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23 September 2014

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Thousands of you took part in the world’s largest climate experiment

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Distributed computing and climate change

This experiment was made possible by thousands you who downloaded a computer model that performed calculations to predict future climate. This technique is called distributed computing.

How does distributed computing work?
Modern home computers can perform billions of calculations a second. Most of the time, that's far more power than the average user needs – so even though you're working hard, your computer is just ticking over. Distributed computing projects make use of this spare computer potential.
Distributed computing is a particularly valuable tool for scientists who have large amounts of data to analyse, or who are modelling very complex systems like the Earth's climate.
Why is climate prediction so complicated?
Greenhouse gases affect how much of the Sun's energy the Earth loses back to space.
Diagram of atmospheric greenhouse reflectionGreenhouse gases affect how much of the Sun's energy the Earth loses back to space. Predicting global temperature change is hard, even though the principle sounds easy. In simple terms, energy reaches Earth from the Sun. Some of it is immediately reflected. Some is absorbed and then re-emitted. If the amount of energy that leaves the Earth is the same as the energy that arrives, then temperature stays the same. If not, then the Earth's temperature changes.
A huge number of factors affect how much energy the Earth reflects and absorbs. How much of the planet is covered in clouds – and what kind of clouds are they? How much ice is there at the poles? And of course, the amounts of so-called greenhouse gases like carbon dioxide play a role too.
All these factors make for an incredibly complex calculation. However, there's something else that makes climate prediction even harder: feedback mechanisms.
What are feedback mechanisms?
In relation to climate change, a feedback mechanism is something affected by climate change, which itself makes climate change happen more or less quickly.
Melting ice caps could accelerate global warming as less light is reflected back to space.
For example, heating the Earth could make the ice caps melt, which could mean that less of the Sun's light is reflected back into space, which could in turn cause the Earth's temperature to rise even faster.
Some feedback mechanisms could slow climate change – some could accelerate it. Either way, they make prediction harder and mean that scientists need to run many more models to get a feel for what is likely to happen.
Why so many people?
This experiment uses a computer model to try to calculate what the climate will be like in the future. However, small changes to the model can have large effects on the predictions that result.
There's only one way to get around this problem. The results of a single model cannot be gauged for accuracy. From many thousands of models, patterns emerge. Some results will be wildly inaccurate and predict warming or cooling outside what the Earth is likely to see. But if a significant percentage of results fall within a smaller range, the researchers can get a feel for how the climate might be changing.
Picture of Paul RosePaul Rose launched the BBC climate change experiment in early 2006.
There are other advantages too, as Nick Faull, one of the Oxford University scientists working on the experiment, explains. “Running so many models also helps us see which parameters are most important when trying to predict climate change. We can then put more effort into understanding the important parameters. Another reason this experiment is so exciting is that we are the only one that is running such a large quantity of runs with the ‘general circulation model’. These are the most complex models associated with climate modelling.”
Of course, it's not just about the state of the planet now. The biggest question of all is the effect that mankind is having on the climate. What happens if we continue to pump out greenhouse gases at the same rate as we are today? What happens if emissions grow? And by how much do we need to cut emissions to have an impact on global warming?
Why not use a supercomputer?
The aim was to better a supercomputer. Nick Faull explains: “The combined processing power of each person running a model is potentially greater than the most powerful supercomputer currently available to climate research. It’s also been fantastic to involve the public in climate research.”
What does each computer do?
In the BBC experiment, each computer ran one individual climate model. The model calculated the climate, year by year, from 1920 right through to 2080.
Calculating the climate for the 20th century might sound like an odd thing to do. It's a check of the validity of the model's parameters. If the model's prediction for 2007 is very inaccurate (for example, if the whole world turned to ice), then the model is rejected. But if not, the model continues into the 21st century.


See a map of everyone who took part in the experiment


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