Bearing this in mind, I think most people--including me--missed the biggest part of the climate emails story. Sexing up a graph is at best a misdemeanor. But a Declan McCullough story suggests a more disturbing possibility: the CRU's main computer model may be, to put it bluntly, complete rubbish.

As the leaked messages, and especially the HARRY_READ_ME.txt file, found their way around technical circles, two things happened: first, programmers unaffiliated with East Anglia started taking a close look at the quality of the CRU's code, and second, they began to feel sympathetic for anyone who had to spend three years (including working weekends) trying to make sense of code that appeared to be undocumented and buggy, while representing the core of CRU's climate model.



One programmer highlighted the error of relying on computer code that, if it generates an error message, continues as if nothing untoward ever occurred. Another debugged the code by pointing out why the output of a calculation that should always generate a positive number was incorrectly generating a negative one. A third concluded: "I feel for this guy. He's obviously spent years trying to get data from undocumented and completely messy sources."



Programmer-written comments inserted into CRU's Fortran code have drawn fire as well. The file briffa_sep98_d.pro says: "Apply a VERY ARTIFICAL correction for decline!!" and "APPLY ARTIFICIAL CORRECTION." Another, quantify_tsdcal.pro, says: "Low pass filtering at century and longer time scales never gets rid of the trend - so eventually I start to scale down the 120-yr low pass time series to mimic the effect of removing/adding longer time scales!"



The emails seem to describe a model which frequently breaks, and being constantly "tweaked" with manual interventions of dubious quality in order to make them fit the historical data. These stories suggest that the model, and the past manual interventions, are so poorly documented that CRU cannot now replicate its own past findings.

That is a big problem. The IPCC report, which is the most widely relied upon in policy circles, uses this model to estimate the costs of global warming. If those costs are unreliable, then any cost-benefit analysis is totally worthless.

Obviously, this also casts their reluctance to conform with FOI requests in a slightly different light.

That's not reason to abandon efforts to control our carbon emissions--as I say, they're still very likely to be problematic. But if the model turns out to be as bad as initial reports seem to imply, we should probably hold off on policy recommendations until we have a slightly better handle on the likely outcomes.