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A proposal for collaboration between the Hadley Centre, NERC and the Earth Simulator Centre
This outline proposal was developed following discussions during the visit of Dr. Keiko Takahashi of the Earth Simulator Centre to the Hadley Centre and NCAS/CGAM during May 2003.
Background:
A clear imperative is to develop models of much higher resolution, so as to be able to simulate explicitly flows down to smaller scales and to capture potential non-linear interactions between different space and time scales, and between different components of the Earth system. The current, state-of-the-art coupled climate models have a typical resolution of ~30 (N48) in the atmosphere and ~10 in the ocean. In neither component are key aspects of the climate system (such as the influence of ocean eddies, orographic forcing of the atmosphere, El Nino, tropical cyclones) adequately represented. There is a strong case for high resolution in all components of the coupled system. For the ocean, there is good evidence that an eddy permitting ocean model provides much better definition of western boundary currents, and also gives a more accurate simulation of equatorial waves, which are a key part of El Nino. High-resolution simulations of the atmosphere have already demonstrated significant improvements in the representation of storm track processes and of the detailed precipitation distribution where orographic effects are important (e.g. Pope and Stratton 2002).
High-resolution simulations of the climate system have generally only been run in uncoupled mode and often only at a regional scale where the simulation may be compromised by errors in the boundary forcing. The impact of details in the structures, for example the tightness of the Gulf Stream, on the evolution of the global coupled system have yet to be explored properly, although they may be substantial. For example, recent results from a European coupled model have shown a dramatic improvement in the mean tropical climate and the simulation of El Nino when the atmosphere is run at a resolution commensurate with that of the ocean (Guilyardi et al. 2003).
General Circulation Models still generally concentrate on the physical aspects of the climate system (e.g. radiation balance, clouds, convection, atmospheric and ocean heat transports). As shown in Figure 1, they most often treat the chemical and biological components of the Earth System as either fixed (e.g. vegetation) or time-varying boundary conditions (e.g. the concentrations of greenhouse gases). However, it is known that Ecosystems and Atmospheric Chemistry are intricately coupled to the physical climate system, because they are sensitive to climate and because they control the concentrations of greenhouse gases and aerosols (which themselves affect climate). For this reason the extension of physical GCMs to include biological and chemical components is seen as a major frontier in climate modelling.
Figure 1: The current state-of-the-art with regard to chemistry and ecosystem coupling in climate projections, with many of components calculated "offline".
Work has already begun on coupling ecosystems and atmospheric chemistry models to GCMs, and the Hadley Centre, with NCAS, is at the forefront of these efforts. For example, the Hadley Centre was the first to include the carbon cycle and dynamic vegetation as interactive elements in climate projections, with dramatic consequences (Cox et al., 2001), and has also been a pioneer in modelling interactions between climate and tropospheric chemistry (Johnson et al., 2001) and climate and stratospheric processes (Butchart et al., 2000). NCAS scientists have a long track record in fundamental chemistry/climate studies (e.g., Haigh and Pyle, 1979, 1982) and recently, for example, have pointed to important chemistry/climate processes related to the recovery of the stratospheric ozone layer (Hadjinicolaou et al., 2002) and the changing oxidizing capacity of the troposphere (Guang and Pyle, 2003). Each of these studies has demonstrated that the physical climate cannot be considered in isolation of wider Earth System interactions. The next stage will be to integrate these studies into an overall Earth system simulation, but this will be computationally very demanding and therefore impossible in the short-term without access to the extraordinary computing resources available at the Earth Simulator.
A key question for the chemical and ecosystem modelling is what resolution of the physical climate system is required for adequate simulation of the chemical processes. For example, many studies have demonstrated the potential importance of ocean eddy processes in the provision of nutrients to the ocean surface. Is it important to resolve such eddy fluxes in order to represent adequately the ocean’s biological carbon pump? Likewise, much atmospheric chemistry is likely to be sensitive to the mixing of air masses through synoptic or mesoscale processes.
Towards a next generation climate model:
We therefore propose to produce a unique Earth System Simulation of the 21st century, initially utilising the GCM and sub-models already available at the Hadley Centre, but also developing these further in collaboration with NCAS and our Japanese partners. In addition, higher resolution will also be implemented. This is seen as a clear imperative both not only for the chemical/biogeochemical systems but also for the physical system. Key features of the simulation are shown in Figure 2:
Figure 2: Modelling of climate, chemistry and ecosystems envisaged on the Earth Simulator.
The new model will include:
1. Unflux-corrected, high resolution, physical GCM, based on HadGEM1, and HiGEM which is being developed through the NCAS-led UK consortium.
2. Interactive carbon cycle utilising a higher resolution unflux-adjusted ocean for the first time.
3. Interactive stratosphere/troposphere chemistry using higher vertical resolution (50+ levels), in the first instance based on the STOCHEM model for the troposphere, but moving to the new integrated chemistry scheme being developed jointly by NCAS/ACMSU and the Met Office.
