Initial results

5000 runs have successfully completed and returned results to climateprediction.net!

Below are a few examples of what they did - the normal and the decidedly abnormal. This is very much raw, unprocessed data!

We will continue developing this page as we process the data coming back to us....

Thank you to everyone who is making this experiment possible!

click here to see:

A stable, 'normal' run

An unstable run

A warm, wet outlier

A cold, dry outlier

and here are some examples of things that can be seen using the new visualisation package which is being tested at the moment and should be available to everyone before the end of the year:

 

A cold, damp week in London, December 1828

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Most of the runs we are getting back at the moment look fairly similar to this 74958.

 

The left plot shows global mean temperature (the average temperature on the surface of the world), and the right plot the global mean precipitation (rain, snow etc.) for the same model run.

The blue part (1810-1825) is the 'spin-up' phase where the model was settling down - if this wasn't a straight line, the model run would probably have crashed. The green line (1825-1840) is the control part of the experiment, with pre-industrial carbon dioxide levels. We say that the model is 'stable' if this line is also approximately straight - nothing should be forcing the climate to change. The red line (2050-2065) is where the carbon dioxide levels have been doubled. The difference between this and the green line is what we're interested in. In this case, there is approximately a 3°C temperature increase, and a 5% increase in precipitation worldwide.

Why does the temperature rise when carbon dioxide is doubled? Click here to read more about the Greenhouse Effect.

Why does the precipitation rise when carbon dioxide is doubled? As the temperature of the air increases, for a fixed amount of water vapour in that air the relative humidity will decrease, so warm air can hold more water vapour before it saturates than cold air. However, this doesn’t determine how fast moisture circulates through the water cycle (you can read more about this here - follow the links to 'weather' and then 'water cycle'). The intensity of the water cycle is controlled at a global level by how fast water can condense rather than by how much water vapour there is in the atmosphere. As water vapour condenses to form clouds, it releases latent heat. If nothing removed this heat, the air would warm up and would be able to hold more moisture, so the condensation would stop. What actually happens is that the atmosphere gets rid of this heat, mostly in the form of longwave radiation. As the atmosphere warms up, outgoing longwave radiation increases (click here to read more about this) which allows more cloud droplets to form and so the whole water cycle intensifies.

Why does the precipitation fall initially when carbon dioxide is doubled? Initially, the carbon dioxide insulates the atmosphere, trapping longwave radiation. The amount of longwave radiation lost to space falls. Less cloud droplets can form because the atmosphere cannot get rid of the energy released by condensation fast enough.
Eventually, in most models, the temperature of the Earth increases and, as it does so, the outgoing longwave radiation increases again, compensating the direct insulating effect of increasing carbon dioxide. This makes future precipitation changes so much more uncertain than temperature changes: in some models, there might even be a net reduction in rainfall following a doubling of carbon dioxide for much more than a year or two.
You can read more about this in the Allen, Ingram and Stainforth Nature paper which is on our publications page.

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Several of the models are 'unstable', that is, the set of starting conditions and parameters supplied to the model meant that, even though it didn't do anything bizarre in the spin-up phase, it failed to settle at a given temperature in the control (green) phase. Experiments 40017 and 91121 are examples of this.

 

 91249 is an example of a stable experiment that went warmer and wetter than most in the doubled carbon dioxide phase.

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 40015 is an example of a stable experiment that went colder and drier in the doubled carbon dioxide phase.

This graph shows temperature (solid) and precipitation (dashed) over London, U.K. for 11-18th December, 1828 in one model. If you follow the temperature along from the start, you can see it rising during the day, then starting to fall ... but at 9pm that evening (you can't tell that from the graph) temperatures start to rise again... strange, until you see a huge spike in precipitation - so the rise in temperature was due to the warmer air behind a warm front. Another, wetter frontal system comes through a couple of days later, but the whole week the temperatures hover around freezing, so you can imagine it being grey and cold, and certainly very icy ....