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Last Updated: Wednesday, 19 April 2006, 18:44 GMT 19:44 UK
Error strikes 'BBC climate model'
Hands at a laptop keyboard.  Image: BBC
Climateprediction.net uses the power of thousands of ordinary PCs
A "major error" has been discovered in the world's biggest online climate prediction project, backed by the BBC.

The fault in a Climateprediction.net model launched in February causes temperatures in past climates to rise quicker than seen in real observations.

The program, which runs on users' computers when they are idle, aims to generate forecasts of climate change.

The project scientists have now fixed the fault and say the data collected so far is still useful.

"At some point in the future, we may have done an experiment like this anyway," Myles Allen, principal investigator of the project told the BBC News website. "People have not been wasting their time."

Global dimming

Climateprediction.net was established more than two years ago, but a new computer model was launched in February this year in collaboration with BBC Four TV.

The simulation is more sophisticated than previous versions and provides the scientists, they say, with a more accurate representation of the real world, including an ocean that interacts with the atmosphere.

The experiment uses "distributed computing", in which the combined power of numerous PCs is tapped rather than using a single supercomputer.

What we've seen in the runs is the unadulterated impact of global warming
Myles Allen, principal investigator, Climateprediction.net
Each participant downloads a program that runs unique climatic simulations from 1920 to 2080 to build a picture of the possible range of outcomes.

The error in the climate models has been traced to a file that is responsible for introducing man-made sulphate emissions into the atmosphere.

Sulphate particles reflect sunlight back into space causing a cooling of the atmosphere, in a phenomenon known as "global dimming".

"What we've seen in the runs is the unadulterated impact of global warming which means that all of the models have warmed up too fast," Dr Allen said.

Big disappointment

The problem was picked up by scientists when a handful of the 200,000 people that have downloaded the program reached the end of the simulation.

An announcement by Nick Faull, project coordinator of Climateprediction.net, was posted on the website's message board as soon as the scientists realised that the experiment would have to be started again.

"I regret to announce that we've recently discovered a major error in one of the files used by the climate model," it read.

Globe showing different temperature bands.  Image: BBC

"It's a big disappointment to have to give you this news."

Simulations of the 20th century were deliberately included in the model to allow its accuracy to be checked against real world observations.

A BBC statement said that the fact that the error had been identified showed that the checks were working.

"It's something that would have been very hard to anticipate," the corporation said.

"We're very grateful to everyone taking part and we hope they will continue to participate now that the experiment is back on track."

However, the scientists say that all is not lost for the data collected over the last two months.

"Running a model without global dimming is exactly the kind of thing we do in modelling centres," Dr Allen said.

These attribution studies, as they are known, allow scientists to determine what factors have contributed to climate change.

"We have done the most comprehensive attribution study by mistake."

The data will be used at a later date to determine the contribution of global dimming to temperature changes in the 20th Century.

Problem solved

However, some of the participants in the project have questioned why the model was not tested thoroughly before its release.

"I can't believe that this program wasn't completely tested before being released to thousands of people around the world," reads a post on the Climateprediciton.net message board

The team behind the model says the error was introduced by a minor last-minute change to the program, which made it easier to download.

It would have taken between three and four months to run the model for faults.

The error has now been fixed and all computers running the model will be automatically restarted at 1920.

The results of the experiment were due to be announced as part of the Climate Chaos season of programmes on BBC Four this summer.

The season will still go ahead but the programme containing the results will now be delayed until enough people have had time to rerun the model.


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