Thursday, December 31, 2009

Are Climate Computer models reliable?

A common objection of climate change "skeptics" is that the computer models are hopelessly primitive to represent the very complex climate system.

Ironically, sceptical scientists Lindzen and Spencer do use models to try to prove their point. But the models they use are primitive, simple types that exclude the many factors in the more modern models.  

Models are simply computerised theories, and are necessary because of the hugely complex nature of the atmospheric system. They are not perfect, but become more accurate as knowledge increases.

However, they have made successful predictions, which does give them credibility and validity.

In 1988 James Hansen correctly predicted that global temperature would climb until 2000.

Coby Beck also lists these correct predictions:

* the warming at the surface should be accompanied by cooling of the stratosphere and this has indeed been observed
* as well as surface temperatures warming, models have long predicted warming of the lower, mid and upper troposphere even while satellite readings seemed to disagree. But it turns out the satellite analysis was full of errors and on correction, this warming has been observed
* models expect warming of ocean surface waters as is now observed
* models predict an energy imbalance between incoming sunlight and outgoing infrared radiation. This has been detected
* models predict sharp and short lived cooling of a few tenths of a degree in the event of large volcanic eruptions and Mount Pinatubo confirmed this.
* models predict an amplification of warming trends in the Arctic region and this is happening

The models can also be tested by hindcasting : rolling the time back, entering the variables into the model, and seeing if the output matches the observations. They do.

The basic position of the skeptics is that they demand perfection. Since perfection is not attainable, they will accept nothing. By rejecting modelling, they reject climate science in its totality, which means that their position is incapable of refutation, and therefore not scientific.

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