Climateprediction.net
From Freepedia
Climateprediction.net, or CPDN, is a distributed computing project to investigate and reduce uncertainties in climate modelling. It aims to do this by running hundreds of thousands of different models (a large ensemble) using the donated idle time of ordinary personal computers, thereby leading to a better understanding of how models are affected by small changes in the many parameters known to influence the global climate. Anyone with a reasonable computer can join and help this project by running their own model.
It is run primarily by Oxford University in England and has the most computing power and generated more data than any other climate modelling program.
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The model
The experiment is run with HadSM3, which is the atmosphere from the HadCM3 model but with only a "slab" ocean rather than a full dynamic ocean. This is faster (and requires less memory) than the full model, but lacks dynamical feedbacks from the ocean, which are incorporated into the full coupled-ocean-atmosphere models used to make projections of climate change out to 2100.
Each downloaded model comes with a slight variation in the various model parameters.
There is an initial "calibration phase" of 15 model years in which the model calculates the "flux correction"; extra ocean-atmosphere fluxes that are needed to keep the model ocean in balance (the model ocean does not include currents; these fluxes to some extent replace the heat that would be transported by the missing currents).
Then there is a "control phase" of 15 years in which the ocean temperatures are allowed to vary. The flux correction ought to keep the model stable, but feedbacks developed in some of the runs. There is a quality control check, based on the annual mean temperatures, and models which fail this check are discarded.
Then there is a "double CO2 phase" in which the CO2 content is instantaneously doubled and the model run for a further 15 years, which in some cases is not quite sufficient model time to settle down to a new (warmer) equilibrium. In this phase some models which produced physically unrealistic results were again discarded.
The quality control checks in the control and 2*CO2 phases were quite weak: they suffice to exclude obviously unphysical models but do not include (for example) a test of the simulation of the seasonal cycle; hence some of the models passed may still be unrealistic. Further quality control measures are being developed.
The temperature in the doubled CO2 phase is exponentially extrapolated to work out the equilibrium temperature. Difference in temperature between this and the control phase then gives a measure of the climate sensitivity of that particular version of the model.
History
Myles Allen first thought about the need for large ensembles in 1997 but was only introduced to the success of SETI@home in 1999. The first funding proposal in April 1999 was rejected as utterly unrealistic.
Following a presentation at the World Climate Conference in Hamburg in September 1999 and a commentary in Nature entitled Do it yourself climate prediction in October 1999, thousands signed up to this supposedly imminently available program. The Dot Com bust did not help and the project realised they would have to do most of the programming themselves rather than outsourcing.
It was launched September 12, 2003 and on September 13, 2003 the project exceeded the capacity of the Earth Simulator to become the world's largest climate modelling facility.
The 2003 launch only offered a Windows "classic" client. On 26th August 2004 a BOINC client was launched which supported Windows, Linux and Mac OS X clients. Both will continue to be available for a number of years.
A ThermoHaline Circulation slowdown experiment was launched in May 2004 under the classic framework to co-incide with the film The Day After Tomorrow. This program can still be run but the scientific analysis has been completed (still being written up into a thesis) with no further planned research.
Future plans include releasing a sulfur cycle model and a high resolution model as well as an atmospheric-ocean coupled model to carry out a hindcast from 1950 to 2000 and a forecast of 2000 to 2050. This will be done under the BOINC framework.
Results to date
The first results of the experiment were published in Nature in January 2005 and show climate sensitivities ranging from less than 2 °C to more than 11 °C (see abstract or full version).
Explanation
Climate sensitivity is defined as the equilibrium response of global mean temperature to doubling levels of carbon dioxide. Current levels of carbon dioxide are around 380 ppm and growing at a rate of 1.8 ppm per year compared with preindustrial levels of 280 ppm. Therefore doubling is an extreme change that does not happen rapidly. The experiment is carrying out this forcing more as a way of finding out about what the model does than about saying the outcomes are realistic.
Climate sensitivities of greater than 5 °C are widely accepted as being catastrophic but are considered unlikely. The possibility of such high sensitivities being plausible given observations had been reported prior to the Climateprediction.net experiment but "this is the first time GCMs have produced such behaviour".
Even the models with very high climate sensititivity were found to be "as realistic as other state-of-the-art climate models". The test of realism was done with a root mean square error test. This does not check on realism of seasonal changes and it is possible that more diagnostic measures may place stronger constraints on what is realistic. Better tests of realism are being worked on.
It is important to the experiment and the goal of obtaining a probability distribution function (pdf) of climate outcomes to get a very wide range of behavours even if only to rule out such behaviour as not realistic. Unless you start with the whole range of behaviours, you would not be able to have confidence that a pdf was reliable. Therefore it is good to see that models with climate sensitivity as high as 11 °C are included. More worrying is the lack of models with climate sensitivity of less than 2 °C. The sulfur cycle experiment is likely to extend the range downwards.
Use in education
There is an Open University short course and teaching material available for schools to teach subjects relating to climate and climate modelling.
Off-shoot Experiments
Climateprediction.net is also performing and planning a number of off-shoot experiments.
- THC - an investigation of how the climate might change in the event of a decrease in the strength of the ThermoHaline Circulation. This experiment has now been closed to new participants as they have sufficient results.
- Sulfur Cycle - an investigation of the effect of sulphate aerosols on the climate. The experiment will model sulfur in a number of compound forms including Dimethylsulfide and sulphate aerosols. This experiment will only be run under BOINC, and is projected to start in the second half of 2005.
- Coupled Model - inclusion of oceanic influences into the basic model. This is a pre-requirement for experiment 2 of the main experiment. This will also be BOINC only and should start in 2006.
- High Resolution Model - this will be a slab model as normal followed by a period calculating at high resolution.
Visualisations
Most distributed computing projects do have screensavers to visually indicate what they are doing but this falls short of giving the impression that the participant is shown the result. In contrast, Climateprediction.net not only uses a built-in visualisation to show the climate of the world being modelled but it is interactive to show different aspects of climate and result graphs are available on the website. In addition, there are other advanced visualisation programs that allow the user to see more of what the model is doing, as well as compare it to what it did previously and other models. Many more graphs and maps can be created.
The Climateprediction.net "Advanced Visualisation" progams in use are CPView and the IDL Advanced Visualisation. They will both do quite a lot of the same things. CPView was written by a participant, Martin Sykes. The Advanced Visualisation was written by Andy Heaps of the University of Reading (UK), and modified to work with the BOINC version by Tesella Support Services plc.
Only CPView allows you to look at unusual diagnostics (rather than the usual Temperature, Pressure, Rainfall, Snow, and Clouds). See Data Index. Up to 5 sets of data can be displayed on a map. It also has a wider range of functions like Max, Min, further memory functions, and other features.
The Advanced Visualisation has functions for graphs of local areas and over 1 day 2 days and 7 days (as well as the more usual graphs of season and annual averages which both packages do). There are also Latitude - Height plots and Time - Height plots.
The download size is much smaller for CPView and CPView works with Windows 98.
See also
- List of distributed computing projects
- Climate model
- Global climate model
- Distributed computing
- BOINC
- Climate ensemble
