Friday, September 20, 2013

Temperature trickery

During the late seventies and early eighties our lab looked after a small weather station on behalf of the Met Office. We logged rainfall, snow, temperature, sunshine hours and every now and then a chap from the Met Office would collect the data.

All data was hand written of course and ever since climate change came to be such a hot topic I’ve often wondered how reliable it was. In my view those far off days have something to tell us about historical data and the fact that it was collected and transcribed by people, not automated instruments. Historical protocols and historical behaviour – a minefield of unknowns.

To record daily maximum and minimum temperatures, we used a simple max/min thermometer housed in a wooden Stevenson screen. Every day someone from the lab would read the two temperatures, write them down and reset the thermometer.

If we missed a day, which happened occasionally for a variety of reasons, then the Met Office chap would nag us about it when he collected the data, look up a temperature record of the nearest station to ours and insert the readings into our record. He once told me that this was standard procedure – they didn’t accept incomplete data.

Yet at the time the data was fit for purpose, although that doesn’t mean it was fit for a far more tightly specified purpose dreamed up decades later.

In those days nobody knew that such temperature records would one day be used to justify global political decisions on energy policy. Nobody knew that long term temperature changes of less than one degree centigrade would acquire such dramatic significance.

Not that our station was ever likely to figure in these games I hasten to add. It closed some time ago. I’m merely dredging up some memories to highlight the tricky nature of historical temperature data. Stripping off some of the gloss you might say. There is a lot of that in climate science.

For example, our thermometer was never recalibrated. I’m sure it was checked before being installed, but even simple thermometers change over time and today it would be regularly calibrated against a certified standard. Ours wasn’t - ever.

Apart from the unknown condition of the thermometer, how many errors were made by people who took the readings and wrote them onto sheets of paper come wind, rain or snow?

In my experience, scientists are reluctant to take cognisance of human error even for highly uncertain factors such as historical and somewhat loosely defined protocols. Yet the historical global temperature record and our evidence of recent warming relies on such data.

Were the protocols and equipment used my lab capable of detecting a small temperature rise over a century?
One degree? No.
Two degrees? Doubtful.
Three degrees? Maybe.

Of course this is merely my opinion. I don’t actually know and neither does anyone else. Nobody can go back and calibrate our thermometer, review the protocol we followed and audit the way we followed it. There are some things we could do such as comparing our record to the record of nearby thermometers, but is that sufficient to detect small long term changes?

Taking the wider view, are we able to estimate such changes from long historical records based on protocols not designed for that purpose? Always assuming written protocols were used of course - and what about calibration facilities? How many were calibrated against the equivalent of NPL standards? Some? A few? None?

Yet in terms of time span, manual surface temperature records derived from a range of old and possibly dubious measurement protocols account for at least two thirds of our surface temperature record for the past century.

Note this post gives an excellent insight into the pitfalls of temperature measurement.

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Sackerson said...

That's worrying - and humbling for big-picture climate scientists. A really pregnant piece.

Mark In Mayenne said...

Scientists are predicting about a 5 degree increase in global mean temperature over the next 200 to 500 years. That's at most 0.025 degrees per year, on average.

During a year where I live, the temperature ranges from -15 degrees to +30. Scientists are not predicting warming by looking for 0.025 degree changes amongst all that noise.

Inaccuracies in direct temperature measurement have nothing to do with anything.

Sackerson said...

Mark - except that if the effects over a few years are so small and measurements are so unreliable, there's some question about the reality of the effects.

Not that I don't think the precautionary principle isn't important.

Though we might be able to do something to mitigate global warming, what would we do if the evidence suggested global cooling?

A K Haart said...

Sackers and Mark - I tend to see this problem as yet another reason to be sceptical and even cynical about policy-led conclusions.

At the moment, the climate itself is beginning to direct this debate, not science or climate models.

Woodsy42 said...

I don't know what you are worried about. Your measurements - inaccurate though they may be - are orders of magnitude more reliable than the figures 'deduced' from tree rings which are used at the other end of the comparison.

A K Haart said...

Woodsy - deduced only from certain selected trees too.