4. Ecosystem-chemistry interactions through land emissions of VOCs and ozone effects on plants, and oceanic emissions of DMS.
5. Effects of mineral dust on climate, both direct (through radiative forcing) and indirect (e.g. through fertilisation of ocean plankton growth)
6. Interactive lightning for NOx production and forest fire initiation.
The full simulation will be the most complete model representation of the Earth System ever achieved. However, to advance our scientific understanding and assess the modelling uncertainties due to individual processes, we plan to carry out a number of intermediate "control" simulations to isolate the various interactions, for example:
(a) HadGEM1/HiGEM ‘control’ to study interactions within the physical system
(b) Land carbon cycle and sulphur cycle feedbacks: (a) + interactive land carbon cycle + interactive sulphur cycle with indirect and direct effects (fixed DMS emissions and prescribed minor GHGs)
(c) Chemistry feedbacks: (b) + interactive tropospheric and stratospheric chemistry
(d) Ocean carbon cycle feedbacks: (c) + interactive ocean carbon cycle
(e) Iron fertilisation feedback by mineral dust
Each of these controls themselves will represent a unique milestone in Earth System modelling, but together they will allow us to answer key scientific and policy questions:
· How will the climate change in the 21st century and how will ecosystem-chemistry interactions affect this change?
· What are the critical feedbacks in the Earth System?
· What will be the wider changes in the life-support systems of the Earth (e.g. stratospheric ozone and UV, tropospheric ozone and human health, water availability)?
· Where are the dangerous thresholds in the Earth system?
The unison of the Hadley Centre, NERC and Japanese capabilities in Earth System Modelling, combined with the Earth Simulator facility, would allow these questions to be addressed more thoroughly than ever before, and the combination of increased resolution with a far more complete representation of important climate processes can truly be said to bring about a ‘next generation’ climate model.
Timescales and Wider Collaboration:
The proposed research and development programme represents a major advance in the modelling of the climate system, and would build on the HadGEM1 model, which is, itself, expected to represent a significant step forward from the current generation of climate models. To reach the proposed full Earth System model will entail a development programme of several years’ duration; however since so many aspects of the new model will, in themselves, be novel, a number of important scientific advances are expected to result along the way. Thus it is expected that the impact of the project (and of the Earth Simulator facility) on climate modelling science will become apparent at an early stage in the project.
Contacts:
Dr. David Griggs
Director of Climate Research
Hadley Centre for Climate Prediction and Research
Met Office
Prof. Julia Slingo
Director, NCAS Centre for Global Atmospheric Modelling
University of Reading
Dr Peter Cox
Head of Climate, Chemistry and Ecosystems
Hadley Centre for Climate Prediction and Research
Met Office
Prof. John Pyle
Director, NCAS Atmospheric Chemistry Modelling Support Unit
University of Cambridge
Dr Richard Wood
Manager, Ocean Model Validation and Techniques
Hadley Centre for Climate Prediction and Research
Met Office
References:
Butchart, N., J. Austin, J. R. Knight, A. A. Scaife, and M. L. Gallani, 2000. The response of the stratospheric climate to projected changes in the concentrations of well-mixed greenhouse gases from 1992 to 2051. J. Atmos. Sci., 13:2142-2159.
Cox, P. M., R. A. Betts, C. D. Jones, S. A. Spall, and I. J. Totterdell, 2000. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature, 408:184-187.
Guilyardi, E., S. Gualdi, J. M. Slingo and others, 2003: Does the atmosphere set the timescale for El Nino? Answers from am modular approach to coupled ocean-atmosphere. Submitted to Science.
Hadjinicolaou,P., A.Jrrar, J.A.Pyle and L.Bishop, 2002. The dynamically driven long-term trend in stratospheric ozone over northern middle latitudes. Quart. J. R Met. Soc, 128, 1393-1412.
Haigh, J. D. and J. A. Pyle , 1979. A two-dimensional calculation including atmospheric carbon dioxide and stratospheric ozone. Nature, 279, 222-224.
Haigh, J. D. and J. A. Pyle, 1982. Ozone perturbation experiments in a two-dimensional circulation model. Quart. J. R. Met. Soc., 101, 723-748.
Johnson, C. E., D. S. Stevenson, W. J. Collins, and R. G. Derwent, 2001. Role of climate feedback on methane and ozone studied with a coupled ocean-atmosphere-chemistry model. Geophys. Res. Lett., 28:1723-1726.
Pope, V. D. and R. A. Stratton, 2002: The processes governing horizontal resolution sensitivity in a climate model. Clim. Dyn., 19, 211-236.
Zeng, G and Pyle, J.A, 2003. Changes in tropospheric ozone between 2000 and 2100 modeled in a chemistry-climate model, Geophys. Res. Lett., 30(7), 1392, doi:10.1029/2002GL016708.