Tuesday, March 17, 2009

Average of Averages - A Great Basis for Public Policy?

What is an average global temperature?

This may sound like an odd question, but it is worth a moment. Each location in the world has a temperature. This temperature depends on a range of variables, which are quite complex. They include wind patterns, proximity to oceans, mountains and rivers, population and building density and so on. In fact, we all know that there are such things as regional and very local micro-climates – Napa Valley, Okanagan Valley in Canada are all microclimates, ideal for wine growing. Some regions are historically hotter than others – proximity to the earth’s central regions and others are colder than others – the Arctic and Antarctic, for example. At any one moment in time, the temperature at all of these locations is different. We average them and get a global temperature average. We take averages over a period of time at each location (like a year) and then average all of these – an average of averages.

A parallel that occurs to me is to average everyone’s cell phone number to get a global average cell phone number. While this would be totally meaningless – you could use the number for reporting, but what does it really represent? - you can’t actually call anyone with it and it tells us nothing – but it is the same basic idea.

What matters when we take the measures is where the data comes from. A lot of the earthbound temperature monitoring stations are in locations where there are people – Universities, car parks, meteorological stations and so on. Many of the stations in China, Indonesia, Brazil and elsewhere are in urban areas (such as Shanghai or Beijing). In some of the major indexes (e.g. CRU,NOAA), there appears to be varying attempts to adjust for urbanization. GISS does report an effort to adjust for urbanization in some cases, but their ability to do so depends on the existence of nearby rural stations, which are not always available. Thus, there is a real concern that the need for urban adjustment is most severe in the very areas where adjustments are either not made or not accurately made. Then we are not comparing like with like over time.

Once we have an average global mean temperature, what can we do with it? As far as I can tell, nothing. It means very little. Yet, it is being used as a basis for some of the campaigning and polemics of climate change alarmists. They are concerned that the average may go up by 2-4 degree C by 2100. This would imply, they claim, massive warming of the earth. But lets look at this for a moment.

Today it is -15C here in Edmonton and +12 in London, UK. When add these up we get an average of -1.5. If the temperature in London remains roughly +12 but that in Alberta moves to -5 the average is now +3.5 which looks like a massive warming, but we’re still bloody cold and nothing has changed in London.

Two physicists have recently looked in depth at this issue and conclude, as I have done, that the only climate that matters is regional/local and that we should be seeking to understand global climate as a chaotic collection of local climates. They also see global mean temperatures as a fiction.


Joe Bower said...

Now take you average of averages and help explain to teachers and parents why classroom averages are statistically unsound, in a similar manner that you do with climate change. Now that would be cool.

Stephen Murgatroyd said...

I agree - Pasi Sahlberg makes the point that in Alberta differences within schools are greater than differences between them...this is something we can do something about.