There were 39 presentations in 4.5 days, some describing the Grid's enabling potential for international collaboration within the community of climate system modelling (CCSM). The talks were crammed with technical information on how to use parallel supercomputers for computation using mathematical models, which describe climate/weather patterns over time. They were interspersed with weather maps and video pictures from simulations and these were compared with satellite pictures of the behaviour of actual weather events.

Why are meteorologists doing all this Earth System Modelling and what is the urgency? Dramatic reports of flooding and other climate change events now appear frequently in the press and on television. Climate simulations show that intensely hot summers and increase in rainfall, causing flooding, are likely to become more common. These images are injecting a political dimension into the proceedings.

The destruction of New Orleans by hurricane Katrina provides a cautionary tail. The Earth System Models correctly predicted the path of Katrina days before it hit New Orleans, communicated their predictions to the authorities, yet the emergency response infrastructure failed in its mission to minimise damage to property, affect prompt evacuation of citizens, to minimise loss of life and inevitable pain. It is easy to scapegoat individuals about this failure, but I think it goes much deeper than that. It is a systemic failure on how fast scientific discovery is inserted into public domain infrastructures for the benefit of society at large. Reporting new knowledge in scientific forums is not enough. It requires effort to engage the political class so it can take ownership of this knowledge, inform policy for risk management infrastructure, so it becomes part of the fabric of the emergency response process. In the case of Katrina, the fact that the Bush administration is in denial about global warming exacerbated this lack of preparation. This denial mindset inevitably downgrades fiscal requirements to deal with potential risk. For the people of New Orleans, it was a catastrophic tragic outcome.

The Intergovernmental Panel for Climate Change (IPCC) experiments have been completed this summer and the fourth assessment report, to be published in 2007, is being prepared. The scientific results from these experiments predict a grim future. The trend is clear. More extreme weather, flooding, droughts, stronger and more frequent hurricanes and climate changes involving desertification and higher sea levels, are inevitable during this century. The experiments show that human activity is contributing to global warming. The reduction of snow in the north, the melting of glaciers, the projection of no snow in the north in year 2100 (even at the North Pole) and the implied rise in sea level, raise questions on the state of the atmosphere, the ocean, sea-ice, the land surfaces and humankind. In short, there is a perceived pending catastrophe, because of global warming exacerbated by greenhouse gases and other pollutants from human activities.

Some scenarios show that sea level rise alone could deprive a billion people of food in the next hundred years. Insurance companies cannot protect against consequences of this magnitude. Thus the stakes are high and finding answers to the socio-economic effects of climate change has climbed to the top of the political agenda, but sadly not in the USA where over a quarter of pollutants and greenhouse gases are generated, as the communicate from the recent G8 meeting at Gleneagles in August, shows.

The key goal of the climate change efforts is to develop and enhance our capability to monitor and predict how the Earth System is evolving. Temporal scales seasonal and inter-annual, weather forecasting and climate change predictions are dominated by initial conditions of the atmosphere, the oceans and by forcing factors (naturally-occurring and human-induced).

Dr. Warren Washington, Chairman of the NSF National Science Board, presented the findings of his team at NCAR, on: "IPCC climate change simulations of 20th and 21st century: Present and Future". He stated that: "The Community Climate System Model (CCSM), has produced one of the largest data sets for the IPCC fourth assessment. As a result of this and other assessments, most of the climate research science community now believes that humankind is changing the earth's system and that global warming is taking place".

CCSM is a comprehensive system for simulating the past, present and future climates of the Earth. It grew out of a collaborative development effort involving NCAR, university investigators and scientists from several USA federal agencies. One of the distinguishing features of CCSM is that the complete source code, documentation and simulation data sets are freely distributed to the international climate research community. It initially consisted of four major components representing the atmosphere, ocean, sea ice, and land surface. The exchange of energy, water and other constituents at the interfaces among these components is simulated using a flux coupler.

The current version of the model, CCSM3, has been developed to facilitate work on a wide variety of scientific problems. These include the interactions between aerosols and climate, the relative importance of natural and anthropogenic forcing from the last millennium, and the nature of abrupt climate change. Results from CCSM3 form the basis for NCAR's contribution to forthcoming international (IPCC and WMO) climate fourth assessments. This talk chronicled the major new features and improvements in CCSM3 relative to its predecessors.

These include new radiation and cloud parameterisations in the atmosphere; heating of the ocean surface by chlorophyll and detailed vegetation ecology. The improvements in simulations of present-day climate produced by the new model physics were illustrated with recent coupled experiments. Global and regional climate aspects investigated using a climate model included El Nino, La Nina, monsoons, the north Atlantic oscillation and the Arctic oscillation.

The controversy of global warming was settled in year 2005. With more green house gases climate models project: Troposphere temperature increase, stratosphere temperature decrease, surface temperature increase and troposphere warms more than earth surface. Observations show that since 1960, surface and troposphere warm about the same rate. There are strong decreases in stratosphere temperature and increases in tropopause height since 1979 (T. Karl of NOAA).

Climate change scenarios show that: "At any point in time, we are committed to additional warming and sea level rise from the radiative forcing already in the system. Warming stabilizes after several decades, but sea level from thermal expansion continues to rise for centuries. Each emission scenario has a warming impact".

Climate models can be used to provide information on changes in extreme events such as heat waves. Heat wave severity is defined as the mean annual 3-day warmest night-time minima event. The Model compares favourably with present-day heat wave severity. In a future, warmer climate, heat waves become more severe in southern and western North America, and in the western European and Mediterranean regions.

