Wednesday, April 19, 2006


Error strikes BBC climate model .
Hands at a laptop keyboard.  Image: BBC 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 model launched in February causes temperatures in past climates to rise quicker than seen in observations.

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

The project scientists have now restarted the model but say the data collected so far is still useful.

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

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

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

The experiment uses "distributed computing" where the combined power of numerous PCs is tapped rather than using a single super computer.

What we've seen in the runs is the unadulterated impact of global warming
Myles Allan, principle investigator,

Each participant downloads a program which 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 Allan 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.

Globe showing different temperature bands.  Image: BBC

An announcement by Nick Faull, project coordinator of 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.

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

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 Allan 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 twentieth 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 message board

The team behind the model say the error was introduced by a minor last-minute change to the programme, 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 BBC experiment were due to be announced as part of the Climate Chaos season of programmes on BBC Four this summer.

The results and the programme will now be delayed until enough people have had time to rerun the model.



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