively fast computational speed (up to 1000 times faster than some CMIP6 models), motivates continued development and scientific use of the HadCM3B family of coupled climate models, predominantly for quantifying uncertainty and for long multi-millennial-scale simulations.

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“…As such, HadCM3BL has been used exten-sively for our pre-Quaternary climate modelling work (e.g. Marzocchi et al, 2015b;Bradshaw et al, 2015;Kennedy et al, 2015;Loptson et al, 2014).…”

Section: Hadcm3blmentioning

confidence: 99%

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

et al. 2017

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“…Climate feedbacks driven by these changes in terrestrial vegetation have been hypothesised to be partially responsible for some of the major past climate states (e.g. Bradshaw et al, 2015;Claussen et al, 2006;Crucifix and Loutre, T. Davies-Barnard et al: Terrestrial biosphere carbon emissions 2002;de Noblet et al, 1996;Zhou et al, 2012), with many studies particularly focussing on the biogeophysical effects at the Last Glacial Maximum (LGM) (e.g. Hopcroft and Valdes, 2014;Jahn et al, 2005;Kageyama et al, 2012;O'ishi and Abe-Ouchi, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…However, model simulations have generally focussed on either the biogeophysical impacts of vegetation changes (e.g. Bradshaw et al, 2015;Claussen et al, 2006;Jahn et al, 2005;O'ishi and Abe-Ouchi, 2013;Shellito and Sloan, 2006) or biogeochemical impacts (e.g. Kaplan et al, 2002;Ciais et al, 2012) and the question of the overall feedback on climate rarely addressed, although Claussen (2009) argues that the net effect at the LGM is dominated by the biogeophysical effects.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics

et al. 2017

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Abstract. The terrestrial biosphere is thought to be a key component in the climatic variability seen in the palaeorecord. It has a direct impact on surface temperature through changes in surface albedo and evapotranspiration (so-called biogeophysical effects) and, in addition, has an important indirect effect through changes in vegetation and soil carbon storage (biogeochemical effects) and hence modulates the concentrations of greenhouse gases in the atmosphere. The biogeochemical and biogeophysical effects generally have opposite signs, meaning that the terrestrial biosphere could potentially have played only a very minor role in the dynamics of the glacial-interglacial cycles of the late Quaternary. Here we use a fully coupled dynamic atmosphereocean-vegetation general circulation model (GCM) to generate a set of 62 equilibrium simulations spanning the last 120 kyr. The analysis of these simulations elucidates the relative importance of the biogeophysical versus biogeochemical terrestrial biosphere interactions with climate. We find that the biogeophysical effects of vegetation account for up to an additional −0.91 • C global mean cooling, with regional cooling as large as −5 • C, but with considerable variability across the glacial-interglacial cycle. By comparison, while opposite in sign, our model estimates of the biogeochemical impacts are substantially smaller in magnitude. Offline simulations show a maximum of +0.33 • C warming due to an increase of 25 ppm above our (pre-industrial) baseline atmospheric CO 2 mixing ratio. In contrast to shorter (century) timescale projections of future terrestrial biosphere response where direct and indirect responses may at times cancel out, we find that the biogeophysical effects consistently and strongly dominate the biogeochemical effect over the inter-glacial cycle. On average across the period, the terrestrial biosphere has a −0.26 • C effect on temperature, with −0.58 • C at the Last Glacial Maximum. Depending on assumptions made about the destination of terrestrial carbon under ice sheets and where sea level has changed, the average terrestrial biosphere contribution over the last 120 kyr could be as much as −50 • C and −0.83 • C at the Last Glacial Maximum.

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“…Modelling efforts of the Miocene find that reconciling the combined constraints of ocean temperature, CO2 indicators and Antarctic ice sheet dynamics is a non-trivial task (Micheels et al, 2009;Henrot et al, 2010, Bradshaw et al, 2012Sijp et al, 2014), with vegetation seemingly integral in creating the Miocene climatic conditions (Henrot et al, 2010;Knorr et al, 2011;50 Krapp and Jungklaus, 2011;Micheels et al, 2011;Bradshaw et al, 2015) along with bathymetry, topography and CO2.…”

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confidence: 99%

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Crichton¹,

Ridgwell²,

Lunt³

et al. 2020

Preprint

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Abstract. Since the middle Miocene, 15 Ma (million years ago), the Earth’s climate has undergone a long-term cooling trend, characterised by a reduction in sea surface temperatures by over 6 °C, with 4 to 6 °C cooling occurring in the deep ocean. The causes of this cooling are primarily thought to be linked to changes in ocean circulation due to tectonic plate movements affecting ocean seaways, together with and a drop in atmospheric greenhouse gas forcing (and attendant ice-sheet growth and feedback). In this study we assess the potential to constrain, using marine sediment proxy data, the evolving patterns of global ocean circulation and cooling of surface climate over the last 15 million years (Ma) in an Earth system model. We do this by compiling surface and benthic ocean temperature and benthic carbon-13 data in a series of seven time-slices spaced at approximately 2.5 million year intervals. We pair this with a corresponding series of seven tectonic and surface climate boundary condition reconstructions in the cGENIE (muffin release) Earth system model. In the cGENIE model, we adjust atmospheric CO2 together with the magnitude of North Pacific to North Atlantic salinity flux adjustment in a series of 2D parameter ensembles in order to match global temperature and benthic δ13C patterns in the model to the data. We identify that a relatively high CO2 equivalent forcing of 1120 ppm is required at 15 Ma in cGENIE to reproduce proxy temperature estimates in the model, noting that this CO2 forcing is dependent on cGENIEs climate sensitivity (which is as the present day) and that it incorporates the effects of all greenhouse gases. The required CO2 forcing progressively reduces throughout the subsequent six time slices delineating the observed long-term cooling trend. In order to match the evolving patterns of the proxy data, we require fundamental change in the mode of ocean circulation at 12.5 Ma with present-day-like benthic δ13C trends established by 10 Ma. We also find a general increasing strength of Atlantic overturning despite a reduction in salinity of the surface North Atlantic over the cooling period, attributable to falling intensity of the hydrological cycle and polar cooling caused by CO2-driven global cooling.

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Disentangling the roles of late Miocene palaeogeography and vegetation – Implications for climate sensitivity

Cited by 26 publications

References 92 publications

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

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