Wednesday, September 25, 2013

Climate modelling - on your own PC

There is a lot of uncertainty in the community about man made global warming. There is no doubt that CO2 levels are around 150% of long term historic levels. There are indications that the climate is warming and that the CO2 level is the likely cause but weather is highly variable and observed warming is still of the same order as natural variations in weather.

The strongest argument for anthropogenic climate change is the work of climate scientists who model the increased radiative forcing of CO2 along with many positive and negative feedback loops on their supercomputers. We believe, if we trust them, that the predicted warming is around 1C, the same as is being experienced.

We, till now, have been unable to verify the models they use. It is an issue of trust, trusted sources, climate skeptics simply trust different sources.

Compare with flat earth, hygiene, vaccination and other beliefs that have been controversial at times. All can be experimentally tested. Its fairly easy to understand how they can be tested. If we could be bothered, we could test them at home. We know that they have been tested time and time over.

With advances in computers, home computers are now as fast as the supercomputers of 1988, if we want we can run a 1988 climate simulation on our PC. 100 years takes overnight to run. :

"EdGCM, or the Educational Global Climate Model, is a suite of software that allows users to run a fully functional 3D global climate model (GCM) on laptops or desktop computers. {read a general description of the software}
At its core, EdGCM uses a Global Climate Model (GCM) developed at NASA’s Goddard Institute for Space Studies, which has been used by researchers to study climates of the past, present and future."

EdGCM is free for 30 days then $199.

EdGCM has a fancy graphical front end but it uses  you can download, inspect or compile the Fortran source code if you are a relatively skilled hacker.

"Model II first described and published by Hansen et al., 1983. This model was developed at the NASA Goddard Institute for Space Studies beginning in the late 1970's and was the primary GCM maintained and used by GISS scientists until the early 1990's. Model II parameterizations and control runs are described in Hansen et al., 1983 and the original NASA/GISS global warming simulations were performed using this model and published in Hansen et al. 1988"

How good was Model II ? If your standard was its ability to predict weather, or the average temperature of a particular year, it was not good, but not so bad when looking at average warming rates.

temp trends.png

Here is another model, simpler and faster to run. It does not model day/night and the atmosphere is a single layer. 

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