In the next few years, the CCSM will be further expanded to include reactive troposphere chemistry, detailed aerosol physics and microphysics, comprehensive biogeochemistry, and ecosystem dynamics, and the effects of urbanization and land use change. These new capabilities will considerably expand the scope of earth system science that can be studied with CCSM and other climate models of similar complexity. Higher resolution is especially important near mountains, river flow, and coastlines. Full hydrological coupling including ice sheet is important for sea level changes. It will include better vegetation and land surface treatments with ecological interactions as well as carbon and other biogeochemical cycles.

For example, one of the carbon cycle methods being tested is based on microbe activity. There is a strong feedback between decomposition and plant growth: soil mineral nitrogen is the primary source of nitrogen for plant growth. Nitrogen fixing bacteria/algae are very important, however, there are limited field and laboratory data, on their role. It has been suggested that their role in nitrogen fixing can result in a shift from 'carbon source' to 'carbon sink', under a warming scenario.

The proposed DoE climate science Computational End Station (CES), set up at ORNL, will address Grand Challenge scale problems, to predict future climate change resulting from various energy options. It will use the CCSM for studies of model biases, climate variability, abrupt climate change, and global carbon and other chemical cycles and pursue high resolution, atmosphere and ocean studies.

The computer requirements, for the next generation of comprehensive climate models, can only be satisfied by major advances in computer hardware, software, and storage. The classic climate model problems with supercomputer systems are: The computers (with the exception of vector systems) are not balanced between processor speed, memory bandwidth and communication bandwidth between processors, including global computational needs. They are more difficult to program and optimize, it is hard to get I/O out of computers efficiently and computer facilities need to expand archival data capability into the petabyte range. There is a weak relationship between peak performance and performance on actual working climate model programmes.

The major atmospheric research centres now have systems consisting of several thousands of IBM P3/4/5 processors, up to a thousand Cray X1E vector processors, or several hundred NEC SX-6 and SX-8 vector processors. In either case they can achieve about a half Teraflop/s sustained and sometimes Teraflop/s on certain application codes. The exemption to this is the Earth Simulator in Japan, based on NEC SX-6 technologies (5120 processors), which delivers over 12Teraflop/s sustained performance.

Thus with sustained performance Teraflop/s computing on the horizon and occasionally on stream, meteorologists are moving from Climate to Earth System Modelling (ESM). This is because feedback loops of climate system with other relevant systems like ecology and socio-economy are not negligible. Climate Modelling is not possible without proper representation of these systems hence ESM. Earth System Modelling is: Multi (time and space) scale, multi process, multi topical (physics, chemistry, biology, geology, economy…). It is both very compute and data intensive. Some people claim it requires several orders of magnitude more computing power to tackle the problem. Petaflop/s and Hexaflop/s are therefore eagerly awaited.

Tom Bettge, Deputy Director, scientific computing division at NCAR said: "A factor of 25 times the present NCAR computing resources is needed to accommodate CCSM requirements over the next 2 years, to prepare for the Next IPCC assessment starting in year 2007. How this deficiency is to be remedied is a great challenge. Although special architectures, like the IBM Blue Gene R&D system, for protein folding, is delivering good results in its niche area, this architecture is not suited to ESM, which needs a small number of fat nodes, rather than the thousands of processors as in the Blue Gene”.

It was noted that despite many computing centres having IBM systems with 15 to 25Teraflop/s peak performance, these centres are only delivering a few hundreds of Gigaflop/s sustain performance to the user application. Presently CCSM is in the hundreds of Gigaflop/s era. Only Earth Systems Models running on the Japanese Earth Simulator (ES) have graduated to the Teraflop/s era. This was aptly illustrated by the talk from Michel Desgagne, Environment Canada, on the study of Hurricane behaviour. His simulations were performed on the ES and achieved 13Tflop/s of sustained performance, using 495 compute nodes, and 7TeraBytes memory. Each run took 7 to 8 days wall clock time.

Desgagne said: "Recent studies have shown that very high resolution is essential to properly resolve waves that have direct impact on the intensification of hurricanes. In particular, innovative potential vorticity diagnostic tools were applied to diagnose inner spiral bands formed in explicitly simulated hurricanes. It was shown that wave-number one and two anomalies are in fact vortex Rossby waves that explain 40% to 50% of the wave activity in a period of 24 hours. These meso-vortices within the inner core of a hurricane are responsible for the dynamical processes controlling the redistribution of angular momentum and numerical resolution of these vortices could help to more accurately predict the intensification of hurricanes".

For the Vortex Rossby waves (VRWs), it was found that a 6Km resolution was not good enough, a 1Km resolution had to be used to get useful results. What has recently being identified is a Rossby wave train starting from the Indonesia area moving across the oceans causing bad weather. Using the ES, one achieves 1 hour simulation for 1 hour of computation. To follow and analyse VRWs across the globe, one needs to attain a day's simulation for 10 minutes computation. This translates to approximately 150 times more computing than that achieved on the ES, i.e. ~2Petaflop/s sustained performance.

Several talks concentrated on projects implementing Earth System Modelling Frameworks, ESMF in the USA and PRISM in Europe. PRISM has now moved from an R&D project to the status of PRISM Support Initiative (PSI) delivering a service. For example, PRISM will be the modelling environment at DKRZ for the IPCC fifth assessment.

During the last workshop in 2003 a strong emphasis was placed on data management and the challenges this entails. This time the emphasis was more on power used by supercomputers and the footprint, facility space requirements, which are of most concern.